Prenatal Screening

Each of our pregnant families is offered prenatal screening for Cystic Fibrosis (CF), trisomies (i.e. Downs Syndrome and trisomy 18), and open neural tube defects (NTD). The discussion surrounding these available prenatal screens will occur during your first several visits with us. Whether or not to pursue prenatal screening during your pregnancy is a personal decision requiring an individualized approach.

The prenatal screens listed below are not meant to be diagnostic of trisomies, CF, or NTD, but are highly sensitive in detecting high risk pregnancies that may warrant further testing (i.e. amniocentesis). As a practice, we collaborate with the Division of Maternal-Fetal Medicine and the Foundation for Blood Research (FBR) to make the following screens as well as genetic counseling available to our clients:

Sequential Screen

This screen is offered to clients between 10 weeks 3 days and 13 weeks 6 days. It involves an ultrasound measurement of your baby’s nuchal translucency (NT) or neck fold, and a blood sample from the mother measuring the level of a particular protein that is linked to Downs Syndrome. A second blood test will then be drawn at 15-21 weeks and sent to FBR. At that time, analysis of both blood samples collected in your first and second trimesters along with your baby’s nuchal translucency, will be completed. The results will give you an individualized risk of Downs Syndrome, trisomy 18, and NTD for your current pregnancy. This prenatal screen has a 90% detection rate of Downs Syndrome with a 3% false positive rate, an 80% detection rate of trisomy 18 with a 0.5% false-positive rate, and an 85% detection rate for open NTD with a 3% false-positive rate.

Alpha-fetoprotein (AFP) or Quad Screen

The Quad Screen involves the measurement of AFP and three other hormone levels in the mother’s blood. The amount of AFP in the blood of a pregnant woman can help identify a higher risk for open NTD (i.e. spina bifida and anencephaly). Collected between 15 and 21 weeks of pregnancy, a Quad Screen can also give you individualized risk information regarding Downs Syndrome and trisomy 18. Collection of the Quad Screen involves a simple blood draw at our office during one of your prenatal visits. The detection rate of open NTD with the Quad Screen is 85% with a 3% false-positive rate. The detection rate of Downs Syndrome is 80% with a 5% false-positive rate.

Fetal Survey or High Resolution Ultrasound

This ultrasound, performed at 18-20 weeks gestation, takes a close look at your baby and placenta. Ultrasound is currently considered to be a safe, non-invasive way to assess the growth and development of your baby. By 18-20 weeks gestation, your baby’s organs and major structures are developed. An ultrasound at this time can help us identify any major abnormalities in such organs as the heart, lungs, kidneys and brain, as well as physical structures such as palate, spine and extremities.

During the fetal survey, the ultrasound technician will also assess the amount of amniotic fluid surrounding your baby as well as placenta placement and appearance. This information, along with the baby’s assessment, can give reassurance in the well-being of your pregnancy. The fetal survey is often the only ultrasound you will have during your pregnancy so thoroughness is essential. If initial views are limited or follow-up is warranted for other reasons, you may be asked to return for a follow-up ultrasound at a later date.

Cystic Fibrosis (CF) Carrier Testing

CF is an inherited disease of the mucous and sweat glands. An abnormal inherited gene causes the normal watery mucous of exocrine glands to become thick and sticky, negatively affecting the lungs, pancreas, liver, intestines, and sex organs. In order to possibly make a baby with CF, both parents must be “carriers” of the gene. Because there are no symptoms associated with being a carrier of the CF gene, the only way to identify whether or not you are a carrier is through CF carrier testing.

Cystic Fibrosis carrier testing is to see if soon-to-be parents are at increased risk of giving birth to a baby with CF. Carrier testing is self-administered and done by obtaining a saliva sample by way of cheek swabbing. Although we recommend collecting samples from both genetic parents initially, a mother that “screens negative” for the CF gene warrants no further testing from the father. The test will identify 1 couple in about 800 who each carry the symptomless CF gene. Their baby will then have a 1 in 4 chance of having CF. In the instance where both parents “screen positive” for the CF gene, an amniocentesis or chorionic villus sampling are the only way to diagnose a baby with CF prenatally. Because the test cannot detect all CF mutations, there is a rare chance that your baby will be born with the disorder even after you have screened negative for current identifiable mutations of the CF gene.

The information prenatal screening can offer may be more important to some expectant parents than to others, and many of our clients will opt out of some or even all screens. Reasons for this are individual but may include:

They have no known risk factors (i.e. family history of chromosomal abnormalities or neural tube defects, maternal age is under 35 years old, no history of diabetes, no family history of genetic disorders). It is important to remember, however, many infants affected by neural tube defects or chromosomal abnormalities have no known risk factors.
Identifying these fetal problems ahead of time will not change how they proceed with the pregnancy.
They want to avoid the anxiety they may experience while waiting for screen results.
They want to avoid unnecessary worry and testing that may follow a false-positive result.
They have a personal belief or value system to trust in the well-being of their baby without the need for prenatal screening.
The cost of the screen is not covered by insurance.

If you have any further questions regarding prenatal screening, feel free to contact us or initiate discussion during one of your prenatal visits.