A study of the fertility of mothers of twins.

Data on all births to Birmingham residents during a ten-year period were used to compare the reproductive history of mothers immediately before and after a twin maternity with that of mothers of similar age and parity before and after a single birth. It was found that mothers of twins were less likely than mothers of singletons to have a subsequent birth if both twins survived, but if only one survived there was little difference between the two groups. If both twins died, however, the likelihood of a later birth was increased. The interval before the next birth was longer than expected when both twins survived and much shorter when both died. The sex of the twins appeared to have little influence on subsequent reproduction, in spite of the fact that for singleton-containing fraternities a further pregnancy was more likely if the first two children were of the same sex than if they were of opposite sexes. The mean interval preceding a twin maternity was almost the same as that preceding a single birth when both twins survived, but it was shorter when one twin died (being similar to that preceding the birth of a singleton who died) and it was much shorter when both twins died.