What Are Prenatal Tests?

Prenatal tests are tests done during pregnancy to check a woman's health and her baby's. They can detect conditions that can put a baby at risk for problems like preterm birth if they're not treated. Tests also can help health care providers find things like a birth defect or a chromosomal abnormality.

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.

If your doctor recommends a test, ask about its risks and benefits. Most parents find 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.

What Tests Are Done at the Prenatal First Visit?

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

The doctor will do a full physical exam, 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 do it during the pelvic exam. This test detects changes in cervical cells that could lead to cancer. During the pelvic exam, your doctor also will 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 is tested for protein, sugar, and signs of infection. When your pregnancy is confirmed, your due date is calculated based on the date of your last menstrual cycle (period). Sometimes an ultrasound exam will help to figure this out.

A blood test will 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 an injection given around the 28th week of pregnancy.
• anemia, a low red blood cell count
• hepatitis B, syphilis, and HIV
• immunity to German measles (rubella) and chickenpox (varicella)
• cystic fibrosis and spinal muscular atrophy. Health care providers now routinely offer to screen for these disorders even when there's no family history.

What Other Tests Are Done in the First Trimester?

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. These tests can find problems such as gestational diabetes and preeclampsia (dangerously high blood pressure).

During your first trimester, you'll be offered more tests depending on your age, health, family medical history, and other things. These can include:

• First trimester screening: This test includes a blood test and an ultrasound exam. It helps to determine whether the fetus is at risk for a chromosomal abnormality (such as Down syndrome) or birth defects (such as heart problems).
• Ultrasound: This safe and painless test uses sound waves to make images that show the baby's shape and position. It can be done early in the first trimester to date the pregnancy or during weeks 11–14 as part of the first trimester screening. Women with high-risk pregnancies might have multiple ultrasounds during their first trimester.
• Chorionic villus sampling (CVS): This test checks cells from the placenta to see if they have a chromosomal abnormality (such as Down syndrome). It can be done from weeks 10 to 13, and can tell for sure if a baby will be born with a specific chromosomal disorder.
• Cell-free DNA testing/Non-invasive prenatal screening (NIPS): This blood test checks for fetal DNA in the mother's blood. It's done to see whether the fetus is at risk for a chromosomal disorder, and can be done from 10 weeks on. It is not a diagnostic test. If the results are abnormal, another test must confirm or rule out the diagnosis. It's usually offered to pregnant women at higher risk because they're older or have had a baby with a chromosomal abnormality.

What Other Tests Might Be Offered?

Health care providers might order other tests during a woman's pregnancy based on such things as her (and her partner's) personal medical history and risk factors. It's important to speak with a genetic counselor if your baby is at risk for hereditary conditions.

Screening or diagnostic tests offered include tests for:

• thyroid disease
• toxoplasmosis
• hepatitis C
• cytomegalovirus (CMV)
• Tay-Sachs disease
• fragile X syndrome
• tuberculosis
• Canavan disease (a rare neurological disorder)

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.