The environment: Its risks to conception and pregnancy

When people talk about the environment, they typically are referring to the world at large or a defined geographic area. But for every person on this planet, there is an initial environment, one much more finite, that determines his or her destiny. That environment is the reproductive-aged couple. The inhabitant is the unborn child and those gametes that will eventually result in his or her conception.

There are roughly 60,000 chemical substances in use by commerce and industry in Western countries. One thousand more are introduced annually. Yet only 5% have been investigated for their effects on reproduction. The EPA states that at least 50 widespread chemicals affect reproduction in animals, but only four—lead, ionizing radiation, ethylene oxide, and dibromochloropropane—are regulated in the United States, partly because of their effects on human reproduction.

Conception and pregnancy are a series of three microenvironments. Every month, a reproductive-aged woman matures an egg prior to its release in a fluid-filled microenvironment called a follicle. For pregnancy to occur, sperm transported in a microenvironment called semen exits the male reproductive tract and swims into the female reproductive tract. If the egg fertilizes and implants in the uterine wall, it forms a microenvironment called the amniotic sac and receives nutrition from its mother via the umbilical cord. At birth, the infant exits this last in a series of microenvironments and enters the macro-environment of the world at large. Each of the microenvironments I mentioned offers us a window into the environmental risks of conception and pregnancy.

Consider the microenvironment of semen. High bromodichloromethane levels in home drinking water are associated with lower sperm counts and fewer normally shaped sperm. Men living in agrarian areas, where use of pesticides is high, have higher pesticide levels in their blood and semen and lower sperm counts and lower sperm motility than men living further away. Mothers of subfertile men have higher levels of the pesticide, dichlorodiphenyldichloroethylene in their blood, than mothers of fertile men, even if the subfertile men have normal levels, suggesting the problem occurred in utero.

The microenvironment of the follicle is also at risk. Several studies have reported PCBs in the follicle fluid of women going through in vitro fertilization. One report showed women with endometriosis to have higher follicle fluid levels of PCBs than women without the disease. Another study found roughly half of infertile women undergoing in vitro fertilization to have cadmium and PCBs in their follicular fluid. The pesticides p,p'-DDE, mirex, hexachloroethane, and 1,2,4-trichlorobenzene have also been found in follicle fluid at twice the levels found in the patient's blood stream. This means for some infertile women, their maturing eggs are being bathed in concentrated levels of pesticides.

The third microenvironment is the amniotic sac. Both lead and mercury pass through the placenta into the amniotic fluid, directly to the baby, in concentrations nearly identical to his or her mother's blood serum level. That is why pregnant women must limit their fish consumption, which is unfortunate. Why? Consider this. Women who consume an average of 1.2 fish servings per week during the second trimester have children with higher cognition scores than women who eat less fish. The more fish a mother eats, the higher her baby's cognition scores. However, an increase of only 1 ppm of mercury substantially lowered the infant's cognition scores. In addition to the east and west coasts of the United States, 61 million adults live in the eight U.S. states bordering the Great Lakes, which have been publicized as studied sources of mercury and other environmental pollutants. A recent survey revealed 84% of the adults living in these states include fish in their diets; 7% (4.2 million adults) consume fish caught in the Great Lakes. Awareness of consumption advisories among this population was lowest among women.

There is much more evidence to support the potentially negative impact of a mother's environment on her developing baby. Mothers who live within 1 mile of a hazardous waste site bear children who have a 20% increased risk of congenital heart disease over those who live farther away. Within 1/4 mile of a hazardous waste site there is an increased risk of neural tube defects. Babies born to mothers in California who live within 5 miles of where the air is polluted with small particles have babies that are small for gestational age. The spraying of agricultural pesticides around pregnant women, including insecticides sprayed indoors in greenhouses, has been associated with an increased risk of fetal death due to congenital abnormalities, and male pesticide exposure has been linked to an increased risk of miscarriage and preterm delivery.

Lest you think environmental toxins are only a risk in agricultural areas, urban women exposed to higher levels of chlorination by-products in drinking water, trihalomethanes (THMs) in particular, have an increased risk of delivering a stillborn. The immediate reaction might be not to worry because you drink bottled water. But these particular substances are readily absorbed through the skin, and studies show that pregnant women tend to prefer baths to showers and tend to bathe more often. Other studies have shown THMs increase the lifetime risk of cancer in the mother, while different studies show THMs affect a woman's hormone production and shorten her menstrual cycle.

Autism is another potential hazard of environmental toxins on pregnancy. Autism affects 1 in 150 children in the United States. Between 1991 and 1997 there was an astonishing 556% increase in the pediatric prevalence of autism to a level higher than spina bifida, cancer, or Down syndrome. One recent theory suggests the cause is due to increasing levels of mercury in pregnancy. Autism is associated with higher levels of fetal testosterone production and lower levels of fetal estrogen production. Mercury does just that. It interferes with fetal hormones by increasing testosterone and lowering estrogen production.

A final topic is prenatal phthalate exposure. Phthalate is a pollutant found in everything from perfumes to vinyl floors. It is also in the air we breathe. In 2003, Scientists at Columbia University's Center for Children's Environmental Health measured phthalate levels in the personal air samples and urine of pregnant women in New York City and found the substance present in 100% of the air and urine samples. What is the potential consequence? A 2005 study from Rochester, NY, determined that pregnant women exposed to high levels of phthalate had male offspring with smaller penises and a higher incidence of incomplete testicular descent, increasing the child's risk for future fertility problems.

More needs to be done to make physicians and patients aware of the impact the environment has on conception and pregnancy. Protecting the environment not only protects our patients' health today; it also protects the microenvironment of our reproductive-aged citizens, who represent the health of our future.