Prenatal tests

Prenatal tests are important ways your doctor can check on your health and well-being and that of your growing baby. Here we explain which tests you should have and what to expect.

First trimester tests (weeks 1-12)

At your first prenatal visit:

Your doctor will give you a thorough physical, including a pelvic exam.
You’ll have a Pap smear (unless you’ve had one recently) to check for abnormal cervical cells.
You may also have a culture taken to check for chlamydia and gonorrhea.
You’ll have an ultrasound to predict the baby’s due date.
Your doctor will order routine blood tests to identify your blood type and Rh status, and if you have anemia. The lab will also test your blood for:
- Syphilis
- Hepatitis B
- Immunity to German measles (rubella)
- Immunity to chicken pox
- Immunity to Parvovirus and toxoplasmosis
- HIV (the virus that causes AIDS). If you test positive for HIV, being treated during pregnancy can dramatically reduce your chances of passing on the infection to your baby.
You’ll be asked for a urine sample to test for urinary tract infections and other conditions.
If you’re at very high risk for gestational diabetes, you will probably be given a 1-hour blood glucose challenge test (GCT). If you “fail” this test, you will be given a 3-hour blood glucose tolerance test (GTT) as soon as possible.
Your thyroid function will be tested.
In some cases, you may have a skin test performed to see if you’ve been exposed to tuberculosis.
The cell-free fetal DNA test is done as early as 10 weeks and specifically tests for chromosomes 21, 18, 13 and the sex chromosomes. It can detect Down syndrome and a few other conditions.
Depending on your ethnic background and medical history, your doctor may recommend that you undergo carrier screening to determine whether your baby is at risk for genetic disorders such as cystic fibrosis, fragile x, spinal muscular atrophy (SMA), sickle cell disease, thalassemia and Tay-Sachs disease.
Finally, you may choose to have chorionic villus sampling (CVS), an invasive genetic diagnostic test that’s generally done at about 10-12 weeks. CVS can detect whether your baby has Down syndrome or other chromosomal abnormalities, and will test for certain genetic disorders your baby may be at risk for.

Second trimester tests (weeks 13-27)

During your second trimester prenatal visits:

You’ll be asked for a urine sample to screen for signs of preeclampsia, urinary tract infections and other conditions.
Your doctor will perform an ultrasound between 16-20 weeks to check for physical abnormalities.
You’ll have a glucose screening test to check for gestational diabetes, and possibly another blood test to check for anemia.
A repeat HIV test will be done at the time of the glucose test (New York State mandated).
Between 15-20 weeks, you may have a quadruple screen: a blood test that helps determine your baby’s risk of having certain chromosomal problems (such as Down syndrome) and other birth defects.
You will be offered amniocentesis, an invasive genetic diagnostic test done at about 16-20 weeks. Amniocentesis can determine for certain whether your baby has Down syndrome or other chromosomal abnormalities, neural tube defects and certain genetic disorders.
MASFP (maternal serum alpha-fetoprotein) screen assesses your baby’s risks of open neural tube defects (spinal cord problems).

Third trimester tests (weeks 29-birth, usually 40 weeks)

During your third trimester prenatal visits:

Your doctor may continue to ask for urine samples to check for signs of preeclampsia, urinary tract infections and other conditions.
Between 35-37 weeks, you’ll be tested for a common infection called group B strep. If your test is positive, you’ll be given antibiotics during labor to help keep you from passing on the bacteria to your baby.
Your blood may be checked again for anemia.
If you’re at risk for sexually transmitted infections (STIs), you’ll be tested again for syphilis, chlamydia, gonorrhea and HIV.
If you were found to have placenta previa or a low-lying placenta during an earlier ultrasound, you’ll have another ultrasound to check the location of your placenta.
If your pregnancy is high risk or your practitioner becomes concerned about certain problems, you may have additional ultrasounds, a biophysical profile or a non-stress test to make sure your baby is developing well.

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