Neural tube defects in Eastern Ontario and Western Quebec: demography and family data.

This paper reports the results of a study of families in the Eastern Ontario/Western Quebec region who had a child born with a neural tube defect during the years 1969-1981. As in several other geographic areas, the prevalence of neural tube defects at birth has fallen from previous levels. However, there was no evidence of further decline during the period of study. Socioeconomic and ethnic influences were noted, but there was no evidence of seasonal variation or any correlation with maternal age or parity. There was support for a causative role of maternal fever in some cases. The rates of miscarriage varied between pregnancies before and those after the proband, and there was an excess of males born prior to the proband. Family studies showed a 2.4% risk for sibs born after the proband and an excess of affected relatives on the maternal side. Knowledge of rates of occurrence in relatives is useful for counseling and the interpretation of the results of alpha-fetoprotein screening.