Incidence of ovulation from the menarche to the menopause: observations of 622 New Zealand women.

Urine samples were collected once weekly for two to four months from 622 normal women. Menstrual cycles were considered to be ovulatory if the 24 h pregnanediol output in the 12 days preceding menstruation was greater than or equal to 5 mumol on one occasion, or if the total excreted on two occasions, one week apart, was greater than or equal to 7 mumol. The incidence of ovulatory cycles increased from 48% in girls aged 10-14 yr to 72% by 20-24 yr, reached a plateau of 98% in women aged 30-39 yr, then declined with the approach of the menopause to 66% in women over the age of 50 yr. In women who were 5-8 yr from the menarche, departure from the parental home was associated with a decline in ovulatory incidence (84% for women living with parents, cf 46% for women living in flats and hostels; p less than 0.01). A similar decline was noted in women over the age of 40 yr who had experienced a break in a previously regular pattern of menstrual cycles (98% for women with regular cyclicity, cf 58% for women with variable cyclicity; p less than 0.001). Hormone patterns consistent with the occurrence of ovulation were seen at all stages from 120 days after the menarche to seven days before the menopause.