What to Expect Week-by-Week

Want to know what to expect during your pregnancy? Whether you're planning to get pregnant or you already are, you've come to the right place! Each week of pregnancy includes a description of your baby's development, as well as an explanation of the changes taking place in your body. You'll also find important medical info that will help keep you and your baby healthy.

A Word About Due Dates and Trimesters

After you announce your pregnancy, the first question you'll probably be asked is "When are you due?" At your first prenatal visit, your health care provider will help you determine an expected delivery date (EDD). Your EDD is 40 weeks from the first day of your last menstrual period (LMP).

It's important to remember that your due date is only an estimate — most babies are born between 38 and 42 weeks from the first day of their mom's LMP and only a small percentage of women actually deliver on their due date.

Another common term you'll hear throughout your pregnancy is trimester. A pregnancy is divided into trimesters:

the first trimester is from week 1 to the end of week 12
the second trimester is from week 13 to the end of week 26
the third trimester is from week 27 to the end of the pregnancy

Getting Started

To get started, simply view the week of pregnancy you'd like to know more about. Check back every week, or as often as you like, during your pregnancy to see how your baby is developing and to find out what changes you can expect in your own body, too!

First trimester

Week 1

Your baby's development

This first week is actually your menstrual period. Because your expected delivery date (EDD) is calculated from the first day of your last period, this week counts as part of your 40-week pregnancy even though your baby hasn't been conceived yet.

Your body

During pregnancy, your healthy habits and your baby's health go hand in hand. While planning to conceive, take the time to prepare your body for motherhood. Before becoming pregnant, you should:

Avoid alcohol, drugs, and tobacco products. These substances can cause birth defects, fetal alcohol syndrome, respiratory problems, low birth weight, and other health problems.
Talk to your doctor about any prescription and nonprescription (OTC) drugs you are taking. You'll need to take special precautions with medications because many prescription and over-the-counter medications can negatively affect the fetus. But don't stop taking prescription drugs without consulting your health care provider, who will help you weigh the potential benefits and risks of stopping your medications.
Maintain a diet that contains an adequate amount of vitamins, especially folic acid. Women who are attempting to become pregnant should take 400 micrograms of folic acid a day. Adequate folic acid intake reduces the risk of neural tube defects (birth defects caused by incomplete development of the brain or spinal cord), such as spina bifida. Be sure to talk to your health care provider about taking a folic acid supplement while you are trying to conceive.

Week 2

Your baby's development

This may sound strange, but you're still not pregnant! Fertilization of your egg by the sperm will only take place near the end of this week — read more about fertilization in the Your Body section below.

Although you'll have to wait to find out what color to paint the nursery, your baby's gender will be determined at the moment of fertilization. Out of the 46 chromosomes that make up a baby's genetic material, only two — one from the sperm and one from the egg — determine the baby's sex. These are known as the sex chromosomes. Every egg has an X sex chromosome; a sperm can have either an X or a Y sex chromosome. If the sperm that fertilizes your egg has an X chromosome, you'll have a girl; if it has a Y chromosome, your baby will be a boy.

Your Body

Your uterine lining, which will nourish the baby, is developing, and your body secretes follicle-stimulating hormone (FSH), which stimulates an egg to mature. At the end of this week, you will be at the midpoint of your menstrual cycle (if you have a regular 28-day cycle), and ovulation will occur (your ovary will release an egg into the fallopian tube).

This is when you're most likely to conceive. If you have sexual intercourse without protection around the time that you ovulate, you can become pregnant. After your partner ejaculates, millions of sperm travel through the vagina, and hundreds make it to the fallopian tube, where your egg is waiting. One sperm generally succeeds in penetrating the egg, and fertilization takes place. When that happens, you will be pregnant — although you will not be feeling any body changes just yet.

Week 3

Your baby's development

Even though you may not feel that you're pregnant yet, you have a baby growing and developing inside of you!

Your baby was just conceived, but already is working overtime. The fertilized egg goes through a process of cell division. About 30 hours after fertilization, it divides into two cells, then four cells, then eight, and continues to divide as it moves from the fallopian tube to the uterus. By the time it gets to the uterus, this group of cells looks like a tiny ball and is called a morula.

The morula becomes hollow and fills with fluid — it is then known as a blastocyst. Near the end of this week, the blastocyst will attach itself to the endometrium, the lining of the uterus. This is called implantation. The implantation in the uterus creates an essential connection — the endometrium provides the developing embryo with nutrients and removes wastes. Over time, this implantation site will develop into the placenta.

Your Body

Getting enough of certain nutrients, such as folic acid, protein, calcium, and iron, is essential for your baby's development. A folic acid supplement is particularly important because folic acid helps prevent defects of the neural tube (the structure that gives rise to the brain and spinal cord), which forms very early in pregnancy.

Your intake of protein, which is used to create new tissue, should increase during pregnancy. Calcium aids the development of bones and teeth, so make sure you're getting a good dose of dairy products, leafy green vegetables, and legumes (beans, peas, lentils, etc.). Iron is essential during pregnancy as you support your baby's increasing blood volume. Good sources of iron include red meat, legumes, eggs, and leafy green vegetables.

Week 4

Your baby's development

Four weeks into your pregnancy, your baby (now an embryo) consists of two layers of cells — the epiblast and the hypoblast. These eventually develop into all of your baby's organs and body parts.

Two other structures that develop now are the amnion and the yolk sac. The amnion, filled with amniotic fluid, will surround and protect the growing embryo. The yolk sac will produce blood and help to nourish the embryo until the placenta takes over that role.

Your Body

The embryo continues to implant in your uterus, burying itself deep within the endometrium. Some women have slight cramping and spotting during this week while implantation happens. They might mistake this for a period, especially because this is around the time their monthly period was due.

Once implanted, the embryo starts to make a hormone called human chorionic gonadotropin (hCG), which helps to maintain the lining of the uterus. It also sends a signal to the ovary to stop releasing an egg each month, which stops your monthly periods.

hCG is the hormone that's measured in pregnancy tests. This week, a pregnancy test probably could detect your pregnancy. hCG also causes the symptoms of pregnancy, which might start now. Tiredness, tingling or aching breasts, or nausea also can happen with premenstrual syndrome (PMS). But by the end of this week, your period won't happen. Instead, your pregnancy is under way!

Week 5

Your baby's development

Until now, the embryo has been a mass of cells. But now a distinct shape begins to form. The neural tube (which will become the spinal cord and brain) runs from the top to the bottom of the embryo. A bulge in the center of the embryo will develop into your baby's heart.

At this time, the placenta develops. It's through the placenta and its fingerlike projections, called chorionic villi, that an embryo gets nourishment from its mother.

Your Body

Even if nausea hasn't hit you yet, you'll want to steer clear of some foods. Foodborne illnesses, such as listeriosis and toxoplasmosis, may cause birth defects or even miscarriage.

Here are some foods to avoid:

soft, unpasteurized cheeses (often advertised as "fresh") such as feta, goat, Brie, Camembert, and blue cheese
unpasteurized milk, juices, and apple cider
raw eggs or foods containing raw eggs, including mousse and tiramisu
raw or undercooked meats, fish, or shellfish
processed meats such as hot dogs and deli meats (if you eat them, they should be well-cooked)
fish high in mercury, including shark, swordfish, king mackeral, or tilefish

Toxoplasmosis also can spread from soiled cat litter boxes, so try to have someone else clean the litter box during your pregnancy.

Week 6

Your baby's development

By week 6, your baby's brain and nervous system are developing quickly. Optic vesicles, which later form the eyes, begin to develop on the sides of the head, as do the passageways that will make up the inner ear.

Your baby's heart will begin to beat around this time, and might even be detected on ultrasound examination. And the beginnings of the digestive and respiratory systems are forming too. Small buds that will grow into your baby's arms and legs appear this week.

Because their legs are curled up against the torso for much of the pregnancy, making a full-length measurement difficult, babies often are measured from the crown to rump (from the top of the head to bottom the buttocks) rather than from head to toe. This week, your baby only measures 0.08 to 0.2 inches (2 to 5 millimeters) from crown to rump!

Your Body

Common pregnancy complaints might hit with full force this week. You may feel very tired as your body adjusts to the demands of pregnancy. And tender, aching breasts and nausea and vomiting (morning sickness) may leave you feeling less than great. Despite its name, morning sickness can happen at any hour or all day, so don't be surprised if your queasy stomach doesn't pass by noon.

Nausea isn't the only thing that might have you running to the bathroom — hormonal changes and other things, such as your kidneys working extra hard to flush wastes out of your body, can make you need to pee more often too.

Week 7

Your baby's development

By this week, the umbilical cord has formed. It will be your baby's connection to you during your pregnancy, providing oxygen and nourishment for your baby and disposing of wastes. Your baby's digestive tract and lungs continue to form.

Are you longing to see your baby's face on his or her birth day? You have a long way to go until then, but your baby's face is taking shape. The mouth, nostrils, ears, and eyes are some of the facial features that become more defined this week.

Dreaming of a son or daughter to play ball with? The arm bud that developed just last week has a hand on the end of it, which looks like a tiny paddle.

Your Body

Pregnancy causes many changes in your cervix. By this week you'll have developed a mucus plug, which forms in the opening of the cervical canal and seals off the uterus to protect it from infection. (You'll lose this plug later when your cervix dilates in preparation for labor.)

Week 8

Your baby's development

Marveling over a baby's tiny fingers and toes is one of the joys of the first day of life. Those fingers and toes are just beginning to form this week, and the arms can even flex at the elbows and wrists. The eyes are becoming more obvious because they've begun to develop pigment (color) in the retina (back of the eye).

Also, the intestines are getting longer and there isn't enough room for them in the baby's abdomen, so they protrude into the umbilical cord until week 12.

By now, the beginnings of the buds that will develop into your baby's genitals have made their appearance, although they've not yet developed enough to reveal whether your baby is a boy or a girl.

Your Body

Pregnancy symptoms such as a missed period, nausea, extreme fatigue, or tight clothes due to the swelling of your uterus have probably prompted you to wonder whether you're pregnant. Once you have confirmation of your pregnancy from a home pregnancy test or blood or urine test at the doctor's office, schedule your first prenatal visit.

Good prenatal care is extremely important for the health and safe delivery of your baby, so be sure to make prenatal appointments a top priority. If your pregnancy is considered high-risk (for example, if you have had multiple miscarriages, are older than 35, or have a history of pregnancy complications), your doctor may want to see you as early as possible and more often during the course of your pregnancy.

Week 9

Your baby's development

The tail at the bottom of your baby's spinal cord has shrunk and almost disappeared by this week. In contrast, your baby's head has been growing — it's quite large compared with the rest of the body and it curves onto the chest.

By this week, your baby measures about 0.6 to 0.7 inches (16 to 18 millimeters) from crown to rump and weighs around 0.1 ounces (3 grams). The tip of the nose has developed and can be seen in profile, and flaps of skin over the eyes have begun to shape into eyelids, which will become more noticeable in the next few weeks.

The digestive system continues to develop. The anus is forming, and the intestines are growing longer. Internal reproductive features, such as testes and ovaries, start to form this week.

Your baby may make some first movements this week as muscles develop. If you had an ultrasound now, those movements might even be visible, but you won't be able to feel them for several more weeks.

Your Body

In preparation for your first prenatal visit, take the time to familiarize yourself with your family's health history and to review your medical records. Have you had any chronic illnesses, allergies, or surgeries? Are you taking any prescription medicines? Do you know of any genetic disorders that run in your family? Has your menstrual cycle been regular, and have you had any past pregnancies? What are your exercise habits? These are some of the things your health care provider will want to discuss with you, so it will help to have this information ready when you go.

Week 10

Your baby's development

By week 10, all of your baby's vital organs have been formed and are starting to work together.

As external changes (such as the separation of fingers and toes and the disappearance of the tail) happen, internal developments do too. Tooth buds form inside the mouth, and if you're having a boy, his testes will begin producing the male hormone testosterone.

Congenital abnormalities are unlikely to develop after week 10. This also marks the end of the embryonic period — in general, the embryo now has a distinctly human appearance. Starting next week, your baby will officially be considered a fetus.

Your Body

Your first prenatal visit, which often takes place around this time, is a milestone. At the doctor's office, you'll go through a series of tests and checks, including having your weight and blood pressure checked. You might also have an external abdominal examination to check the size and position of your baby and have your urine tested.

During the visit, your health care provider (who could be an obstetrician, family doctor, midwife, or nurse practitioner) will do a thorough examination. This includes an internal exam and a breast exam. Your health care provider will also ask you many questions about your medical history and any family health problems. This can help determine if your baby is at risk for genetic diseases.

Another thing your provider will check? Your baby's heartbeat! Using a Doppler stethoscope, you should get to hear it for the first time.

Your provider will probably send you for a blood test to find out whether you're immunized against varicella, measles, mumps, and rubella (German measles), and to find out your blood type and Rh factor. You also may be tested for certain infections, such as syphilis or hepatitis B, and you may be offered an HIV test.

Testing blood for certain genetic disorders is also commonly done — the type of tests offered will depend on your situation and preference.

Week 11

Your baby's development

From this week until week 20, your baby will be growing quickly — increasing in size from about 2 inches (5 cm) to about 8 inches (20 cm) from crown to rump. To handle all this growth, the blood vessels in the placenta are growing in both size and number to provide your baby with more nutrients.

Facial development continues as the ears move toward their final position on the sides of the head. If you saw a picture of your baby now, you'd think you had a genius on your hands — the baby's head accounts for about half of the body length!

Although your baby's reproductive organs are developing rapidly, the external genitals of boys and girls appear somewhat similar until the end of week 11. They will be clearly differentiated by week 14.

Your Body

Nourishing your baby usually requires that you gain weight — and in most cases, the recommended weight gain is 25 to 35 pounds (11.33 to 15.87 kg) over the course of the pregnancy. If you were overweight or underweight before pregnancy, your health care provider may have different recommendations for weight gain.

Your health care provider may offer you a "first trimester screening test." This combines an ultrasound with a blood test to see whether your baby is at risk for (not whether your baby has) a chromosomal abnormality. An abnormal result does not necessarily mean that your baby has a condition — but more testing might be needed. Talk to your health care provider about the risks and advantages of this test.

Week 12

Your baby's development

Your baby's brain continues to develop, and tiny fingernails and toenails start to form.

Your baby's kidneys are functioning! After swallowing amniotic fluid, your baby will now be able to pass it out of the body as urine (pee). And the intestines will make their way into the abdomen because there is room for them now.

Your body

Has anyone told you that you have that "pregnancy glow"? It's not just from the joy you may feel because you're having a baby — there's a physical reason for smoother, more radiant skin during pregnancy. Increased blood volume and pregnancy hormones work together to give you that glow. The greater blood volume brings more blood to the blood vessels and the hormones increase oil gland secretion, making skin look flushed, plumper, and smoother. Sometimes, though, the increased oil gland secretion can cause temporary acne.

Second trimester

Week 13

Your baby's development

Welcome to the second trimester of pregnancy! Your placenta has developed and is providing your baby with oxygen, nutrients, and waste disposal. The placenta also makes the hormones progesterone and estrogen, which help to maintain the pregnancy.

By now, the baby's eyelids have fused together to protect the eyes as they develop. Once you take your newborn home, you might be wishing for those eyes to close once in a while so you can get some rest!

Your baby might be able to put a thumb in his or her mouth this week, although the sucking muscles aren't completely developed yet.

Your body

At your first prenatal appointment, your health care provider probably gave you a prescription for prenatal vitamins. Taking these supplements, in addition to eating a healthy diet, ensures your baby gets needed vitamins and minerals, such as folic acid, zinc, iron, and calcium, which aid growth and development. Talk to your pharmacist about the best way to take your vitamins (such as whether they should be taken with food).

Week 14

Your baby's development

By this week, some fine hairs have developed on your baby's face. This soft colorless hair is called lanugo, and it will eventually cover most of your baby's body until it's shed just before delivery.

By now, your baby's genitals have fully developed, though they may still be difficult to detect on an ultrasound. Your baby also starts to produce thyroid hormones because the thyroid gland has matured.

Your baby now weighs about 1.6 ounces (45 grams) and is about 3.5 inches (9 cm) long from crown to rump.

Your body

Your health care provider may discuss amniocentesis with you if you're older than 35 or if your screening tests indicated that there may be a problem with the fetus. Amniocentesis is a test usually done between 15 and 18 weeks that can detect abnormalities in a fetus, such as Down syndrome.

During this test, a very thin needle is inserted into the amniotic fluid surrounding the baby to take a sample of the fluid for analysis. Amniocentesis does carry a very slight risk of miscarriage, so talk to your health care provider about your concerns and the risks and advantages of the test.

Week 15

Your baby's development

Parents are often amazed by the softness of their newborn's skin. Your baby's skin has been continuously developing, and is so thin and translucent that the blood vessels are visible through it. Hair growth continues on the eyebrows and the head. Your baby's ears are almost in position now, although they're still a bit low on the head.

Your baby's skeletal system continues to develop. Muscle development continues too, and your baby is probably making lots of movements with the head, mouth, arms, wrists, hands, legs, and feet.

Your body

Has it sunk in yet that you're pregnant? Many women say that it isn't until they trade in their jeans for maternity clothes and other people start noticing their swelling abdomens that the reality of pregnancy sets in. For many, this realization is both joyful and scary.

It's normal to feel as if you're on an emotional roller coaster (you have your hormones to thank). Another thing you may be feeling? Scatterbrained. Even the most organized women report that pregnancy somehow makes them forgetful, clumsy, and unable to concentrate. Try to keep the stress in your life to a minimum and take your "mental lapses" in stride — they're only temporary.

Week 16

Your baby's development

Your baby now weighs about 3.9 ounces (110 grams) and measures about 4.7 inches (12 cm) in length from crown to rump. Your baby can hold his or her head erect, and the development of facial muscles allows for a variety of expressions, such as squinting and frowning.

Your body

Between weeks 16 and 18 of pregnancy, your health care provider may offer you a second trimester screening test (known as the multiple marker test or triple screen). This test measures the levels of alpha-fetoprotein (AFP), a protein produced by the fetus, and the pregnancy hormones hCG and estriol in the mother's blood. It's called a quadruple screen (or quad screen) when the level of an additional substance, called inhibin-A, is also measured.

If you have already done a blood test and/or ultrasound in the first trimester (first trimester screening test), then the results of the two tests together is called an integrated screening test. The results of these tests can tell moms whether their babies are at risk for (not whether they have) neural tube defects such as spina bifida or chromosomal abnormalities such as Down syndrome.

An abnormal result does not necessarily mean that your baby has a problem — but it may mean more testing is required. Talk to your health care provider about the risks and advantages of these tests.

Week 17

Your baby's development

At about 5.1 inches (13 cm) from crown to rump and weighing 4.9 ounces (140 grams), your baby is still very tiny.

The placenta, which nourishes the fetus with nutrients and oxygen and removes wastes, is growing to accommodate your baby. It now contains thousands of blood vessels that bring nutrients and oxygen from your body to your baby's developing body.

Your body

You may notice that your breasts have changed considerably since your pregnancy began. Hormones are preparing your breasts for milk production — more blood is flowing to the breasts, and the glands that produce milk are growing in preparation for breastfeeding. This can increase your breast size (many women increase one to two cup sizes) and make veins become visible. Buy supportive bras in a few different sizes to manage your breast growth during pregnancy.

Week 18

Your baby's development

Ears move to their final position and they stand out from the head. And start brushing up on your lullabies — in the coming weeks, your baby will probably be able to hear! The bones of the middle ear and the nerve endings from the brain are developing so that your baby will hear sounds such as your heartbeat and blood moving through the umbilical cord. He or she may even be startled by loud noises!

Your baby's eyes are also developing — they're now facing forward rather than to the sides, and the retinas may be able to detect the beam of a flashlight if you hold it to your abdomen.

Until now, your baby's bones had been developing but were still soft. This week, they begin to harden, or ossify. Some of the first bones to ossify are those in the clavicles and the legs.

Your body

You're probably beginning to prepare for life with baby. This is a good week to begin your search for a pediatrician or other health care provider for your child. Schedule visits to meet with potential doctors to discuss issues such as appointment availability and when to call in an emergency.

You'll also want to learn as much as you can about their practices and procedures. Some good questions to ask: How many health care providers are in the practice? Who covers nights and weekends? What is their policy on phone calls? Which hospitals are they affiliated with? What insurance do they accept? What specialists do they work with? How are emergencies handled?

It's important that you feel comfortable with your child's doctor, so do your homework and make your decision carefully.

Week 19

Your baby's development

Your baby is now covered with a white, waxy substance called vernix caseosa, which helps prevent delicate skin from becoming chapped or scratched. Premature babies may be covered in this cheesy coating at delivery.

Your baby is still tiny, but this week brings the development of brown fat, which will help keep your baby warm after birth. During the last trimester, your baby will add more layers of fat for warmth and protection.

Your body

You might feel your baby's first movements. This often happens between weeks 18 and 20. These first movements are known as quickening, and they may feel like butterflies in your stomach or a growling stomach. Later in your pregnancy, you'll feel kicks, punches, and possibly hiccups! Each baby has different movement patterns, but if you're concerned or if the movements have decreased in frequency or intensity, talk to your doctor.

Many women wonder around this time whether having sex will hurt their developing baby, and the answer is no. Sex is considered safe at all stages of pregnancy, as long as your pregnancy is normal. But that doesn't necessarily mean you're going to want to have it. Many expectant women find that their desire for sex fluctuates during the various stages of pregnancy, depending on their fatigue, growing size, anxiousness over the birth, and a host of other body changes. Keep the lines of communication with your partner open as these issues come up. Even though you may both be preoccupied with the baby, it's also important to have some "together time."

Week 20

Your baby's development

You're halfway there! Twenty weeks into your pregnancy, your baby has grown significantly from that first dividing cell and now weighs about 11 ounces (312 grams) and measures about 6.3 inches (16 cm) from crown to rump. The baby is taking up increasing room in your uterus, and continued growth will put pressure on your lungs, stomach, bladder, and kidneys.

Under the vernix caseosa (a protective, waxy coating), your baby's skin is thickening and developing layers. Hair and nail growth continue.

Your body

If you haven't already had one, your health care provider may recommend that you receive an ultrasound, a diagnostic test that uses sound waves to create an image. An ultrasound can determine the size and position of the fetus, and any structural abnormalities of bones and organs that are visible by this time. Depending on the position of the fetus, the sex can usually be determined by now. During an ultrasound, the umbilical cord, placenta, and amniotic fluid can also be examined. Talk to your health care provider about whether you should have this test.

Week 21

Your baby's development

The amniotic fluid that has cushioned and supported your baby now serves another purpose. The intestines have developed enough that small amounts of sugars can be absorbed from the amniotic fluid that your baby swallows and passed through the digestive system to the large bowel. Almost all of your baby's nourishment, however, still comes from you through the placenta.

Until now, your baby's liver and spleen have been responsible for making blood cells. But now the bone marrow spaces are developed enough to contribute to blood cell formation. Bone marrow will become the major site of that production in the third trimester and after birth. (The spleen will stop producing blood cells by week 30, and the liver will stop a few weeks before birth.)

Your body

Is exercise safe during pregnancy? Exercise can be a great way to stay in shape during pregnancy and can even keep some problems — such as varicose veins, excessive weight gain, and backache — to a minimum.

But pregnancy is not the time to start training for a triathlon — going slowly is the name of the game. Because ligaments become more relaxed during pregnancy, you're at higher risk for injury, so low- or non-impact exercise such as yoga, swimming, and walking are your best bets. Talk to your health care provider before beginning any exercise program while you're pregnant.

Week 22

Your baby's development

The senses your baby will use to learn about the world are developing daily. Taste buds have started to form on the tongue, and the brain and nerve endings are formed enough so that the fetus can feel touch. Your baby may experiment with this newfound sense by stroking his or her face or sucking on a thumb, as well as feeling other body parts and seeing how they move.

Your baby's reproductive system continues to develop. In boys, the testes have begun to descend from the abdomen, and in girls, the uterus and ovaries are in place and the vagina is developed.

Your body

If you haven't felt them already, you may soon notice your uterus practicing for delivery with irregular, painless contractions called Braxton Hicks contractions. You may feel a squeezing sensation in your abdomen. Don't worry, though: Your baby may be able to feel the contraction as it squeezes the uterus, but these aren't dangerous or harmful.

But if the contractions become more intense, painful, or frequent, contact your health care provider immediately because painful, regular contractions may be a sign of preterm labor.

Week 23

Your baby's development

Even though fat is beginning to build up on your baby's body, the skin still hangs loosely, giving your baby a wrinkled appearance. Your baby's daily workout routine includes moving the muscles in the fingers, toes, arms, and legs regularly. As a result, you may feel more forceful movements.

By now your baby weighs a little more than 1 pound (454 grams). If preterm labor and delivery happened this week, a baby could survive with expert medical care, but might have mild to severe disabilities. With increasing research and knowledge in the field of fetal medicine, the long-term prognosis for premature babies (preemies) improves every year.

Your body

The closer you get to your delivery date, the more trouble you may have sleeping. Anxiety, getting up to pee, heartburn, leg cramps, and general discomfort can mean a short night's sleep. But your baby's health and your own depend on you getting enough rest. Try a warm bath, soothing music, a relaxing book, or a cup of herbal tea to put you in the mood to snooze.

Many doctors recommend that pregnant women sleep on their sides, not their backs or stomachs, so that blood flow to the placenta is not restricted. If you find this uncomfortable, try placing a pillow between your knees to relieve the pressure of your weight while lying on your side.

Week 24

Your baby's development

Because the inner ear — which controls balance — is now completely developed, your baby might be able to tell when he or she is upside down or right side up while floating and making movements in the amniotic fluid.

Your body

An important prenatal test, glucose screening, is usually done sometime between weeks 24 and 28. This test checks for gestational diabetes, a temporary type of diabetes during pregnancy that can cause problems in a newborn, such as low blood sugar. Gestational diabetes can make a woman more likely to need a C-section because it can lead to the growth of very large babies.

For the glucose screening test, you'll drink a sugary solution and then have your blood drawn. If your blood sugar levels are too high, you'll have more tests, which your health care provider will discuss with you. Gestational diabetes usually can be controlled with a well-planned diet and regular exercise, but some pregnant women will need medicine, such as daily insulin, during the pregnancy.

Week 25

Your baby's development

You may notice that your baby has resting and alert periods. You'll notice fetal activity more readily when you are still or relaxing. Your baby's hearing has continued to develop too — he or she may now be able to hear your voice!

Your body

Pregnancy can cause some unpleasant side effects when it comes to digestion. Not only does the hormone progesterone slow the emptying of the stomach — it also relaxes the valve at the entrance to the stomach so that it doesn't close properly. This lets acidic stomach contents move upward into the esophagus. The result: reflux (also known as heartburn) that can make eating your favorite meals a nightmare.

The expanding uterus puts additional pressure on the stomach in the last few months of pregnancy. Try eating smaller, more frequent meals, and avoid spicy and fatty foods.

Week 26

Your baby's development

Your baby's eyes have been sealed shut for the last few months, but they'll soon open and begin to blink. Depending on ethnicity, some babies will be born with blue or gray-blue eyes (which may change color in the first year of life) and some will be born with brown or dark eyes. Eyelashes are growing in, as is more hair on the head.

Your baby, weighing a little less than 2 pounds (907 grams), still looks wrinkly but will continue to gain weight steadily over the next 14 weeks until birth.

Your body

Your uterus provides a safe haven for your baby before birth. But what about after delivery? Your baby will be moving about your home in what seems like no time at all. Take the time now to safeguard your home by babyproofing. Covering electrical outlets, removing choking hazards, installing smoke alarms, and blocking off staircases are just some of the steps to ensuring your child's safety. Take every precaution you can think of, but remember: No amount of babyproofing can substitute for careful supervision of your child.

Third trimester

Week 27

Your baby's development

By this first week of the third trimester, your baby looks similar to what he or she will look like at birth, just thinner and smaller. The lungs, liver, and immune system still need to fully mature, but if born now, your baby would have a very good chance of surviving.

As hearing continues to develop, your baby may start to recognize your voice as well as your partner's. Sounds may be muffled, though, because the ears are still covered with vernix, the thick waxy coating that protects the skin from becoming chapped by the amniotic fluid.

Your body

Your body continues to protect and nourish your baby. But what happens when it's time to meet your little one? Consider signing up for childbirth classes through your local community center or hospital to learn about labor, options for pain relief, and what to expect after delivery. You'll also learn about common newborn problems, babyproofing, breastfeeding and formula feeding, and infant CPR. Learning all you can about birth and babies will help you feel more confident, especially if you're a first-time parent.

Week 28

Your baby's development

Your baby now weighs about 2 pounds, 2 ounces (1,000 grams) and measures about 10 inches (25 cm) from crown to rump. The folds and grooves of your baby's brain are still developing and expanding, and your baby's adding layers of fat.

At your next prenatal appointment, your health care provider may tell you whether your baby is headfirst or feet- or bottom-first (called breech position) in the womb. Babies who are in the breech position may need to be delivered by C-section. Your baby still has 2 months to change position, though, so don't worry if your baby is in the breech position right now. Most babies will switch positions on their own.

Your body

Your health care provider probably sent you for some blood tests early in your pregnancy. One thing blood tests measure is the Rh factor, a substance found in the red blood cells of most people. If you don't have it (if you're Rh negative) but your baby does (is Rh positive), there's the potential for your baby to have health problems, such as jaundice and anemia. Your doctor can prevent these problems by giving you Rh immune globulin shots this week and again after delivery.

Week 29

Your baby's development

Your baby continues to be active, and those first few flutters of movement have given way to hard jabs and punches that may take your breath away. If you notice a decrease in movement, do a fetal kick count: Your baby should move at least 10 times in 2 hours. If your baby moves less, talk to your health care provider.

Your body

During pregnancy, iron is important for replenishing the red blood cell supply. You should be eating at least 30 milligrams of iron each day. Because iron deficiency is common during pregnancy, your health care provider may recommend that you have a blood test to check your iron level. If it's low, you may be prescribed an iron supplement.

Week 30

Your baby's development

Now weighing about 3 pounds (1,400 grams) and measuring about 10.8 inches (27 cm) from crown to rump, your baby continues to gain weight and add layers of fat. This fat makes the baby look less wrinkly and will help provide warmth after birth.

To prepare for breathing after birth, your baby will mimic breathing movements by repeatedly moving the diaphragm. Your baby can even get hiccups, which you may feel as rhythmic twitches in your uterus.

Your body

Constipation is a common complaint of pregnancy. Pregnancy hormones slow the digestive process considerably. Exercising regularly and eating high-fiber foods, like vegetables and whole grains, are great ways to keep everything regular.

Week 31

Your baby's development

Your baby is peeing several cups of urine a day into the amniotic fluid. He or she is also swallowing amniotic fluid, which is replaced completely several times a day.

Too much fluid in the amniotic sac (polyhydramnios) could mean that the baby isn't swallowing normally or that there's a gastrointestinal obstruction. Not enough fluid in the amniotic sac (oligohydramnios) could mean that the baby isn't peeing properly, which could indicate a problem with the kidneys or urinary tract. Your health care provider will measure your levels of amniotic fluid as part of your routine ultrasound.

Your body

Have you decided whether to breastfeed or formula feed your baby? Experts recommend breast milk as the best form of infant nutrition, but the decision about how to feed your baby is a personal one. Talk to your health care provider or a lactation consultant if you need more information before making your choice.

The milk glands in your breasts may have started to make colostrum by now. Colostrum is the pre-milk that provides your baby with calories and nutrients for the first few days before your milk comes in (if you plan to breastfeed). For some women, it is thin and watery. For others, it is thick and yellowish. If you notice your breasts leaking colostrum, you can buy disposable or washable breast pads to protect your clothing.

Week 32

Your baby's development

The final touches are being placed on your baby masterpiece. Eyelashes, eyebrows, and the hair on your baby's head are evident. The lanugo hair that has covered your baby since the beginning of the second trimester is falling off, although some may remain on the shoulders and back at birth.

At about 4 pounds (1,800 grams) and 11.4 inches (29 cm) from crown to rump, your baby would have an excellent chance of survival outside the womb if you delivered now.

Your body

During your prenatal visits, your health care provider will monitor your blood pressure, urine, and any swelling that may develop. But symptoms such as sudden weight gain, swelling in the hands or face, headaches, or changes in vision can be signs of preeclampsia. This condition causes high blood pressure and protein in the urine. Tell your health care provider right away if you have any of these symptoms.

Week 33

Your baby's development

In these last few weeks before delivery, the billions of developed neurons in your baby's brain are helping him or her to learn about the in-utero environment — your baby can listen, feel, and even see somewhat. Your baby's eyes can detect light and the pupils can constrict and dilate in response to it.

Like a newborn, your baby sleeps much of the time and even has rapid eye movement (REM) sleep, the sleep stage during which our most vivid dreams happen!

Your baby's lungs are almost completely matured. Fat will continue to build on your baby's body for protection and warmth. Babies gain a good deal of their weight in the final few weeks before birth.

Your body

With labor and delivery only 2 months away, you may be considering how you'll cope with pain during childbirth. Commonly used ways to help manage pain include breathing techniques such as those taught in Lamaze classes; pain-relief medicines given through injection; and epidurals, where doctors can give an anesthetic through a soft, thin catheter placed in the lower back.

Whatever your choice, the more you know, the better informed your decision will be. You don't have to decide yet, but discuss your choices with your health care provider soon.

Week 34

Your baby's development

Maternal calcium intake is very important during pregnancy. A developing baby draws calcium from the mother to make and harden bone. Because your growing baby's calcium demands are high, be sure you're getting enough of this mineral to prevent a loss of calcium from your own bones. Your prenatal vitamin has some extra calcium, but be sure to also eat calcium-rich foods like milk and other dairy products, tofu, broccoli, and calcium-fortified juices and foods.

By now most babies will be in position for delivery. Your health care provider can tell you if your baby is positioned head- or bottom-first. Babies born at 34 weeks usually have fairly well-developed lungs, and their average size of 5 pounds (2,250 grams) and 12.6 inches (32 cm) from crown to rump allows them to survive outside the womb without extensive medical intervention.

Your body

Being tired is a common complaint of late pregnancy. Difficulty sleeping, aches and pains, weight gain, and anxiety about labor, delivery, and taking care of a newborn may contribute to your exhaustion. Rest as much as you can and take naps if possible.

Week 35

Your baby's development

This week begins your baby's most rapid period of weight gain — about 8 to 12 ounces (226 to 340 grams) each week! Fat is being deposited all over your baby's body, especially around the shoulders. The vernix coating on the baby's skin is becoming thicker, whereas lanugo hair is almost completely gone.

This increasing size means that your baby is now cramped and restricted inside the uterus — you might feel fewer movements, but they may be stronger and more forceful. If in a headfirst position, your baby's head will rest on your pubic bone in preparation for labor.

Your body

Your bond with your baby will be even stronger once your little one is here. Bonding doesn't only happen right after birth. It may happen later or develop over time. Bonding makes parents want to protect their baby and shower him or her with affection, and it builds a baby's sense of security.

Week 36

Your baby's development

The tiny wrinkly fetus you saw on earlier ultrasounds is fast becoming a plump baby. Fat on the cheeks and powerful sucking muscles contribute to your baby's fuller face. Your baby now weighs a little under 6 pounds (2,721 grams).

The bones that make up your baby's skull can move and overlap each other. This is called molding, and it helps the baby pass through the birth canal. Don't be surprised if your little one arrives with a pointy or misshapen head! After a few hours or days, your baby's head will be back to a rounded shape.

Your body

You now might see your health care provider every week. Your doctor or midwife may do an internal exam to see if cervical effacement (thinning of the cervix) or dilation (opening of the cervix) has begun. The baby might drop into your pelvis in preparation for labor — this is called engagement or lightening. Your appetite may return because the baby isn't putting as much pressure on your stomach and intestines, and if you've had heartburn, that might ease.

Week 37

Your baby's development

By now, your baby has developed enough coordination to grasp with the fingers. If shown a bright light, your baby may turn toward it in your uterus.

He or she continues to gain weight — developing fat at the rate of half an ounce (14 grams) a day. In general, boys weigh more than girls at birth.

Your body

After this week, you may lose the mucus plug that sealed off your uterus to protect it from infection. The mucus plug (which can be lost a few weeks, days, or hours before labor) can be clear, pink, yellowish, or tinged with blood (this is called "the bloody show"). As the cervix dilates in preparation for birth, the plug is discharged from the body. Be sure to speak with your health care provider about any discharge you have.

Week 38

Your baby's development

Your baby weighs about 6 pounds, 6 ounces (2,900 grams) now and measures about 13.4 inches (34 cm) in length from crown to rump. Fat is still building, although growth is slower now. You may notice that your weight gain has slowed or stopped.

Your baby has been able to suck and swallow amniotic fluid, so waste material has built up in the intestines. Cells shed from the intestines, dead skin cells, and lanugo hair are some of the waste products that make meconium, a greenish-black substance that is your baby's first bowel movement.

If you're having a boy, his testicles have dropped into the scrotum, unless he has a condition called undescended testicle. If you're having a girl, the labia are now completely developed.

Your body

Because your baby is engaged in your pelvis, your bladder is very compressed, making frequent bathroom trips a necessity.

If you're having a boy, have you and your partner made a decision about circumcision? This surgical procedure removes the foreskin of the penis in male babies. For some parents, the decision about whether to circumcise is easy; for others, it's not. Talk to your health care provider about the issues surrounding circumcision, including pain relief options for the baby.

Week 39

Your baby's development

Umbilical cords usually are about 22 inches (55 cm) long and half an inch (1–2 cm) thick. Sometimes, the cord can get wrapped around a baby's neck. This usually won't be a problem unless it puts pressure on the cord during labor or delivery. In that case, a woman might need a C-section. A true knot in the umbilical cord happens much less often (in about 1% of pregnancies).

Most of the vernix that covered your baby's skin has disappeared, as has the lanugo. Your body has been supplying the baby with antibodies through the placenta that will help your little one's immune system fight infection for the first 6–12 months of life.

Your body

Braxton Hicks contractions may become more pronounced. Also called "false labor," these contractions may be as painful and strong as true labor contractions, but don't become regular or increase in frequency as true contractions do.

Another sign of labor, the rupture of the amniotic sac's membranes (when your "water breaks"), could happen any day now. Some women have a large gush of water, while others feel a steady trickle. Often, a woman's water doesn't break until she's well into labor. To start or speed up their labor, some women will need to have the membranes ruptured by their health care provider.

If you think your water has broken or you're having regular contractions, call your health care provider.

Week 40

You Baby's Development

After months of anticipation and preparation, your baby is here! Or maybe not — most women don't deliver right on their estimated due dates. Many first-time moms find themselves waiting up to 2 weeks after their due date for their baby to arrive.

A baby born at 40 weeks weighs, on average, about 7 pounds, 4 ounces (3,300 grams) and measures about 20 inches (51 cm).

Don't expect your baby to look picture perfect right away, though — a newborn's head often is temporarily misshapen from the birth canal and may be covered with vernix and blood. Your baby's skin might have discolorations, dry patches, and rashes. This is all completely normal.

Right after birth, your health care provider will suction mucus out of your baby's mouth and nose, and you'll hear that long-awaited first cry. Your baby may then be placed on your stomach, and the umbilical cord will be cut — often by the baby's dad, if he chooses to do the honors!

A series of quick screening tests, such as the Apgar score, will assess your baby's vital signs and responsiveness. Then your little one be weighed and measured.

If you had a high-risk pregnancy or a C-section, a neonatologist (a doctor who specializes in newborn intensive care) will be at your delivery to take care of your baby right away. Your baby will receive any special care needed to adjust to life outside the womb — and then will be placed in your waiting arms.

Your body

This week is the moment you've been waiting for — you meet your baby! Before you do, though, you have to go through labor and delivery. You may have learned about the three stages of birth in your prenatal classes. The first stage of labor works to thin and stretch the cervix by contracting your uterus at regular intervals. The second stage is when you push your baby into the vaginal canal and out of your body. The third and final stage of labor is when you deliver the placenta.

If you don't go into labor within a week of your due date, your health care provider may recommend you have a nonstress test. This monitors fetal heart rate and movement to be sure that the baby is getting enough oxygen and that the nervous system is responding. Your health care provider will tell you more about this test, if it's needed.

If your labor isn't progressing, or if your health or your baby's health requires it, your health care provider may induce labor by artificially rupturing the membranes (breaking your water) or by giving you the hormone oxytocin or other medicines. A high-risk pregnancy or other potential complications may require a C-section delivery.

Some women know ahead of time that they'll deliver via C-section so can schedule and prepare for their baby's "birth day" in advance. This might help to ease feelings of disappointment that moms who can't deliver vaginally sometimes have.

If you had a C-section that wasn't planned, you may feel a little sad. Remember that having a C-section does not make your baby's birth any less special or your efforts any less amazing. After all, you went through major surgery to deliver your baby!

Congratulations and best of luck with your baby!

Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor.

Images provided by The Nemours Foundation.

What to Expect Week-by-Week

A Word About Due Dates and Trimesters

Getting Started

First trimester

Week 1

Week 2

Week 3

Week 4

Week 5

Week 6

Week 7

Week 8

Week 9

Week 10

Week 11

Week 12

Second trimester

Week 13

Week 14

Week 15

Week 16

Week 17

Week 18

Week 19

Week 20

Week 21

Week 22

Week 23

Week 24

Week 25

Week 26

Third trimester

Week 27

Week 28

Week 29

Week 30

Week 31

Week 32

Week 33

Week 34

Week 35

Week 36

Week 37

Week 38

Week 39

Week 40

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