Early pregnancy is a time of great excitement. It is also a time of uncertainty: "Is my baby normal?"
Screening for genetic, chromosomal and congenital abnormalities can diminish some uncertainty and help build confidence as women move forward in their pregnancies. While every fetal abnormality cannot be diagnosed or identified prior to birth, most major abnormalities can be identified.
There are many tests available to determine whether a baby has abnormalities. Three major areas of abnormalities are:
- Structural/anatomic defects. Abnormal development of an organ or a part of the body because of environmental influences but also seen in chromosome or genetic disorders.
- Genetic defects. Abnormal functioning of several organs or parts (commonly a disease such as cystic fibrosis) due to abnormal genes passed from the mother or father or both.
- Chromosomal abnormalities. A collection of abnormalities occurring as a consequence of too many chromosomes from either the mother or the father (for example Downs Syndrome).
- Cystic Fibrosis Testing: This most common of gene abnormalities results in an uncommon but quite difficult disease. While 1 out of every 24 people actually carry the gene, the fact that both a mother and a father have to first carry the gene (an approximate 1/525 chance) and then contribute the abnormal gene to their sperm and their egg (a ½ chance each) makes the actual incidence of a baby being affected by CF an unlikely event (approx. 1/2000). Testing is available at preconception and early in pregnancy. The test can be done on either the mother or the father, and if either are negative, their child will not be affected. If both are positive, additional testing can be done to determine whether the fetus is affected.
- Quad Screen: Performed from 15 to 20 weeks in a pregnancy, the quad screen blood test determines the risk of a baby having Downs Syndrome (trisomy 21). Drawn from a mother most typically at 16 weeks, four different blood levels, hCG, Estriol, AFP and Inhibin A, when combined with a mother's age can indicate the likelihood of a baby having Downs Syndrome. Not a diagnostic test (it will not indicate definitively if the baby has Downs Syndrome), the Quad Screen can indicate "high risk" if the calculated risk for the baby having Downs Syndrome is high. The Quad Screen is only a risk evaluation, not a diagnostic (yes or no) test.
- Amniocentesis: Performed early, in the range of 12 to 16 weeks gestation, amniocentesis involves placing a needle through the mother's abdomen and into the fluid around the fetus. Fetal cells drawn up with the amniotic fluid are then grown and analyzed to determine whether the number of chromosomes is normal. This diagnostic test unfortunately can cause the loss of a pregnancy 1/200 to 1/300 times. Sometimes a woman absolutely must know whether her child is affected or not. In such a situation, the amniocentesis is the option of choice despite its high risk.
- Ultrasound: The purpose of an ultrasound primarily is to identify structural or anatomic abnormalities in a fetus such as neural tube defect, heart defects, abnormal kidneys, cleft lip or palate etc. Approximately half of all babies who are affected by Downs Syndrome have some abnormality that can be identified on ultrasound, and it is possible, in the setting of a normal fetal ultrasound at around 18 weeks, to lower a calculated risk by half. An ultrasound can also identify abnormalities in a fetus that increase the risk of Downs.
We encourage you to ask questions on prenatal testing and what they mean for you and your pregnancy.