Department of Family Medicine
Ten Questions and Answers on What You Need to Know About Birth Defects
WHAT IS A BIRTH DEFECT?
The term birth defect is used to describe a variety of disorders ranging from a minor abnormality to a major physical deformity. They may be evident at birth, but may also be detected before birth or later in life.
HOW COMMON ARE BIRTH DEFECTS?
Of every 100 births, there will be three minor and one major birth defect.
WHAT CAUSES BIRTH DEFECTS?
Birth defects may arise with no apparent cause, may be inherited from parents or may be caused by some influence in the environment such as infection, exposure to chemicals, drugs, or radiation. Only 35% of birth defects have an explanation in chromosome defects, hereditary patterns, biochemical abnormalities, infectious disease, or environmental agents. The other 65% of birth defects are completely unexplained. Birth defects produced in laboratory animals by various chemicals are of scientific interest; but human data and animal data often disagree.
HOW DO YOU DETECT BIRTH DEFECTS?
Birth defects may be detected in several ways. Some can be detected before birth through ultrasound, chorionic villi sampling (CVS), amniocentesis or by a blood test called maternal alpha-fetoprotein (AFP). Other birth defects may not be detected until school age or later when specific problems arise with require further testing and evaluation (hearing, vision, diabetes, etc.).
WHAT ARE THE KNOWN CAUSES OF BIRTH DEFECTS?
- Radiation - Every woman and man planning to have children should protect themselves from unnecessary radiation. The most common source is diagnostic medical and dental x-rays. Monitoring is important where workers may be exposed to radiation on the job.
- Cats - Carry a parasite called Toxoplasma which can be transmitted through their feces to pregnant women. The parasite enters through contaminated food or close contact. In a small percent of pregnancies, Toxoplasma can infect the mother's placenta and the baby, resulting in birth defects including mental retardation and blindness.
- Viruses - German measles is one of the very few viruses which can cause serious birth defects. These are prevented by increasing use of rubella vaccine.
- Tobacco and Alcohol - Use during pregnancy may produce premature birth, low birth weight and poor mental development. Avoiding the use of tobacco and alcohol is very important and should be discussed with your physician.
- Genetics - Each person's blood-line contains good and bad genes; first cousin marriages run a risk of a double-dose of lethal or bad genes in the offspring. Down Syndrome is one of the most common chromosome defects. It occurs more often in pregnancies among older women but can occur in any pregnancy for no apparent reason.
CAN CHEMICALS CAUSE BIRTH DEFECTS IN HUMANS?
The major chemicals that are known to cause birth defects are prescription medications which your doctor knows about. These include thalidomide, isoretinoin, valporic acid, cancer chemotherapy agents and a few others. Of major concern to birth defects are lead and mercury. For the most part these have been controlled but still can occur in contaminated well water or buildings with old peeling paint.
WHAT ABOUT PESTICIDES?
There has been much speculation in the media concerning the possible association between pesticides and birth defects in humans. Unfortunately this speculation has not been backed up by solid scientific evidence. One exception is DBCP, a fumigant, which has caused reproductive problems at high exposure levels in men. This was shown in their sperm. With time and avoidance DBCP effects on sperm disappeared. In the meantime, more case/control studies are needed to detect any evidence of reproductive damage by commonly used pesticides.
CAN BIRTH DEFECTS BE PREVENTED?
Exposure to known causes of birth defects should be avoided. The most common factors to be avoided are unnecessary medications, smoking and alcohol consumption. Risks for one group of serious birth defects (neural tube abnormalities - spina bifida, anencephaly) can be significantly decreased by taking folic acid prior to conception and throughout the pregnancy (at least 0.4 mg/day).
Prenatal detection of birth defects is available in cases of Down Syndrome, spina bifida, anencephaly, and others. Your risk of having a child with certain kinds of birth defect is higher especially if there are prior birth defects in your family or marriage between blood relatives; this risk can be estimated by your physician with help from a genetics specialist.
ARE BIRTH DEFECTS INCREASING?
There is good evidence that birth defects, as measured in this country over the past 20 years, are decreasing or remaining the same. Some categories such as heart defects are showing a numeric increase; however experts explain the increase as a result of better diagnostic procedures for minor defects. In fact, neural tube defects, the most sensitive indicator of environmental fetal damage, are decreasing over the past 15 years here and in Europe. Another good sign is the decrease of stillbirths.
WHERE CAN I GET MORE INFORMATION CONCERNING BIRTH DEFECTS?
The best source of information is your personal physician. In fact, write down your questions before each visit during pregnancy, so that you won't forget to ask. Scientists have learned more about birth defects but 65% of these events remain unexplained. Reproduction is not free from biologic error in humans or other species.