The egg and/or sperm can be compromised by environmental conditions which cause genetic damage that can lead to a viable but defective fetus. Preconception, mutagenic effects on either the paternal or maternal side can be caused by environmental contaminants causing chromosomal anomalies and new mutations. Environmental tobacco smoke has been associated with spontaneous abortion, premature delivery, and low birth weight and is considered to be a human growth retardant. Cocaine and other drug use can lead to an infant with addictions, congenital abnormalities, low birth weight, and slowed neurological and behavioral development. Chronic alcoholism can lead to spontaneous abortion, mental retardation, congenital heart disease, and slow growth. Poor maternal nutrition potentially can compound the effects of environmental hazards which can cause problems at conception and also in the fetus.
The placenta is a semi-permeable membrane whose circulation is established around day 17 after fertilization. It becomes a very important route of exposure for the fetus to a variety of contaminants. During the 6-week period that occurs after the beginning of the placental circulation, exposure to a variety of environmental chemicals can cause profound systemic damage, well beyond that which would be expected from the usual response to a given dose of the chemical. This is a particularly vulnerable time for exposure to environmental pollutants, typically when the woman may not know that she is pregnant and therefore would avoid specific environmental hazards.
Low-molecular-weight compounds such as carbon monoxide, fat-soluble compounds such as polycyclic aromatic hydrocarbons and ethanol, and other compounds such as lead, easily cross the placental barrier. These maternal contaminants can have come from the past and been stored in the body or they can be part of the current exposure. The placenta has a limited ability to detoxify chemicals. Some water-soluble and high-molecular-weight compounds can also be a problem, because they may cross the placental barrier. An example would be bisphenol A (BPA), a chemical compound which has been used in producing plastics, as a fungicide, as an antioxidant, as a flame retardant, in rubber, and as a polyvinyl chloride stabilizer. This chemical migrates into the environment, especially in water. The journal Reproductive Toxicology published a warning in August 2007 that BPA can likely cause various human reproductive disorders. A National Institutes of Health (NIH) panel in August 2007 stated that BPA could cause some risk to the neurological development of infants and children. (See endnotes 67, 68.)