Maternal age and overdue conceptions.

Data from the National Survey of Family Growth, Cycles I and II, are used to describe the level and trend in the incidence of births resulting from pregnancies which began later than desired. Overdue births were about 12 per cent of the total in 1973-75, and the trend was upward, especially among mothers over 25. Pregnancies 12 months or more overdue were more common among mothers over 30 than younger mothers. Analysis of waiting times to conception among women who scheduled intercourse for the monthly fertile period suggests that a decline in fecundity after age 30 may be a factor in overdue births.