Prenatal Tests: Second Trimester

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

If your doctor recommends a test, ask about the 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.

Routine Screenings & Other 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 include it as part of the pelvic exam. This test detects changes in your 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.

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.

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 conditions such as gestational diabetes and preeclampsia (dangerously high blood pressure).

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

• Multiple marker test: This blood test is done between weeks 15 and 20 to screen for neural tube defects (such as spina bifida) and chromosomal disorders (such as Down syndrome and trisomy 18). Test results can be combined with first trimester screening tests to give more accurate results (this is called an integrated screening test).
• Ultrasound: An ultrasound is a safe and painless test that uses sound waves to make images that show the baby's shape and position in the uterus. Most second-trimester ultrasounds, or "level 2" ultrasounds, are done between 18–20 weeks to examine the baby's anatomy and confirm that the baby is developing normally. Women with high-risk pregnancies may have multiple ultrasounds in their second trimester.
• Glucose screening: This test checks for gestational diabetes, a short-term form of diabetes that develops in some women during pregnancy and can cause health problems for the baby, especially if it is not diagnosed or treated. You'll drink a sugary liquid, then have a blood test an hour later to check glucose levels. It's usually done at 24 to 28 weeks, but can be earlier if a woman is at higher risk for gestational diabetes.
• Amniocentesis: This test takes a sample of the amniotic fluid that surrounds a baby to check for signs of problems such as chromosomal disorders, genetic problems, and neural tube defects. It's usually done between 15 and 20 weeks in women who are considered at higher risk of having a baby with these disorders.
• Percutaneous umbilical blood sampling (PUBS): Also known as cordocentesis, fetal blood sampling, or umbilical vein sampling, this quick test examines fetal blood directly from the umbilical cord to detect disorders in the fetus. It's usually done after 18 weeks of pregnancy. It's not done as often as other diagnostic tests (such as amniocentesis and chorionic villus sampling), but may be used if results from those tests are not conclusive.

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

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.