Prenatal testing is routine in most pregnancies. Screening tests — which pose few or no risks for you or your baby — can identify whether your baby is more likely to have certain conditions. Here's an overview of common prenatal screening tests:
|What it is||When it's done||What the results may tell you||Follow-up
|First trimester screening
|Maternal blood test to measure levels of two pregnancy-specific substances and an ultrasound to measure the size of the clear space in the tissue at the back of a baby's neck (nuchal translucency).
||Between weeks 10 and 14 of pregnancy
||Whether the baby has an increased risk of Down syndrome (trisomy 21) or Edwards syndrome (trisomy 18)
||Chorionic villus sampling or amniocentesis may be recommended to confirm or rule out a diagnosis.
|Maternal blood test to measure four substances that normally come from a baby's blood, brain, spinal fluid and amniotic fluid.
||Between weeks 15 and 20 of pregnancy
||Whether the baby has an increased risk of developmental or chromosomal conditions, such as spina bifida or Down syndrome
||Fetal ultrasound or amniocentesis may be recommended to confirm or rule out a diagnosis.
|Sound waves from a transducer moved over the mother's abdomen are converted into images on a monitor.
||Between weeks 18 and 20 of pregnancy
||Whether the baby has various congenital conditions, whether the placenta is healthy or if the baby's growth and development are on target
||Specialized or targeted ultrasound or other tests, such as amniocentesis or cordocentesis, may be recommended to confirm or rule out a diagnosis.
Prenatal screening tests (PDF file requiring Adobe Reader)
If the results of a screening test are positive or worrisome, your health care provider may recommend a more invasive diagnostic test. Here are the basics on the most common prenatal diagnostic tests:
|What it is||When it's done||What the results may tell you||Safety concerns
|A sample of amniotic fluid is withdrawn from the mother's abdomen with an ultrasound-guided needle.
||After week 15 of pregnancy
||Can identify some chromosomal or genetic conditions, as well as neural tube defects
||Between 1 in 300 and 1 in 500 risk of miscarriage
|Chorionic villus sampling (CVS)
|A sample of the placenta is removed — guided by ultrasound — through a needle inserted in the uterus or a tube threaded through the cervix.
||Between weeks 10 and 12 of pregnancy — earlier than amniocentesis
||Can identify some chromosomal or genetic conditions
||1 in 100 risk of miscarriage
|Cordocentesis (also known as percutaneous umbilical blood sampling, or PUBS)
|A blood sample is taken from the umbilical cord through an ultrasound-guided needle inserted in the mother's abdomen.
||After week 18 of pregnancy
||Can identify chromosomal conditions, blood disorders, infections and restricted growth
||About a 2 in 100 risk of miscarriage
Prenatal diagnostic tests (PDF file requiring Adobe Reader)
If you're concerned about prenatal testing or wonder whether you need specific screening or diagnostic tests, discuss the risks and benefits with your health care provider.
Last Updated: 2010-11-18