Inbreeding effects on prereproductive mortality: a case-control study in Saguenay-Lac-Saint-Jean (Québec, Canada) based on a population registry 1838-1971

Effects of inbreeding on the prereproductive mortality, excluding spontaneous abortions, were investigated among offspring of 251 marriages between first-degree cousins (2:2) and 358 marriages between first-degree cousins once removed (2:3) from Saguenay-Lac-Saint-Jean. A control group matched on the demographic and socioeconomic characteristics of the consanguineous marriages was created. The mortality rates were calculated from a computerized population registry. The stillbirth rate was not significantly higher in the 2:2 and 2:3 groups compared with their respective control groups (p > 0.05). Mortality during the first year was significantly higher in both consanguineous groups (p < 0.01) whereas mortality between 1 and 15 years was not (p > 0.05). In Saguenay-Lac-Saint-Jean, less than 1% of the prereproductive mortality, excluding spontaneous abortions, can be attributed to consanguineous marriages. This study is in agreement with previous reports showing that inbreeding had a minor impact in prereproductive mortality.