The age pattern of fecundability: An analysis of French Canadian and Hutterite birth histories

This paper analyzes the age pattern of effective fecundability from populat ions with no evidence of deliberate fertility control using a new convoluti on model of fecundability. The analysis is based on a sample of Hutterite b irth histories from the mid-20th century, and birth histories of French Can adians from the 17th and 18th centuries. The main findings are as follows: 1) the level of effective fecundability is higher among the French Canadian s compared to the Hutterites; 2) effective fecundability peaks at age 20 fo r the Hutterites, and in the early to mid-20s for the French Canadians; 3) Hutterite effective fecundability declines almost linearly from age 20 to 4 5, and French Canadian effective fecundability declines slowly from its pea k to the early 30s, and more rapidly at older ages; and 4) the duration of postpartum amenorrhea is longer for the French Canadians than for the Hutte rites. Because of the shorter periods of postpartum amenorrhea the Hutterit es have about the same average number of children as the French Canadians, even though the French Canadians have higher effective fecundability.