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What Are Prenatal Tests?

Prenatal tests are screening or diagnostic tests that can help identify health problems that could affect pregnant women or their unborn babies. Some of these conditions can be treated, so it's important to find them as soon as possible.

Why Are Prenatal Tests Done?

Prenatal tests are given in the first, second, and third trimesters. In a mother, they can determine key things about her health that can affect her baby's health, such as:

  • her blood type
  • whether she has gestational diabetes, anemia, or other health conditions
  • her immunity to some diseases
  • whether she has a sexually transmitted disease (STD) or cervical cancer

In a developing child, prenatal tests can:

  • identify treatable health problems that can affect the baby
  • show characteristics of the baby, including size, sex, age, and position in the uterus
  • help determine whether a baby might have a birth defect, genetic problem, or other condition

Some prenatal tests are screening tests that can only reveal the possibility of a problem. Other prenatal tests are diagnostic tests that can accurately find whether a fetus has a specific problem. A screening test sometimes is followed by a diagnostic test.

Although your health care provider (who may be your OB-GYN, family doctor, or a certified nurse-midwife) may recommend these tests, it's up to you to decide whether to have them.

Think you might need prenatal tests? It's a good time to schedule a prenatal consultation

Who Should Have Prenatal Tests?

Some prenatal tests are considered routine — that is, almost all pregnant women receiving prenatal care get them. They include things like checking urine (pee) levels for protein, sugar, or signs of infection.

Other non-routine tests are recommended only for some women, especially those with high-risk pregnancies. These may include women who:

  • are age 35 or older
  • are teens
  • have had a premature baby
  • have had a baby with a birth defect (especially heart or genetic problems)
  • are carrying more than one baby
  • have high blood pressure, diabetes, lupus, heart disease, kidney problems, cancer, an STD, asthma, or a seizure disorder
  • have an ethnic background in which genetic disorders are common (or a partner who does)

Where Else Should I Know?

Remember that tests are offered to you — it's your choice whether to have them.

To decide which tests are right for you, talk with your health care provider about why a test is recommended, its risks and benefits, and what the results can — and can't — tell you.

Questions to ask:

  • How accurate is this test?
  • What does it measure?
  • What do you hope to learn from the test results?
  • Is the procedure painful?
  • Could it be dangerous to me or the baby?
  • Do the potential benefits outweigh the risks?
  • When will I get the results?
  • What are my options if the results indicate a problem?
  • What could happen if I don't have this test?
  • How much will the test cost?
  • Is the test covered by insurance?
  • How should I prepare for the test?
Reviewed by: Elana Pearl Ben-Joseph, MD
Date reviewed: February 2018

First trimester

Prenatal tests can offer valuable information about your health during pregnancy. They can find problems like gestational diabetes and preeclampsia (dangerously high blood pressure), which if not treated can put your baby at risk for problems like preterm birth.

Tests can also tell you things about your baby's health, like whether your child has a birth defect or a chromosomal abnormality. Of course, no test is foolproof. Results can be inaccurate, but the chances of this happening are low.

If your doctor recommends a screening or test, be sure to learn about the risks and benefits. Most parents agree that prenatal tests offer them peace of mind while helping to prepare them for their baby's arrival. But it's your choice to accept or decline a test.

Read on to learn about tests that may be available to you during your first trimester.

First-Visit Screenings & Tests

One of the goals of your first visit to the obstetrician's office is to confirm your pregnancy and determine whether you or your baby is at risk for any health problems.

The doctor will give you a full physical, which may include a weight assessment, blood pressure check, and breast and pelvic examination. If you're due for your routine cervical test (Pap smear), the doctor will perform it during the pelvic exam. This test detects changes in your cervical cells that could lead to cancer.

To do a Pap smear, the inside of your cervix (the opening to the uterus that's located at the very top of the vagina) will be swabbed with a cotton swab. This may be a little uncomfortable, but it is over quickly. In addition, during the pelvic exam your doctor will likely check for sexually transmitted diseases (STDs) like chlamydia and gonorrhea.

To confirm your pregnancy, you may have a urine pregnancy test, which checks for hCG, a hormone and pregnancy indicator. Your urine (pee) also will be tested for protein, sugar, and signs of infection.

Blood will be drawn to check for things like:

  • your blood type and Rh factor. If your blood is Rh negative and your partner's is Rh positive, you may develop antibodies that prove dangerous to your fetus. This can be prevented through a course of injections given to you.
  • anemia, a low red blood cell count
  • hepatitis B, syphilis, and HIV
  • immunity to German measles (rubella) and chickenpox (varicella)
  • cystic fibrosis — health care providers now routinely offer this screening even when there's no family history of the disorder

After the first visit, you can expect to get your urine tested and your weight and blood pressure checked at every (or almost every) visit until you deliver. The reason for this is to identify conditions such as gestational diabetes and preeclampsia.

Throughout your pregnancy, you'll be offered more tests depending on your age, health, family medical history, and other factors.

First Trimester Screen for Fetal Problems

Why Is This Screening Performed?

Doctors use this to screening test to determine a woman's risk of carrying a baby with Down syndrome (trisomy 21), Edward syndrome (trisomy 18), or other chromosomal abnormalities. It can also help determine the risk for certain birth defects like heart abnormalities.

This screening test, called the "first trimester screen," is ideally done in two parts: a blood sample (often a pinprick test to draw a drop of blood) and, usually, an ultrasound screening:

  • Blood sample (maternal blood screening). This test measures the levels of proteins in the blood. Having abnormal levels of the proteins PAPP-A (maternal serum pregnancy-associated plasma protein-A) and beta-hCG (maternal serum beta human chorionic gonadotrophin) can indicate a higher-than-average risk of carrying a baby who has chromosomal abnormalities.
  • Ultrasound screening (nuchal translucency screening). This exam measures the space in the back of the baby's neck. Extra fluid in the back of the neck (behind the neural tube) may point to a higher risk of chromosomal abnormalities. Ultrasound screenings are not offered at every medical practice.

When a woman undergoes both the blood and ultrasound screening, her doctor usually will calculate the results together. Age is also a consideration with determining these results, since women of advanced maternal age (35 and older) are at a higher risk of having children with chromosomal abnormalities. Combining the results provides a higher level of accuracy than if the screenings were calculated on their own. When screenings are calculated together, it's called a combined first trimester screening.

Not all doctors choose to calculate a woman's risk in this way. Some wait until after a woman has had other screenings in the second trimester to determine her baby's overall risk for chromosomal abnormalities. This is called an integrated screening. Other practitioners who do not offer a first trimester ultrasound determine a woman's risk using the results of her first and second trimester blood screenings. This is called a serum integrated screening.

How your doctor chooses to calculate your results depends on your age, health risks, and what services are available at the doctor's office.

Women who are shown to be at high risk for carrying a baby with Down syndrome or another chromosomal abnormality are offered diagnostic testing, usually through chorionic villus sampling (CVS) in the first trimester or amniocentesis in the second trimester. They also may be offered a new blood screening (cell-free fetal DNA testing) that evaluates the fetal DNA in a woman's blood and can give doctors an indication about certain chromosomal abnormalities.

Those who are not shown to be high risk in the first trimester are still offered a second trimester screening. That screening, which consists of more blood tests, checks for chromosomal abnormalities and neural tube defects, and helps to confirm the findings from the first trimester screen.

Should I Have This Screening?

These screenings are considered safe, but it's your decision whether or not you get them. Some people believe that screening and/or subsequent diagnostic testing can offer a bit more peace of mind during pregnancy. The benefit of getting a screening in the first trimester is more time to plan, prepare for, or address any health problems your child may have.

But remember that this is a screening, not a definitive test — it indicates whether a woman is likely to be carrying an affected fetus. To confirm a problem, further testing must be done.

When getting any screening, it's also important to remember that there's a chance of false-positives and false-negatives. False-positive results are when women whose results show high risk for a chromosomal abnormality go on to have healthy babies. False-negatives are when women whose results show low risk go on to have a baby with Down syndrome or another chromosomal abnormality.

Talk to your doctor if you have questions about these screenings or your results.

When Should I Have This Screening?

The blood screening is usually done between 9 and 14 weeks. Women who also get an ultrasound should have it done between 11 and 14 weeks.

How Is This Screening Performed?

For the blood screening, blood is obtained from the mother through a finger prick or a regular blood draw. Results are gathered in a lab. When the ultrasound is added, a woman will lie on her back while an ultrasound probe glides across her lower belly. To construct an image of the fetus, sound waves bounce off the baby's bones and tissues.

When Are the Results Available?

Blood screening results usually are ready within a week or two. Ultrasound results can be immediate.

Ultrasound

Why Is This Test Performed?

Ultrasounds were once used only in high-risk pregnancies but have become so common that they're often part of routine prenatal care.

During an ultrasound, sound waves are bounced off the baby's bones and tissues to construct an image showing the baby's shape and position in the uterus. Also called a sonogram, sonograph, echogram, or ultrasonogram, an ultrasound is done to:

  • verify the expected date of delivery
  • detect pregnancies outside the uterus
  • see whether there might be more than one fetus
  • determine whether the fetus is growing at a normal rate
  • record fetal heartbeat or breathing movements
  • check the amount of amniotic fluid in the uterus
  • indicate the position of the placenta (which block the baby's way out of the uterus) in late pregnancy
  • guide doctors during other tests, like amniocentesis
  • find structural defects that may indicate Down syndrome, spina bifida, or anencephaly
  • detect other problems such as congenital heart defects, cleft lip or palate, and gastrointestinal or kidney malformations

Should I Have This Test?

This test is considered safe. If you opt to get the first trimester screen to check for fetal health problems, an ultrasound may be offered to you. It also might be available as part of your routine prenatal care.

When Should I Have This Test?

If you're getting the first trimester screening, you'll likely get an ultrasound between 11–14 weeks. Some providers also will order an ultrasound to date the pregnancy, usually early in your first trimester.

Women with high-risk pregnancies may need to have multiple ultrasounds throughout their first trimester.

When Are Results Available?

Although the technician can see the images immediately, a full evaluation by a physician may take up to 1 week if a physician is not on site during the exam.

Depending on where you have the ultrasound done, the technician may be able to tell you that day whether everything looks OK. However, most radiology centers or health care providers prefer that technicians not comment until a specialist has taken a look — even when everything is OK.

Chorionic Villus Sampling (CVS)

Why Is This Test Performed?

Chorionic villi are tiny finger-like units in the placenta (a disk-like structure that sticks to the inner lining of the uterus and provides nutrients from the mother to the fetus through the umbilical cord). They have the same chromosomes and genetic makeup as the fetus.

During a chorionic villus sampling (CVS), some cells from the chorionic villi are removed and tested for a number of chromosomal abnormalities, like Down syndrome, Tay-Sachs disease, or Fragile X syndrome.

This screening is considered an alternative to an amniocentesis because it can be performed earlier in pregnancy, allowing more time for expectant parents to receive counseling and make decisions. Unlike amniocentesis, CVS does not provide information on neural tube defects like spina bifida. The risks of CVS are higher than with amniocentesis so the risks and benefits of the test must be weighed.

How Is This Test Performed?

This test is done in one of two ways:

  1. Transcervical: Using ultrasound as a guide, a thin tube is passed from the vagina into the cervix. Gentle suction removes a sample of tissue from the chorionic villi.
  2. Transabdominal: A needle is inserted through the abdominal wall with ultrasound guidance, and a sample of the chorionic villi is removed.

Some women find that CVS is painless. Others feel cramping, similar to period cramps, while the sample is taken. After the sample is taken, the doctor may check the fetus' heart rate. You should rest for several hours afterward.

Should I Have This Test?

Most women who are not high risk will not need this test. But your health care provider may recommend this test if you:

  • are older than age 35
  • have a family history of genetic disorders (or a partner who does)
  • have a previous child with a genetic disorder or had a previous pregnancy with a chromosomal abnormality
  • have had an earlier screening test that indicates that there may be a concern

Possible risks of this test include:

  • approximately 1% risk of miscarriage (the risk is higher with the transcervical method than with the transabdominal method)
  • infection
  • spotting or bleeding (this is more common with the transcervical method)
  • birth defects when the test is done too early in pregnancy

When Should I Have This Test?

At 10 to 12 weeks.

When Are the Results Available?

Results are usually available within a few hours to a couple of days, depending on what the test is being used to look for.

Additional Screenings for Couples at Risk

Throughout your pregnancy, your health care provider will order other tests based on, among other things, your (and your partner's) personal medical history and risk factors. If your baby is at risk for certain hereditary conditions, you will be given an appointment to speak with a genetic counselor.

Screenings or diagnostic tests offered to those at risk for certain conditions include tests for:

  • thyroid disease
  • toxoplasmosis
  • hepatitis C
  • blood disorders like sickle cell disease and alpha thalassemia or beta thalassemia
  • spinal muscular atrophy (SMA)
  • Canavan disease
  • cytomegalovirus (CMV)
  • Tay-Sachs disease
  • Fragile X syndrome
  • Tuberculosis
Reviewed by: Elana Pearl Ben-Joseph, MD
Date reviewed: January 2014

Second trimester

Throughout your pregnancy, you'll want to know how your baby is growing. You'll also want to know if how you're feeling is normal. Prenatal tests can offer you valuable information about your health and the health of your growing child.

If your doctor recommends a screening or test, be sure to learn about the risks and benefits. Most parents agree that prenatal tests offer them peace of mind while helping to prepare them for their baby's arrival. But it's your choice to accept or decline a test.

Read on to learn about tests that may be available to you during your second trimester.

Routine Screenings & Tests

Your first visit to the obstetrician (if you haven't gone already) should include a pregnancy test to confirm the pregnancy and a full physical that includes a pelvic exam. Your urine (pee) also will be tested for protein, sugar, and signs of infection.

If you're due for your routine cervical test (Pap smear), the doctor will perform it during the pelvic exam. This test detects changes in your cervical cells that could lead to cancer.

To do a Pap smear, the inside of your cervix (the opening to the uterus that's located at the very top of the vagina) will be swabbed with a cotton swab. This may be a little uncomfortable, but it is over quickly. During the pelvic exam your doctor will likely also check for sexually transmitted diseases (STDs) like chlamydia and gonorrhea.

In addition, blood will be drawn to check for things like:

  • your blood type and Rh factor. If your blood is Rh negative and your partner's is Rh positive, you may develop antibodies that prove dangerous to your fetus. This can be prevented through a course of injections given to you.
  • anemia, a low red blood cell count
  • hepatitis B, syphilis, and HIV
  • immunity to German measles (rubella) and chickenpox (varicella)
  • cystic fibrosis — health care providers now routinely offer this screening even when there's no family history of the disorder

After the first visit, you can expect to get your urine tested and your weight and blood pressure checked at every (or almost every) visit until you deliver. The reason for this is to identify conditions such as gestational diabetes and preeclampsia.

Throughout your second trimester, you'll be offered more tests depending on your age, health, family medical history, and other factors.

Multiple Marker Test

Why Is This Test Performed?

Between the 15th and 20th weeks of pregnancy, expectant mothers usually are offered a blood test called the multiple-marker test (also called the multiple marker screening, maternal serum screening, or maternal blood screening). Doctors use this test to screen for Down syndrome and neural tube defects.

Depending on the number of things measured, this screening also might be called:

  • a "triple screen" or "triple marker" because it looks at the levels of a protein, alpha-fetoprotein (AFP), and two pregnancy hormones, estriol and human chorionic gonadotropin (hCG)
  • a "quadruple screen" ("quad screen") or "quadruple marker" ("quad marker") when the level of an additional substance — inhibin-A — is also measured

This screening calculates a woman's individual risk based on the levels of the three (or more) substances, as well as:

  • her age
  • her weight
  • her race
  • whether she has diabetes requiring insulin treatment
  • whether she is carrying one fetus or multiple ones

The greater number of markers increases the accuracy of the multiple marker test and better identifies the possibility of a problem. In some cases, doctors will combine the results of this test with results from the first trimester screen (a blood test and/or ultrasound done at around 13 weeks to check for chromosomal abnormalities) to get an even better idea of a baby's risk for Down syndrome and neural tube defects.

Should I Have This Test?

All women are offered some form of this test. Some practitioners include more parts of it than others. Remember that this is a screening, not a definitive test — it indicates whether a woman is likely to be carrying an affected fetus. It's also not foolproof — Down syndrome, another chromosomal abnormality, or a neural tube defect may go undetected, and some women with abnormal levels have been found to be carrying a healthy baby. Further testing is recommended to confirm a positive result.

When Should I Have This Test?

The blood tests are typically done between 15 and 20 weeks.

How Is the Test Performed?

Blood is drawn from the mother.

When Are the Results Available?

Usually within a week, although it may take up 2 weeks.

Ultrasound

Why Is This Test Performed?

Ultrasounds were once used only in high-risk pregnancies but have become so common that they're often part of routine prenatal care.

During an ultrasound, sound waves are bounced off the baby's bones and tissues to construct an image showing the baby's shape and position in the uterus. Also called a sonogram, sonograph, echogram, or ultrasonogram, ultrasounds are used to:

  • verify the expected date of delivery
  • detect pregnancies outside the uterus
  • see whether there might be more than one fetus
  • determine whether the fetus is growing at a normal rate
  • record fetal heartbeat or breathing movements
  • check the amount of amniotic fluid in the uterus
  • indicate the position of the placenta in late pregnancy (which can sometimes block the baby's way out of the uterus)
  • guide doctors during other tests, like amniocentesis
  • find structural defects that may indicate Down syndrome, spina bifida, or anencephaly
  • detect other problems such as congenital heart defects, cleft lip or palate, and gastrointestinal or kidney malformations

Should I Have This Test?

This test is considered safe, but it's up to you to decide whether to undergo it. Talk to your health care provider to find out why this test is recommended for you.

When Should I Have This Test?

Ask your doctor when you will need to have an ultrasound. Most second-trimester ultrasounds, or "level 2" ultrasounds, are usually given between 18 and 20 weeks to examine a baby's anatomy and to confirm that the baby is developing normally.

It's during this test that a baby's gender usually can be determined (as long as the baby is "cooperating" and in the right position). If you want your baby's gender to be a surprise, make sure to tell the doctor or technician at the start of your test.

Women with high-risk pregnancies may need to have multiple ultrasounds throughout their second trimester.

When Are Results Available?

Although the technician can see the images immediately, a full evaluation by a doctor may take up to 1 week if one is not on site during the exam.

Depending on where you have the ultrasound done, the technician may be able to tell you that day whether everything looks OK. However, most radiology centers or health care providers prefer that technicians not comment until a specialist has taken a look — even when everything is OK.

Glucose Screening

Why Is This Test Performed?

Glucose screenings check for gestational diabetes, a short-term form of diabetes that develops in some women during pregnancy. Gestational diabetes is increasing in frequency in the United States, and may occur in 3% to 8% of pregnancies. Gestational diabetes can cause health problems for the baby, especially if it is not diagnosed or treated.

Should I Have This Test?

Most women have this test, and if they have gestational diabetes, are treated to reduce the risk to the baby.

When Should I Have This Test?

Screening for gestational diabetes usually is done at 24 to 28 weeks. Testing may be done earlier for women who are at higher risk of having it, such as those who:

  • have previously had a baby that weighed more than 9 pounds (4.1 kilograms)
  • have a family history of diabetes
  • are obese
  • are older than age 25
  • have sugar in the urine on routine testing
  • have high blood pressure (hypertension)
  • have polycystic ovary syndrome (POS)

How Is the Test Performed?

This test involves drinking a sugary liquid and then having your blood drawn after an hour. If the sugar level in the blood is high, you'll have a glucose-tolerance test, which means you'll drink a glucose solution on an empty stomach and have your blood drawn once every hour for 3 hours.

When Are the Results Available?

The results are usually available within 1 to 2 days. Ask if your health care provider will call you with the results if they are normal or only if the reading is high and you need to come in for another test.

Amniocentesis

Why Is This Test Performed?

This test takes a sample of the amniotic fluid that surrounds your baby, and examines the substances in the fluid, like genetic information. It is most often used to identify:

  • Down syndrome and other chromosome abnormalities
  • structural defects such as spina bifida and anencephaly
  • inherited metabolic disorders like PKU (phenylketonuria)

Doctors sometimes check for infection and Rh incompatibility with this test. Late in the pregnancy, this test can reveal if a baby's lungs are strong enough to allow the baby to breathe normally after birth. This can help the health care provider make decisions about inducing labor or trying to prevent labor, depending on the situation. For instance, if a mother's water breaks early, the health care provider may want to try to hold off on delivering the baby as long as possible to allow the baby's lungs to mature.

Other common birth defects, such as heart disorders and cleft lip and palate, can't be determined using this test.

Should I Have This Test?

Your health care provider may recommend this test if you:

  • had an abnormal screening test
  • are older than age 35
  • have a family history of genetic disorders (or a partner who does)
  • have had a previous child with a birth defect or had a previous pregnancy with a chromosomal abnormality or neural tube defect

This test can be very accurate — close to 100% — but only certain disorders can be detected. The rate of miscarriage with this procedure is between 1 in 300 and 1 in 500. It also carries a low risk of uterine infection, which can also cause miscarriage, leakage of amniotic fluid, and injury to the fetus.

Talk to your doctor to find out why this test is recommended for you, and to weigh the pros and cons of undergoing this test.

When Should I Have This Test?

Amniocentesis is usually performed between 15 and 20 weeks.

How Is the Test Performed?

While watching with an ultrasound, the doctor inserts a needle through the abdominal wall into the uterus to remove some (about 1 ounce) of the amniotic fluid. Some women report that they experience cramping when the needle enters the uterus or pressure while the doctor retrieves the sample.

The doctor may check the fetus' heartbeat after the procedure to make sure it's normal. Most doctors recommend rest for several hours afterward.

The cells in the withdrawn fluid are grown in a special culture and then analyzed (the specific tests conducted on the fluid depend on personal and family medical history).

When Are the Results Available?

Timing varies; depending on what is being tested for, the results are usually available within 1 to 2 weeks. Tests of lung maturity are often available within a few hours.

Percutaneous Umbilical Blood Sampling (PUBS)

Why Is This Test Performed?

This test obtains fetal blood by guiding a needle into the umbilical cord. It is primarily used in addition to an ultrasound and amniocentesis if your health care provider needs to quickly check your baby's chromosomes for defects or disorders or is concerned that your baby may have another problem, such as a low platelet count or a thyroid condition. Alternative names for PUBS include cordocentesis, fetal blood sampling, or umbilical vein sampling.

The advantage to this test is its speed. In some situations (such as when a fetus shows signs of distress) it's helpful to know whether the fetus has a fatal chromosomal defect. If the fetus is suspected to be anemic or to have a platelet disorder, this test is the only way to confirm it because it uses a blood sample rather than an amniotic fluid sample. It also allows transfusion of blood or needed fluids into the baby while the needle is in place.

Should I Have This Test?

This test may be used:

  • after an abnormality has been noted on an ultrasound
  • when results from other tests, such as amniocentesis or CVS, aren't conclusive
  • if the fetus may have Rh incompatibility, to determine whether the baby has an infection if you've been exposed to an infectious disease

Risks are associated with this procedure, such as miscarriage or infection. The risks and benefits should be discussed with your health care provider if you choose to have this test.

When Should I Have This Test?

After 18 weeks.

How Is the Test Performed?

A fine needle is passed through your abdomen and uterus into the umbilical cord and blood is withdrawn for testing.

When Are the Results Available?

Usually within 3 days.

More Screenings for Couples at Risk

Throughout your pregnancy, your health care provider will order other tests based on, among other things, your (and your partner's) personal medical history and risk factors. If your baby is at risk for certain hereditary conditions, you will be given an appointment to speak with a genetic counselor.

Screenings or diagnostic tests offered to those at risk for certain conditions include tests for:

  • thyroid disease
  • toxoplasmosis
  • hepatitis C
  • blood disorders like sickle cell disease and alpha thalassemia or beta thalassemia
  • spinal muscular atrophy (SMA)
  • Canavan disease
  • cytomegalovirus (CMV)
  • Tay-Sachs disease
  • Fragile X syndrome
  • tuberculosis
Reviewed by: Elana Pearl Ben-Joseph, MD
Date reviewed: January 2014

Third trimester

Third trimester tests can offer you valuable information about your health and the health of your growing child. If your doctor recommends a screening or test, be sure to learn about the risks and benefits. Most parents agree that prenatal tests offer them peace of mind while helping to prepare them for their baby's arrival. But it's your choice to accept or decline a test.

Read on to learn about tests that may be available to you during your third trimester.

OB Visit Screenings & Tests

Your first visit to the obstetrician should have included a full physical, urine test, and blood test to check for things like:

  • your blood type and Rh factor. If your blood is Rh negative and your partner's is Rh positive, you may develop antibodies that prove dangerous to your fetus. This can be prevented through a course of injections given to you.
  • anemia, a low red blood cell count
  • hepatitis B, syphilis, and HIV
  • immunity to German measles (rubella) and chickenpox (varicella)
  • cystic fibrosis — health care providers now routinely offer this screening even when there's no family history of the disorder

After the first visit, you can expect to get your urine tested and your weight and blood pressure checked at every (or almost every) visit until you deliver. The reason for this is to identify conditions such as gestational diabetes and preeclampsia.

Between your 35th and 37th weeks of pregnancy, the doctor will check you for group B streptococcus (GBS) infection. GBS bacteria are found naturally in the vaginas of many women but can cause serious infections in newborns. This test involves swabbing the vagina and rectum. A woman whose test comes back positive must go to the hospital as soon as labor begins so that intravenous (IV) antibiotics can be started to reduce the chance of the baby being infected with this illness.

Throughout your third trimester, you'll be offered more tests depending on your age, health, family medical history, and other factors.

Glucose Screening

Why Is This Test Performed?

Glucose screening checks for gestational diabetes, a short-term form of diabetes that develops in some women during pregnancy. Gestational diabetes can cause health problems for the baby, especially if it is not diagnosed or treated.

Should I Have This Test?

Most women have this test, and if they have gestational diabetes, are treated to reduce the risk to the baby.

When Should I Have This Test?

Screening for gestational diabetes usually is done at 24 to 28 weeks. Testing may be done earlier for women who are at higher risk for it, such as those who:

  • have previously had a baby that weighed more than 9 pounds (4.1 kilograms)
  • have a family history of diabetes
  • are obese
  • are older than age 25
  • have sugar in the urine on routine testing
  • have high blood pressure
  • have polycystic ovary syndrome (POS)

How Is the Test Performed?

This test involves drinking a sugary liquid and then having your blood drawn after an hour. If the sugar level in the blood is high, you'll have a glucose-tolerance test, which means you'll drink a glucose solution on an empty stomach and have your blood drawn once every hour for 3 hours.

When Are the Results Available?

The results are usually available within 1 to 2 days. Ask if your health care provider will call you with the results if they are normal or only if the reading is high and you need to come in for another test.

Nonstress Test

Why Is This Test Performed?

A nonstress test (NST) can determine if the baby is responding normally to a stimulus. It is used mostly in high-risk pregnancies or when a health care provider is uncertain of a baby's movements, and usually can be performed after 26 weeks. This is when a baby's heart rate can appropriately respond by speeding up or slowing down.

This test may also be done if you've gone beyond your due date. The NST can help a doctor make sure that the baby is receiving enough oxygen and is responding to stimulation. However, an unresponsive baby isn't necessarily in danger, though further testing might be needed.

Sometimes, a biophysical profile (BPP) is done, which includes an ultrasound and an NST. A BPP examines a baby's breathing, movement, amount of amniotic fluid, and tone, in addition to the heart rate response.

Should I Have This Test?

Your health care provider may recommend this if you have a high-risk pregnancy, if there are concerns during your pregnancy, or if you have a low-risk pregnancy but are past your due date.

When Should I Have This Test?

An NST may be recommended any time after 26 to 28 weeks, depending on why it is needed.

How Is the Test Performed?

The health care provider will measure the response of the fetus' heart rate to each movement the fetus makes as reported by the mother or observed by the doctor on an ultrasound screen. If the fetus doesn't move during the test, he or she may be asleep and the health care provider may use a buzzer to wake the baby. You also may be asked to drink or eat to try to stimulate the baby more.

When Are the Results Available?

Immediately.

Ultrasound

Why Is This Test Performed?

Ultrasounds were once used only in high-risk pregnancies but have become so common that they're often part of routine prenatal care.

During an ultrasound, sound waves are bounced off the baby's bones and tissues to construct an image showing the baby's shape and position in the uterus. Also called a sonogram, sonograph, echogram, or ultrasonogram, ultrasounds are used to:

  • verify the expected date of delivery
  • detect pregnancies outside the uterus
  • see whether there might be more than one fetus
  • determine whether the fetus is growing at a normal rate
  • record fetal heartbeat or breathing movements
  • check the amount of amniotic fluid in the uterus
  • indicate the position of the placenta in late pregnancy (which can sometimes block the baby's way out of the uterus)
  • guide doctors during other tests, like amniocentesis
  • find structural defects that may indicate Down syndrome, spina bifida, or anencephaly
  • detect other problems such as congenital heart defects, cleft lip or palate, and gastrointestinal or kidney malformations

Should I Have This Test?

This test is considered safe, but it's up to you to decide whether you want to undergo it. Talk to your health care provider to find out why this test is recommended for you.

When Should I Have This Test?

Ask your doctor when you will need to have an ultrasound. Women with high-risk pregnancies may need to have multiple ultrasounds throughout their third trimester to make sure a baby is developing normally.

Sometimes, when a doctor is uncertain of a baby's movements, a biophysical profile (BPP) is done, which can include an ultrasound and a nonstress test (NST). A BPP examines a baby's breathing, movement, amount of amniotic fluid, and tone, in addition to the heart rate response.

When are results available?

Although the technician can see the images immediately, a full evaluation by a doctor may take up to 1 week if one is not on site during the exam.

Depending on where you have the ultrasound done, the technician may be able to tell you that day whether everything looks OK. However, most radiology centers or health care providers prefer that technicians not comment until a specialist has taken a look — even when everything is OK.

Contraction Stress Test

Why Is This Test Performed?

This test stimulates the uterus with pitocin, a synthetic form of oxytocin (a hormone secreted during childbirth), to determine the effect of contractions on fetal heart rate. It may be recommended when a nonstress test or biophysical profile indicates a problem and can determine whether the baby's heart rate remains stable during contractions.

Should I Have This Test?

This test may be ordered if the nonstress test or biophysical profile indicates a problem. However, it can induce labor.

When Should I Have This Test?

Your doctor may schedule it if he or she is concerned about how the baby will respond to contractions or feels that it is the appropriate test to determine the fetal heart rate response to a stimulus.

How Is the Test Performed?

Mild contractions are brought on either by injections of pitocin or by squeezing the mother's nipples (which causes oxytocin to be secreted). The fetus' heart rate is then monitored.

When Are the Results Available?

Immediately.

Reviewed by: Elana Pearl Ben-Joseph, MD
Date reviewed: January 2014

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