Prenatal Testing

As part of your prenatal care, your doctor or midwife will suggest several different tests. These tests give information on how you and your growing baby are doing and can help you prepare for a healthy future.

Routine tests are those that happen during your regular prenatal checkups to help your doctor or midwife know how you and your growing baby are doing. Routine tests include:

• Urine tests to check for urinary tract infections and signs of preeclampsia or other pregnancy-related problems
• Cervical and vaginal tests to check for signs of cervical cancer, Chlamydia, or gonorrhea, Late in your pregnancy (34 weeks or later), you should also have a Group B strep test to see if you need treatment to protect your baby from this bacteria during birth.
• A glucose screening test, usually done between 24 and 30 weeks of pregnancy, which checks for signs of gestational diabetes.
• Other blood tests to determine your blood type and Rh factor, check for anemia, and to see if you have (or are at risk for) rubella, chickenpox, syphilis, or hepatitis.
• You may also have a blood test to see if you have HIV, the virus that causes AIDS. The Centers for Disease Control (CDC) recommends that ALL pregnant women be offered an HIV test. Why? Because if you have HIV, your baby can get it from you during pregnancy, labor, or breastfeeding. But if you get treatment, you can lower the chance that this will happen. Treatment will help you stay healthy, too.

Early in your pregnancy, your doctor or midwife will discuss prenatal tests that aim to detect the risk or presence of a birth defect or serious disease in your developing baby. These testing options are summarized below.

• Cystic fibrosis (CF) carrier testing – can be performed at any time before or during pregnancy
  • This blood test tells whether you carry the altered gene that causes CF. Your baby is at greater risk for having CF only if both you and the baby’s father are carriers.
  • Results apply not only to this pregnancy - but also to any future pregnancy that you and your partner have together.
• 1st trimester maternal serum screening – done at 10 to 13 weeks
  • Paired with an ultrasound, results from this blood test calculate your chance of having a baby with Down syndrome. 
  • The screening can detect about 85% to 90% of pregnancies affected by Down syndrome.
• 2nd trimester maternal serum screening – done at 15 to 22 weeks
  • Results from this blood test calculate your chance of having a baby with Down syndrome, trisomy 18, or a neural tube defect (NTD).
  • The screening can detect about 75% of pregnancies affected by Down syndrome, 60% of those affected by trisomy 18, and 85% of those affected by an NTD.
• Integrated maternal serum screening – spans 10 to 22 weeks
  • This test is a combination of 1st and 2nd trimester serum screenings. It looks at the two results together to create a clearer picture of your baby’s risk for Down syndrome, trisomy 18, or a neural tube defect (NTD).
  • Sequential screening is a stepwise version of integrated screening. It uses 1st trimester results to help women choose to either continue with 2nd trimester serum screening or have additional 1st trimester testing.
  • The screening can detect about 90% of pregnancies affected by Down syndrome, 60% of those affected by trisomy 18, and 90% of those affected by an NTD.
• Chorionic villus sampling (CVS) – usually done at 10 to 13 weeks
  • CVS test requires a small sample of the placenta, and can cause miscarriage. With an experienced doctor, this happens in fewer than 1 out of 300 to 500 procedures.
  • CVS is more than 99% accurate in identifying genetic disorders.
• Amniocentesis – usually done at 15 to 20 weeks
  • Amniocentesis requires a small sample of the fluid surrounding your developing baby (the amniotic fluid), and has an very low risk of miscarriage. This happens in fewer than 1 out of 300 to 500 procedures, or less than 0.002% of the time.
  • Amniocentesis is more than 99% accurate in identifying genetic disorders. Amniocentesis can also detect neural tube defects that affect the spine and brain.