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The complete guide to second trimester pregnancy tests

With phase two of your journey to motherhood underway, it's safe to assume you've already had a number of medical tests at your earlier prenatal care appointments. Soon you'll probably have more. 

Some of these tests—like blood pressure checks—are first trimester repeats. Others may be offered for the first time. Remember, mom-to-be, prenatal tests can help spot conditions, like birth defects, or pregnancy problems that may need treatment to help keep you and baby healthy. 

Two main kinds of tests

Prenatal tests can be done for either screening or diagnostic purposes. What's the difference?

  • Screening tests look for a higher risk of a health problem. But they can't show whether a problem actually exists. With screening tests, there's no chance of harm to you or your baby.
  • Diagnostic tests are the only tests that can say for sure if your baby has a condition, like a birth defect. Your provider may recommend one after a screening test. Unlike screenings, some diagnostic tests may have risks—for instance, a small chance of miscarriage. And they're totally optional. Some parents may not want to know if their baby has a birth defect. Others may find the knowledge helps them prepare for baby's arrival. 

A tour of second trimester tests 

Some prenatal tests are routine. Your provider may suggest other tests if your baby's risk for certain conditions is higher because of your age, family history, ethnic background or previous test results. 

You and your provider can discuss what's right for you, but here are some second trimester tests that they may suggest:

Maternal blood screening. This screening checks your baby's blood for substances that may suggest a higher risk of birth defects, including Down syndrome. It's usually done at around 15 to 22 weeks of pregnancy.

Amniocentesis. This diagnostic test is usually done at 14 to 20 weeks. A needle removes a sample of amniotic fluid and cells from around your baby. The sample is checked for problems such as Down syndrome, cystic fibrosis or spina bifida. 

Ultrasound exam. With this test, sound waves are used to see your baby inside your womb. While you may have had an ultrasound before, you may need one again to gauge your baby's growth and to look for some birth defects.

Glucose screening. You'll likely have this test at 24 to 28 weeks. It checks your blood sugar level to show whether you have gestational diabetes. That's a type of diabetes that some women get when they're pregnant. 

More pregnancy news

Learn more about what you can expect during your second trimester.

Sources: American College of Obstetricians and Gynecologists; March of Dimes; Office on Women's Health

Reviewed 1/20/2023

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