Prenatal Testing: Second Trimester

Overview

Prenatal Testing in the Second Trimester

Throughout your pregnancy, you'll want to know how your baby is growing. Prenatal tests in the second trimester (weeks 13–27) can offer helpful information about your health and your baby’s health.

Some prenatal tests in the second trimester are screening tests that show only the chance of a problem. Other prenatal tests are diagnostic tests that find out if your baby has a certain problem. Sometimes you’ll have a screening test first, then a diagnostic test. Certain diagnostic tests may done by a doctor called a maternal-fetal medicine (MFM) specialist.

Top Things to Know

• Second trimester tests check how your pregnancy is going.
• Your doctor will test your urine (pee), weight, and blood pressure at each visit.
• Blood tests can screen for certain problems with genes.
• A glucose screening looks for gestational diabetes (short-term diabetes during pregnancy).

Do I Need to Have Prenatal Tests?

If your doctor recommends a prenatal test, ask about the risks and benefits. Most parents find that the tests put their minds at ease while helping prepare them for their baby's arrival. But it's your choice to have a test or not have it.

What Tests Can I Expect at Second Trimester Visits?

In the second trimester, you can expect to have lab tests (like pee and blood tests) and checks of your weight and blood pressure at each visit, or almost every visit, until you give birth. The results can show if there are problems like gestational diabetes or a risk for preeclampsia (high blood pressure that develops in the second half of pregnancy, or soon after a baby is born). You might need other tests to confirm that you have certain conditions.

Will My Doctor Offer Other Prenatal Tests?

Your doctor might want you to have other tests (like blood tests) during the second trimester of pregnancy. These might be based on your age, health, your and your partner's medical history, and risk factors (things that increase the chance of having a condition).

You’ll be offered tests such as:

• Cell-free DNA testing/non-invasive prenatal screening (NIPS): This blood test for certain genetic problems may be offered if you didn’t have it in the first trimester (weeks 1–12).
• Quad screen (also called a multiple marker test): This blood test is done between weeks 15 and 22, but the best time is weeks 16–18. A quad screen looks for problems with chromosomes (tiny parts of cells that carry genes), like Down syndrome and trisomy 18. Your doctor may combine the test findings with ones from first trimester screening tests for more precise results — this is called an integrated screening test.
• Maternal serum alpha-fetoprotein (MSAFP): This test looks for neural tube defects (birth defects of the brain and spinal cord), like spina bifida. It’s offered in weeks 15–20.
• Ultrasound: This test uses sound waves to make pictures that show the baby's shape and position in the uterus (womb). Most second-trimester ultrasounds, or “level 2” ultrasounds, are done between 18–22 weeks to see if the baby is developing normally. If you have a “high-risk” pregnancy, you might have more ultrasounds in your second trimester.
• Glucose screening: This test checks for gestational diabetes, a short-term form of diabetes that may happen during pregnancy and can cause health problems for the baby, mainly if it’s not treated. You'll drink a sugary liquid, then have a blood test an hour later to check your glucose levels. The test is usually done at 24–28 weeks, but it can be earlier if you have a higher chance of having gestational diabetes.
• Amniocentesis: This test takes a sample of the amniotic fluid that the baby floats in to check for signs of things like chromosome problems, genetic conditions, and structural defects (problems with how the body is forming). The test is usually offered after week 15 of pregnancy.
• Percutaneous umbilical blood sampling (PUBS): This test looks at blood from the umbilical cord to see if the baby has certain conditions. It's usually done after 17 weeks of pregnancy.  Doctors tend to recommend a PUBS test if the baby has anemia (a low number of red blood cells).

What Else Should I Know?

Earlier in pregnancy, you may have been offered several tests in the first trimester (weeks 1–12). If not, you can have some of those tests in the second trimester. 

If genetic tests show that your baby might have an inherited condition, it's important to talk with a genetic counselor. Your doctor can suggest one.

It's your choice if you want to have the tests or not. To decide which ones are right for you, talk with your doctor. Ask why a test is recommended, what its risks and benefits are, and what the results can — and can't — tell you.