Frequency and inheritance of twinning have been studied from urban and rural parts of Madhya Pradesh. Family data conform to previous findings by other authors, for other countries, that DZ twinning is influenced by the mother's genotype.

Of special interest has been a rural family in which a female, herself a cotwin of DZ pair, married twice, each time giving birth to DZ twins.

The high rate of twinning in rural areas is suggested to be due to higher coefficient of inbreeding, better physical condition of mothers on the countryside, higher mean birth order, and higher mean age of mothers. Lack of family planning may have also played a role.