Period between ovulation and birth.

Because dates of coitus, ovulation, and fertilization are usually unknown, examination of the duration of gestation in a large series of women is necessarily based on the period of amenorrhoea from onset of menstruation to birth. The considerable variation in this period is due partly to variation in the interval between onset of menstruation and ovulation, and partly to variation in the time between ovulation and birth. In this communication we examine the period between ovulation and birth, which has been estimated for each of 763 women by: