Prenatal tests
Screening or diagnostic?
- A screening test estimates the chance that the fetus has a condition, such as Down syndrome. It can't say for sure.1
- A diagnostic test tells whether the condition is actually there. It uses cells from the fetus or placenta, collected by amniocentesis or CVS.1
Both are offered to everyone who is pregnant.1
Myth: A positive screening test means something is wrong with the baby.
It's natural to read it that way, and many people panic at the result. A positive screen means a higher chance than average, not a diagnosis. A negative screen means a lower chance, but doesn't rule anything out.1 Only a can say for certain, and a genetic counselor can help explain the result.
Genetic screening options
- Carrier screening, before or during pregnancy, checks whether a parent carries a gene for conditions like sickle cell disease or cystic fibrosis.1
- First-trimester screening, at 10 to 13 weeks, combines a blood test with an ultrasound of the back of the fetus's neck.1
- Cell-free DNA testing, from 10 weeks, screens the pregnant person's blood for Down syndrome and some other chromosome conditions. Results take about a week, and a positive result should be confirmed with a .1
- Second-trimester screening includes a blood test at 15 to 22 weeks and an ultrasound at 18 to 22 weeks that checks the brain, spine, face, heart, belly and limbs.1
Gestational diabetes
Everyone should be screened for gestational diabetes. People with risk factors are tested early; everyone else, usually between 24 and 28 weeks.2 It happens when pregnancy hormones get in the way of insulin, and blood sugar rises.2 Risk factors include being overweight, or a large baby in a past pregnancy, high blood pressure and PMOS, but it can happen to anyone.2 It usually goes away after birth, but it raises the risk of diabetes later in life.2
Your choice
Whether to have genetic testing is your decision, and your beliefs and values matter. Some people want to know ahead of time to prepare; others don't. ACOG says there is no right or wrong answer.1
Recap
- Screening tests give a chance; diagnostic tests give an answer.
- Cell-free DNA screening can start at 10 weeks. A positive result should be confirmed with amniocentesis or CVS.
- An ultrasound at 18 to 22 weeks checks the baby's body and organs.
- Everyone is screened for gestational diabetes, usually at 24 to 28 weeks.
- Genetic testing is optional, and there's no right or wrong choice.
Words to know 6
| amniocentesis | A diagnostic test that takes a small sample of the fluid around the fetus. |
|---|---|
| cell-free DNA test | A blood test, from 10 weeks, that screens for Down syndrome and some other chromosome conditions using DNA from the placenta. |
| CVS (chorionic villus sampling) | A diagnostic test that takes a small sample of the placenta. |
| diagnostic test | A test that tells whether a condition is actually present. |
| gestational diabetes | Diabetes that starts during pregnancy. |
| screening test | A test that estimates the chance of a condition. It can't say for certain. |
Educational information, not medical advice. Talk to your doctor about your health.