HOW TERATOGENS CAUSE BIRTH DEFECTS
The life cycle of literature runs from birth through infancy, childhood, adulthood, middle age, and old age culminating in death. It is the subject of art, literature, and philosophic reflection. But the late and early twentieth century added some additional components to our life cycle. There is the peri-fertilization period when sperm or eggs form, unite, and a pre-implantation embryo forms. It leaves the oviduct and implants in the uterus. Those events from fertilization to implantation take about five days. The next fifty days are associated with something called organogenesis. The body symmetry is laid out; head vs. tail, dorsal (back) vs. ventral (belly), left vs. right side, and the various systems are established producing organs. After the 55th day we become a fetus and enlarge and perfect those organ systems.
Here’s the problem. A woman does not look pregnant during those first 55 days. She may not even be aware she is pregnant for three or four weeks after fertilization. It is the most vulnerable stage of her pregnancy because there are agents that can interfere with organ formation. Such agents are called teratogens. The most well known teratogen was thalidomide, an over the counter tranquillizer made in Germany and sold to millions of people in Europe in the late 1950s and early 1960s. It led to the formation of 8,000 babies with missing or deformed arms or legs and other birth defects and an unknown number of aborted embryos that were incompatible with further life. The US was lucky, Dr. Frances Kelsey at our Food and Drug Administration felt it had not been tested sufficiently. She did not like reports of long-lasting constipation and peripheral neuritis (numbness or tingling sensations of the arms and legs) reported in Germany. Despite howls of protest about overregulation and government red tape harming industry from the American company hoping to market it, she stuck to her role as a protector of public health.
There are other agents that damage organ formation. Alcohol leads to a fetal alcoholism syndrome. Exposure of the pregnant woman in early pregnancy with German measles can lead to damaged hearts and brains. Parasites in feces of household pets (toxoplasma) can cause such damage. X-rays (especially exposure to occupational or repeated doses) can be damaging to an embryo. What does this tell us? It tells us that women need to protect themselves in early pregnancy when they are most at risk. They should have their husbands clean up the cat or dog excretions. They should avoid over the counter self-medication or prescription drugs unless they have asked an important question to their physicians: “Has this product been tested for teratogenicity?” Memorize it. Write it on a card and keep it in your purse. Most physicians, health providers, and pharmacists are conscientious and they will look up that possibility for you.
As in most concerns about our human biology, it is not easy to test everything new entering the market. Testing on pregnant mice and rabbits is one way to see if new products damage organ formation. We need that regulation to prevent future disasters.