Prenatal Testing: First Trimester

Overview

What Is Prenatal Testing?

Prenatal tests are tests that happen during pregnancy to check your health and your baby’s health. (“Prenatal” means before birth.)

Some prenatal tests are screening tests that can only show the chance of a problem. Other prenatal tests are diagnostic tests that can find out if your baby has a certain problem. Sometimes you’ll have a screening test first, then a diagnostic test.

While you’re pregnant, prenatal lab work — like blood tests — is offered during the first trimester (weeks 1–12), second trimester (weeks 13–27), and third trimester (weeks 28–40).

Top Things to Know

• First trimester tests are early tests that can show how your pregnancy is going.
• Blood tests can tell if you have health problems, like certain infections, that might harm your baby.
• An ultrasound test shows pictures of how your baby is growing.
• If your baby might have a genetic condition, a genetic counselor will talk with you about it.

Do I Need to Have Prenatal Tests?

If your doctor wants you to have a test, ask about the risks and benefits. For most parents, prenatal tests put their minds at ease while helping them get ready for their baby to arrive. But it's your choice whether to have a test or not have it.

What Can I Expect at My First Prenatal Visit?

At your first prenatal visit, the doctor or nurse practitioner will check that you’re pregnant and see if you or your baby might have any health problems later on.

You may have a urine (pee) pregnancy test, which looks for a hormone called human chorionic gonadotropin (hCG). Levels go up when you’re pregnant. Your pee will also be tested for protein, sugar, and infections.

Once it’s confirmed that you’re pregnant, your doctor will tell you your due date (when your baby might be born). This is based on when you had your last period. Sometimes a prenatal ultrasound (a test that uses sound waves to make a picture of your baby) can help figure out the due date.

The doctor will do a full physical exam, which may include checks of your weight and blood pressure, a breast exam, and a pelvic exam. If you're due for a cervical test (Pap smear), the doctor may do it during the pelvic exam. A Pap smear looks for changes in cells in your cervix (where the vagina and uterus join) that could lead to cancer. During the pelvic exam, your doctor will also check for sexually transmitted diseases or STDs like chlamydia (kluh-MID-ee-uh) and gonorrhea (gah-nuh-REE-uh).

What About Blood Tests?

At your first prenatal visit your doctor may suggest you have prenatal blood tests that check for things like:

• Your blood type and Rh factor (a kind of protein). If you don’t have Rh factor in your blood and your baby does, your body may think your baby’s blood is dangerous and make proteins called antibodies that attack it. This can be harmful to the baby, but having a shot around the 28th week of pregnancy will help keep your child safe.
• Anemia, a low level of red blood cells.
• Hepatitis B, hepatitis C, syphilis, and HIV.
• Protection against rubella (German measles) and chickenpox. You may have immunity or be protected if you’ve gotten vaccines for these infections in the past.
• Cystic fibrosis and spinal muscular atrophy. These conditions are often inherited (passed from parents to children through genes). But doctors can check for them even if no one in your family has had them.

What Other Tests Are Done in the First Trimester?

After the first visit, your pee, weight, and blood pressure will be checked at each visit, or almost every visit, until you give birth. These checks can find problems like gestational diabetes and if there’s a risk for preeclampsia (high blood pressure that develops in the second half of pregnancy or soon after the baby is born). You might need other tests to confirm that you have certain conditions.

During your first trimester — depending on your age, health, family medical history, and other things — you'll be offered more tests, such as:

• First trimester screening: This includes a blood test and an ultrasound. The screening helps look for any problems your baby may have with chromosomes (tiny strands inside cells that carry genes), like Down syndrome, or birth defects, like heart problems.
• Ultrasound: This test shows your baby's shape and position. It can be done early in the first trimester to help figure out the due date or during weeks 11–14. If you have a “high-risk” pregnancy, you might have more ultrasounds during your first trimester.
• Chorionic villus sampling (CVS): This test checks cells from the placenta (the tissue that brings nutrients and oxygen to the baby) to see if there’s a chromosome problem. The test can be done from weeks 10–13, but sometimes it’s done later in pregnancy.
• Cell-free DNA testing/noninvasive prenatal screening (NIPS): This blood test checks for your baby’s DNA in your blood to see if your baby might have certain chromosome problems. You can have the test in week 10 or later. Based on the results, you might need another test. NIPS tends to be offered in high-risk pregnancies because they have a greater chance for chromosome problems.

Will My Doctor Recommend More Tests?

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

Your doctor may suggest testing for:

• infections such as:
  • tuberculosis (TB)
  • cytomegalovirus (CMV)
  • toxoplasmosis (tok-so-plaz-MOE-sis)
• inherited conditions such as:
  • Tay-Sachs disease
  • fragile X syndrome
  • Canavan disease (a rare disorder of the nervous system)

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.

Tests are offered to you, so it's your choice if you want to have them 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.