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Pregnancy tests by the trimester: Everything you need to know about screenings
Routine screening tests during pregnancy can help make sure you stay safe and healthy. Here are the most common ones you’ll likely need.
Now that you’re pregnant, your doctor or midwife is going to want to keep track of how you’re doing. And routine screenings help them do exactly that.
Some tests check to see if your baby is at a higher risk of certain chronic diseases or genetic mutations, says ob-gyn Meagan Haynes, M.D. Other tests look for underlying health conditions that can lead to preterm labor. Your provider will also check for infections, she says.
The good news: All these tests will help keep you and your fetus as safe as possible during your pregnancy. And many conditions can be safely treated if they are caught early, according to the American College of Obstetricians and Gynecologists (ACOG).
Here are some common screening tests most women receive throughout pregnancy.
First trimester screening tests
Sexually transmitted infection (STI) tests
What it is: Your provider will draw your blood to test it for syphilis, HIV, hepatitis C, and hepatitis B. They will also take a swab from your cervix to test for chlamydia and gonorrhea.
When it’s done: Your first prenatal visit.
Why it’s done: Some STIs can cause pregnancy complications. Others can cause problems for your baby after birth. “Certain infections, like chlamydia, are easily treated,” Dr. Haynes says. “But if they aren’t detected, they can cause significant problems for the mother in the future.”
This includes pelvic pain and infertility in the parent, or vision problems in the baby, Dr. Haynes says. Other STIs, like HIV, are treated with antiviral medicine. With the right treatment, the chances of passing the virus to your baby are very low.
Urine test
What it is: A sample of your urine. It gets sent to a lab to look for signs of infections and other complications.
When it’s done: At each prenatal visit.
Why it’s done: “Urine samples help screen for certain diseases, like gestational diabetes, preeclampsia, and urinary tract infections,” Dr. Haynes says.
Rh-factor blood test
What it is: A blood test that detects whether your blood has Rh factor, a protein that’s found on red blood cells.
When it’s done: Your first prenatal visit. If you are Rh-negative, another test will be done between weeks 28 and 29.
Why it’s done: Most people have Rh factor, meaning they’re Rh-positive. But if you’re Rh-negative and your baby is Rh-positive, that is a concern. Your body can create antibodies that may damage your baby’s red blood cells, according to ACOG. This typically does not cause problems for a first pregnancy. But the antibodies can cause issues in later pregnancies.
Nuchal translucency screening
What it is: An ultrasound that measures the thickness of the space at the back of the baby's neck. (Ultrasound gives your doctor a view of your fetus inside the womb.)
When it’s done: Between 11 and 14 weeks.
Why it’s done: This screening is coupled with your age and your blood levels of PAPP-A (a protein) and HCG (a hormone). It helps doctors figure out your baby’s risk of certain chromosomal conditions, including Down syndrome, according to the Mayo Clinic.
Blood tests for various genetic disorders
What it is: Tests that give parents information on whether their baby might be at risk for certain genetic disorders. These are caused by changes in a person’s genes or chromosomes, according to ACOG.
When it’s done: Depending on the test, during the first or second trimester.
Why it’s done: To find out your baby’s risk for conditions such as cystic fibrosis, Tay-Sachs, sickle cell disease, Down syndrome, and neural tube defects, among others. Genetic screening tests are optional. It’s your choice whether to have them, says ACOG. Talk to your provider if you’re unsure.
Second trimester screening tests
Ultrasound
What it is: A standard ultrasound to check your baby’s health and development.
When it’s done: Between 18 and 22 weeks.
Why it’s done: It allows your doctor to see how your baby is developing and if there are any health conditions. This ultrasound also provides information about size and weight, position in the womb, and more. You will get a peek too. Your doctor might also be able to tell whether you’re having a boy or girl.
Glucose tolerance test
What it is: This is a measurement of your blood sugar levels. You’ll drink a glucose-containing liquid, then have your blood drawn. If the results indicate your blood sugar levels are high, you’ll likely have a follow-up test.
When it’s done: Between 24 and 28 weeks. (If you had gestational diabetes during a previous pregnancy, this test may be done earlier, according to the March of Dimes.)
Why it’s done: The test looks for gestational diabetes, a type of high blood sugar that’s first diagnosed during pregnancy. If the test shows you have gestational diabetes, your doctor will help you lower your blood sugar levels with diet changes, lifestyle tweaks, or medication. They may also perform nonstress tests, which track your baby’s heart rate.
Third trimester screening tests
Group B strep
What it is: A swab of your vagina and rectum that is tested for the presence of group B streptococcus (GBS). This is a type of bacteria commonly found in the gastrointestinal and genital tracts.
When it’s done: This is usually done between 36 and 38 weeks.
Why it’s done: GBS isn’t usually harmful. But if you currently have the bacteria in your body, there’s a small chance you could pass it on to your baby during birth. If that happens, your baby could develop an infection like pneumonia. If you test positive for GBS, your doctors will give you an antibiotic during labor to help protect your baby.
Additional sources:
Screening tests background: American College of Obstetricians and Gynecologists
Genetic screening tests: American College of Obstetricians and Gynecologists
Nuchal translucency test: Mayo Clinic
Gestational diabetes: March of Dimes
Blue Cross and Blue Shield of Kansas City is an independent licensee of the Blue Cross and Blue Shield Association.
