Prenatal Genetic Counseling
Is it Right for You?
Genetic Counseling
When planning a pregnancy, or during an early obstetrical visit, your doctor may recommend an appointment with a genetic counselor. Genetic counselors are health professionals who work closely with obstetricians and medical geneticists to provide risk assessment and counseling for couples at risk for having a baby with a birth defect or genetic condition.
Reasons for referral to a genetic counselor:
- Maternal age
- Maternal health condition
- Family history of birth defect or genetic disorder
- Abnormal ultrasound
- Abnormal maternal serum screen
- Environmental exposure (medication, cigarettes, etc.)
- Ethnic background
A genetic counselor will obtain information about your family history, medical history and pregnancy history. The counselor will explain the risks to the pregnancy, if any, based on these histories, as well as any options available for prenatal diagnosis. The risks, benefits and limitations of prenatal diagnosis are reviewed, such that the couple has all the information they need to make an informed decision regarding testing. Since some scenarios can be more complicated than others, the genetic counselor may be a valuable member of the obstetrics team in helping ensure that all available testing is offered and that all necessary testing gets done.
Genetic Screening
A variety of screening tests are available during pregnancy. Some involve screening the mother and/or father for certain health conditions and genetic disorders. Others involve screening the fetus directly, either through ultrasound looking directly at the fetus, or by maternal serum screening, in which protein levels are measured in the mother’s blood that help assess the health of the baby.
Examples of screening tests during pregnancy:
- Maternal Serum screening (first trimester, second trimester or a combination of the two)
- Ultrasound – first trimester nuchal measurement and second trimester anatomy scan
- Fetal echocardiogram (special ultrasound focusing on the baby’s heart)
- Genetic carrier testing of parents based on ethnic background (i.e. sickle cell disease, Tay-Sachs disease, cystic fibrosis)
- Genetic carrier testing of parents based on family history of genetic disease
Screening tests are primarily used to determine which pregnancies may benefit from more comprehensive testing. While the overall reason to screen during pregnancy is to help determine whether or not a pregnancy is developing appropriately, not all screening tests are right for everyone. If your doctor is recommending a particular screening test, and you are not sure if it is right for you, a consult with a genetic counselor may be helpful in understanding the risk, benefits and limitations of that particular test.
Diagnostic Testing During Pregnancy
For some couples, if a screening test is abnormal, diagnostic testing may be recommended. Or, some couples may prefer to opt for diagnostic testing, without the uncertainty of the screening test first. The results of diagnostic testing are more definitive, with far fewer false positives and false negatives. The downside to some diagnostic tests is that there may be a slight risk for pregnancy complication, including miscarriage, associated with them.
Examples of Diagnostic Tests during pregnancy:
- Chorionic Villi Sampling (CVS)
- Amniocentesis
Both CVS and amniocentesis are diagnostic tests which yield definitive results. In CVS, a tiny amount of tissue from the outside of the placenta (which comes from the same fertilized egg as the baby) is obtained for analysis. In amniocentesis, a small amount of fluid is withdrawn from the sac around the baby, and this fluid contains skin cells which have been shed by the baby. From the cells obtained from both CVS and amniocentesis, chromosomes can be analyzed to rule out conditions like Down syndrome (an extra copy of chromosome #21), and DNA can be isolated for possible diagnosis of a particular condition known to run in that family. Some additional biochemical testing can also be performed on the fluid obtained from an amniocentesis.
The bottom line is that no prenatal test can guarantee you a healthy baby. Every pregnancy has approximately a 2-3% risk for complication. But there are several screening and diagnostic tests available to offer guidance and reassurance throughout your pregnancy. A genetic counselor can help you navigate through the complicated path of genetic screening and testing during pregnancy, while still allowing you the autonomy to make the decision that is right for you and your family. There are several genetic counseling centers in the Philadelphia area, including most major hospitals. If you would like to meet with a genetic counselor before or during your pregnancy, ask your obstetrician/gynecologist for a referral.