Abstract

The effects of inbreeding on the incidence of congenital anomalies and measurement at birth of offspring were explored on the basis of a prospective survey done during 1969 to 1974. The pregnancies of over 20 000 married women from rural and urban samples in North Arcot District were identified and followed up through routine home visiting once every 5 weeks by qualified women investigators. Of all marriages, 47% in the rural areas and 29% in the urban were consanguineous. The average inbreeding coefficients in the rural and urban areas were 0·0371 and 0·0204, respectively; these are significantly higher than those prevalent in most parts of the world.

For purposes of statistical analysis, marriages were classified into four groups based on degree of consanguinity. Women in these four marriage groups were similar in terms of major social, economic, and other demographic factors, and in maternal variables, such as the time since the last pregnancy, place of delivery, and attendant at delivery.

No significant differences existed in the incidence of congenital anomalies among offspring between the consanguineous and non-consanguineous marriages in the rural or in the urban area. Neither were any significant trends seen by degree of consanguinity, or by birth order, or by the different age groups. The types of malformations and their frequency seen in the consanguineous and non-consanguineous groups were similar. There were also no significant differences observed by type of marriage in both areas in gestational age, birthweight, body length, head circumference, or chest circumference. The fitting of exponential curves relating inbreeding coefficients to these indices led to regressions that do not attain statistical significance. It is suggested that long term inbreeding does not lead to appreciable effects on fetal growth and development.