Reproductive Health Effects

Pesticides may be associated with an elevated risk of specific birth defects, including cleft lip and palate, spina bifida and limb anomalies, as well as hypospadias and cryptorchidism.

Congenital Malformations

From Obstetric Ultrasound: A Comprehensive Guide. Permission granted by
Dr. Joseph Woo.

Generally the fetus (and preconceptionally, a woman’s eggs) is most vulnerable to chemical exposures. The first trimester when organogenesis and formation of major body structures occur represents the most vulnerable and sensitive period as described previously, and can most often result in congenital abnormalities from environmental exposures.

Pesticides. There is evidence that a number of different pesticides can cross the placenta and can therefore potentially affect fetal development and survival.27 There are, however, few epidemiological studies with solid evidence of the effects of in utero exposure to pesticides.

Based on experimental data in pregnant animals and several studies of women occupationally or environmentally exposed to pesticides during early pregnancy, it appears that pesticides may be associated with an elevated risk of specific birth defects depending on timing of the exposure. These include cleft lip and palate,28 spina bifida and limb anomalies,29 as well as hypospadias and cryptorchidism.30

A Minnesota study of agricultural workers and the general population revealed higher rates of birth defects in infants conceived in spring and in areas where chlorphenoxy herbicides were used.31 In Iowa, exposure to herbicides through contaminated municipal water was associated with an increased risk of fetal growth retardation in the general population.32

Organic solvents. Researchers from Toronto’s Hospital for Sick Children conclude from a prospective study of 125 pregnant women that those who were occupationally exposed to organic solvents during pregnancy had a 13-fold higher risk of fetuses developing major malformations compared to controls. Solvents are implicated in the etiology of a variety of birth defects involving the central nervous system, heart, urinary tract, lip and palate.34

Lead. While lead per se is not known to cause congenital defects from prenatal exposure, it does appear to have effects on fetal development. Lead is highly neurotoxic to the developing fetus and infant. Even at relatively low blood lead levels (less than 10 mcg/dL), it affects pregnancy outcome and is associated with greater risk of prematurity, low birth weight and fetal growth retardation.35

Canadian Data on Birth Defects

As part of the Great Lakes Health Effects Program, an Atlas of Birth Defects was comprised for the Great Lakes region. The report was only able to conclude that there is considerable geographic variability in the types of birth defects observed in Ontario but that there is little evidence of excess risk at the local level. These data are limited by the fact that they are not able to identify specific causal factors that explain variability in rates of birth defects.36

Given that there are many possible recognized birth defects, many of which are rare and which reflect disruption at different times, as well as interaction with genetic factors, it is not difficult to understand why there is so much uncertainty in defining the risks to fetal development from toxic exposures.

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