Pattern of menstrual cycles and incidence of congenital malformations.

An analysis has been made of the general reproductive characteristics of mothers, including the temperature curves of preconception and conception cycles, in a prospective study which ended in the birth of 22 malformed infants and 894 normal infants. The differences observed have shown that the mothers of malformed infants had their first menstrual period at a later age (13.4 vs 12.8 years), their menstrual cycles were more often irregular (77% vs 40%) and lasted longer (32.9 vs 30.1 days). Moreover, they had a longer hypothermic phase during both their preconception cycle (21.7 vs 17.6 days) and during their conception cycle (24.0 vs 18.1 days), as well as a longer temperature rise during their conception cycle (3.7 vs 3.0 days). By taking into account the relation between these variables, we have been able to show that increased risk of malformation is associated with increase in the length of the hypothermic phase and the temperature rise of the conception cycle.