Causes of Birth Defects

Posted: 15. August, 2011 Comments Off

Occasionally during the delivery process, a birth defect like cleft lip is discovered, which went undetected on antenatal ultrasound. In these instances, the parents, who are dealing with an unexpected outcome, may instinctively look for something the mother may have been exposed to during pregnancy. Without a doubt, certain environmental toxins can cause a plethora of birth defects, but many birth defects are considered multifactorial, meaning that multiple causes contributed to the process rather than one specific cause.

Birth defects, also called congenital anomalies, can range from mild to very severe and not compatible with life, meaning the baby may not live. The main causes of birth defects are environmental exposures and genetics. Many times the causes are unknown. Birth defects are seen in all parts of the world. The “background rate” for birth defects has been reported as 3 to 4 percent in the general population. This means that anyone has a 3 to 4 percent chance of having a baby with a birth defect.

Here is a short list of possible environmental or external exposures that can contribute to congenital anomalies:

- Medications. Accutane, Coumadin, alcohol, valproic acid
- Infections. German measles, toxoplasmosis, cytomegalovirus, herpes simplex
- Maternal disease. Diabetes
- Heat. Fever, external prolonged heat exposure
- Heavy metals. Lead, mercury

Another major cause of birth defects is chromosomal or genetic in nature and thereby hereditary. When there is suspicion of potential birth defects caused from a chromosomal or genetic transmission, there are early prenatal tests that can be performed to aid in the diagnosis. The following is a list of early prenatal testing for some congenital anomalies:

- Alpha-fetoprotein. This protein is secreted by the fetal liver and will be at abnormal levels in certain spinal cord and abdominal wall defects. With a Tetra Screen, the alpha-fetoprotein is drawn in addition to a human chorionic gonadotropin (hCG), estriol, and inhibin. During pregnancy, the estriol and inhibin levels are altered by the placental tissue. This level, depending on the laboratory, can be drawn from maternal blood between the fifteenth and twenty-first week.

- Chorionic villus sampling (CVS). Chorionic villus sampling is a sampling of the placental tissue early in the gestation. This tissue is then tested for chromosomal anomalies. This test is usually done between the tenth and thirteenth week, which is earlier than amnio¬centesis, discussed below. The tissue sample is obtained by inserting a needle through the maternal abdomen and then through the uterus into the placenta. It can also be performed by inserting the needle through the cervix rather than the abdomen. Because of its invasive nature, this procedure carries an increased risk of miscarriage or fetal mortality of 0.2 to 0.3 percent. CVS will not detect all congen¬ital anomalies. On occasion some of the cells within one sample may be abnormal while others are normal. Many of these cases prove to have normal gestations. Because CVS testing is not as commonly done as amniocentesis, you should find an institution with significant experience in performing the required procedure. This testing should be reserved for those pregnancies where the earliest possible detection of an anomaly is imperative to the parents and the risks are outweighed by the benefits.

- Amniocentesis. This procedure involves inserting a hollow needle through the abdomen and uterus into the amniotic fluid. Approximately 5 to 10 cc of fluid is removed and sent to a lab for evaluation of fetal skin cells that are floating in the fluid. Chromosomes from these cells are evaluated for chromosomal integrity and number. Amniocentesis can be performed for chromosomal study, to evaluate for infection, to determine a spinal cord defect such as spina bifida, and to evaluate fetal lung maturity in the third trimester. The risk of miscarriage following this procedure is approximately 1 in 200, but some feel it may actually be more like 1 in 600. While this test is done later than CVS, it is generally deemed safer than CVS. Amniocentesis is performed between the twelfth and fourteenth weeks but can be performed at any time during the pregnancy with similar risks. In the latter half of the second trimester, the risks of puncturing the placenta, umbilical cord, and fetus are greater, but the procedure is still deemed safe under the proper protocols.

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