Twinning rates among women at the end of their reproductive span and their relation to age at menopause;

A review of studies on twinning has shown that dizygotic (DZ) twinning rates among women from general populations characteristically peak at ages 35-39, then decline sharply. Analysis of genealogical data from the Archives of the Mormon Church indicates that women who are dizygous twins themselves or the sibs of dizygous twins have a higher twinning rate among their offspring than do women from the general population. The dizygotic twinning rates of women who are twins or the sibs of twins classified by maternal age also peak at ages 35-39 but remain high at ages 40-44, then decline. It is well known that Negro women have high DZ twinning rates; a less well knwon finding is that the DZ twinning rates of Negro women also remain high after age 39. It has been suggested that high DZ twinning rates at later maternal ages may be related to a delayed age at menopause; However, published reports on age at natural menopause and analysis of our data from contemporary white US women indicate the contrary; Women who have borne unlike-sexed (DZ) twins and Negro women have a lower age at natural menopause then do white women from general populations, and a lower age in comparison with women who have borne like-sexed twins.