Pcb Effects Early in Life Still Unclear

NEW YORK (Reuters Health) - The findings from a new study suggest that exposure to polychlorinated biphenyls (PCBs) in the womb, via the mother's blood, reduces fetal growth, whereas those from another suggest no effect. Both studies are reported in the journal Epidemiology.

Previous reports have suggested that exposure to high levels of these common environmental contaminants adversely affects early growth and development. The effect of more moderate levels of PCB exposure, however, is unclear.

Dr. Irva Hertz-Picciotto, from the University of California at Davis, and colleagues measured PCB levels in samples taken from 399 pregnant women in the 1960s, the decade before the industrial use of PCBs was banned. These levels were then correlated with the growth outcomes of their children up to 5 years of age.

In male and female infants, increasing PCB exposure was tied to a reduction in head circumference. In male infants, birth weight fell as PCB exposure rose, whereas in female infants, the duration of pregnancy dropped as exposure increased.

At 5 years of age, prenatal PCB exposure was associated with increased growth in girls, but had no effect in boys.

The finding of reduced birth weight in male infants with higher PCB exposures in the womb, even after duration of pregnancy at time of birth was factored in, "suggest that some PCBs may differentially affect the...growth of male fetuses," the authors conclude.

In a similar study, Dr. Matthew P. Longnecker, from the National Institutes of Health in Bethesda, Maryland, and colleagues correlated PCB levels in 1034 pregnant women with the growth outcomes of their offspring. As in the first study, the women were pregnant before PCB manufacturing was banned.

PCB exposure in the womb appeared to have no effect on preterm birth, birth weight, or length of pregnancy. There was evidence of a link between PCB exposure and small size at birth, but the findings were not conclusive and are difficult to reconcile with the lack of effect on birth weight.

"Why results for birth weight vary across studies in populations with similar levels of exposure remains unclear, but may be due to the specific mixture of PCBs involved or to the effects of other contaminants or nutrients," the researchers hypothesize.

SOURCE: Epidemiology, September 2005.