Reduced male births in major Italian cities.

The downward trend in the sex ratio at birth that has occurred in several countries over the last 30 years was postulated to signal a deterioration in environmental conditions, particularly unfavourable for male conception and fetus survival. In Italy, in contrast, an upward trend has been observed. Assuming that exposure to reproductive hazards occurs mainly in the major cities, we contrasted the 1970-1995 sex ratio trend for the metropolitan area (defined as the four provinces containing the largest Italian cities) with that for the non-metropolitan area (defined as the rest of the country). In the metropolitan area, the proportion of live-born males showed a negative trend significantly different from the positive trend observed in the rest of the country. Moreover, the stillbirth rate among males was constantly and significantly higher in the metropolitan area. Our results suggest that the decrease in the sex ratio at birth observed in the metropolitan area might be interpreted as a signal of increasing exposure to hazardous environmental conditions for male conceptions and neonates.