Pregnancy loss and maternal methemoglobin levels: an indirect explanation of the association of environmental toxics and their adverse effects on the mother and the fetus.

The aim of this epidemiologic study was to point out a relationship between the exposure to products of coal combustion, and complications in pregnancy where one third of causes of stillbirth are still unknown. In the town of Labin (Croatia) a coal-powered thermoelectric power plant is the single major air polluter. We compared the records of miscarriages, premature births and stillbirths in two periods: the control and the exposure period. Data on reproductive loss was based on the records of pregnant women visiting for regular monthly pregnancy checkups. At the time of the epidemiological prospective study, 260 women (n = 138 in the clean period and n = 122 in the dirty period) were considered representative. The data were processed using Chi square and correlation tests. The frequencies of miscarriages and stillbirths were significantly lower in the control than in the exposure period (p < 0.05). Methemoglobinemia and stillbirths recorded over the "exposure" period are significantly higher than in the "control" period (p = 0.0205). The level of methemoglobin in the bloodstream is an worthy biomarker, predictor and precursor of environmental toxics' adverse effects on the mother and fetus, and can indirectly explain the unrecognized level of fetal methemoglobin. Methemoglobin and heme, having prooxidant properties, also cause the early and late endothelial dysfunction of vital organs. Despite our retrospective epidemiological study findings, we emphasize that the rate of reproductive loss represents a hypothetical risk, which needs to be confirmed with further fetal clinical and anatomopatholgical researches about the effects of methemoglobin catabolism products on the fetal CNS.