The familial incidence of twinning.

Abstract

Summary1. Mothers, but not fathers, of twins are more often themselves twins than expected.2. There appears to be an increased twinning rate among the children of the brothers and sisters of the fathers of twins, and of the sisters of mothers of twins but not among the children of the brothers of mothers of twins. Internal evidence suggests that the increase among the children of the father's sibs is spurious, and is due to under‐reporting of single births on the father's side of the family.