GENETIC SCREENING

Birth defects occur in 2-3% of the general population and the severity can be categorized as minor or major malformations. Certain risk groups such as couples with infertility may be at a greater risk for having a baby with such defects (regardless of infertility treatment) due to the cause of infertility including advanced reproductive age (decreased egg reserve), sperm deformities or being a carrier of certain genetic diseases. Genetic screening is utilized to identify individuals who are at an increased risk, so that advanced testing can be offered prior to or during the pregnancy for final diagnosis.
 
Although genetic screening has been available for many years, its application has significantly increased with the advent of new genetic tests, increased awareness and our understanding of the pathophysiology of various diseases. Currently, there is no single genetic test that identifies all the risk factors for a couple, but a number of different screening tests are offered based on specific risk factors. Genetic testing along with risk assessment should ideally be done prior to the initiation of the pregnancy, but 50% of pregnancies in the United States are unplanned and therefore genetic screening is commonly offered during the pregnancy.
 
Currently pregnant women are offered genetic screening for a number of diseases based on their personal risk. Once pregnancy is confirmed, testing for blood type, vaccination status, complete blood count, urine analysis and infectious disease testing have become routine. Additional testing is offered based on racial and social background and include the following:
 

• Sickle Cell Disease: Patients with African-American ancestry should be screened via hemoglobin electrophoresis for carrier status of this disease, as one in 10 may be a carrier.
• Cystic fibrosis (CF): It is estimated that 3% to 10% of Caucasians carry an effected CF gene, but do not have the actual disease because a person must inherit two defective CF genes, one from each parent, to develop the disease. CF is the most common inherited disease in Caucasians, and more common in those of northern or central European background and Ashkenazi Jewish background.
• Thalassemia: People of Turkish, Greek, Italian, Mediterranean or southern Asian descent experience a high incidence of this disease. Patients can have a complete blood count (CBC) with mean corpuscular volume (MCV) to rule out the possibility of thalassemia. An MCV of <80 should be evaluated further by hemoglobin electrophoresis. About 3% of the world’s population carries a gene for thalassemia.
• Tay Sachs: This disease has a high incidence in Eastern European Jews and French Canadians.

 
Once the genetic screening test comes back positive prior to pregnancy, the male partner should be tested to further define the risk for a planned pregnancy. If the male partner screens negative for the same disease, the risk of having an affected child is very low. If testing is being done for the first time during pregnancy, male partner should still be tested to assess the actual risk and specific diagnostic testing can be offered. If the screening test comes back positive in pregnancy, partner is tested and if he tests positive, genetic testing during the pregnancy is offered for diagnosis.
 
If screening of both partners is positive prior to pregnancy, prenatal testing can determine if the unborn child is affected with the disease. Preimplantation genetic diagnosis (PGD) is one of the methods used along with in vitro fertilization (IVF) treatment to test embryos for specific genetic disorders prior to their transfer to the uterus. With PGD testing, one of the stem cells (blastomere) is removed from each embryo and certain genes in the DNA are amplified and compared to a standard DNA. Once genetically normal embryos are identified, they are transferred to the uterus and the risk of having an affected child is significantly diminished.
 
There are two genetic tests available during the pregnancy and include chorionic villus