Factors associated with low birth weight of infants delivered at term.

The singleton births in the 1958 British Perinatal Mortality Survey (Butler and Bonhan, 1963; Butler and Alberman, 1969) were used to study the aetiology of low birth weight of infants delivered at term. After exclusion of macerated stillbirths and infants with lethal congenital defects, 468 infants of 259 days or more gestation and a birth weight which was less than 2500 g were identified. The mothers and their pregnancies were compared with those of the population of 16 994 singleton births. Delivery at term of a low birth weight infant was significantly associated with maternal prepregnant weight, maternal height, maternal smoking, primiparity, maternal employment, low social class, a previous infant of low birth weight, threatened abortion and severe toxaemia. No significant associations were found with illegitimacy, area of residence, previous spontaneous abortion, essential hypertension, mild toxaemia, chronic or acute infections or other conditions. There were significant negative associations with a history of previous large infants and with maternal blood group AB.