Inbreeding effects on human reproduction in Tamil Nadu of South India

A prospective investigation of inbreeding effects was carried out during 1969-74 on representative samples from rural and urban populations of Tamil Nadu in southern India. Altogether, 14243 pregnancy terminations were observed. Forty-seven per cent of the rural women and 29% of urban were consanguineously married; in 80% or more of these marriages the spouses were first cousins or more closely related. The differences between the consanguineous and non-consanguineous marriages were studied with respect to total foetal loss rates, neonatal, infant and perinatal and extended first-year mortality rates; in these cases the differences were quite small and unlikely to have practical importance, though some attained statistical significance. Differences for duration-specific foetal loss, sex ratio and incidence of congenital malformations were not statistically significant. When studied alternatively in terms of the regression of the incidence rate on the inbreeding coefficient, again most regression coefficients were mostly positive but did not reach the 0.05 significance level. Taking into account the background of the population studied, the methodology adopted, and the lack of significant patterns by type of parental consanguinity, the most reasonable conclusion is that the continued practices of consanguinity over several generations have narrowed the differentials of human reproduction and of its wastage among various types of marriages based on parental consanguinity.