Table IV.

Temporal trend of women’s reproductive span: pooled data from 10 countries.

Birth cohort	Age at menarche	Age at natural menopause	Biological span	Age at first birth	Effective Span
Before 1930	13.54	49.94	36.40	27.25	22.69
1930–1939	13.39	50.37	36.98	26.26	24.11
1940–1949	13.10	50.53	37.43	25.25	25.28
1950–1959	13.03	50.42	37.39	25.81	24.61
1970 onward	12.60	50.50	37.90	27.38	23.12

All data are in years.