The purpose of obstetrics is to maintain the health of the pregnant woman and to ensure optimal health of the fetus. Preconception and postconception risks exist for both mother and child. Certain fetal and maternal conditions have been shown to have environmental and genetic components.
Two determinations must be made when a physician responds to a patient’s concerns about a specific exposure: (1) whether any quantity of the toxicant has known adverse effects on reproduction in humans and (2) whether the substance is present in sufficient quantity to affect the patient or population exposed. This issue is complicated in humans by the high natural spontaneous abortion rate of 15-30%, which makes determining the specific reproductive effects in humans difficult without studying large groups. Thus, reviewing the following criteria is useful for establishing a possible cause and effect:
The exposure must precede the outcome (eg, eliminate temporal ambiguity).
A dose-response effect is observed (ie, more severe effect with increasing dose). Thresholds may occur.
Plausible physiologic and biologic mechanisms: For example, positing that a major change in organ formation was due to late-trimester pesticide exposure would not be plausible because organogenesis would have been completed before the exposures.
Findings should be replicated in more than one study or population.
Cause is more strongly suggested if the effect is an independent variable after all possible confounders are eliminated.
Some researchers have recently suggested that any hypothesized toxicant should be compatible with current existing models of development and should include cumulative risk.
Reproductive risk of toxicant exposure includes fetal effects, especially congenital anomalies. The rate of congenital anomalies in the general population is 3% for defects that are detectable at birth in live-born infants and 6% for defects detected by the end of the first year of life. Because the baseline risk is small, if an exposure conveys a modestly increased risk, a large population of infants is required to detect an increase in anomalies. In addition, the gestational window is critical because exposures outside certain gestational periods may be nontoxic, while the same doses can cause devastating results within the window.
This article provides a summary of many psychosocial and environmental risks during pregnancy. The complex interplay of (1) genetic, (2) environmental, and (3) social factors requires sophisticated and thoughtful interventions on the part of health care providers.