The incidence of triplets and higher multiple births in some rural and urban populations in Western Nigeria

SUMMARY In a study of triplets and higher multiple births in Western Nigeria, the incidence of triplets was found to be approximately 1–6 per 1000 maternities. The expected incidence calculated by Hellin's ‘law’ was higher than the observed incidence. The twinning and triplet rates in Western Nigeria were found to be approximately 4 and 16 (i.e. 42) times the corresponding rates in U.K. and U.S.A. Using data on sex the method described by Allen (1960) indicated that there was a relatively higher proportion of trizygotic triplets in the Nigerian population.