Low Birth Weight Across Generations

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Early work described the correlation between birthweights of mothers and their infants. The study of other fetal growth parameters, including length and head circumference demonstrated that infants of low birth weight mothers were both shorter and lighter than infants of larger mothers, but that the infants were normally proportioned. In ensuing studies, birth certificates of infants born in Tennessee between 1979 to 1984 were matched with those of their mothers, who were born in Tennessee between 1959 to 1966. Maternal and infant birth weights were again shown to be correlated. In addition, women who were themselves of low birth weight were up to four times as likely to have a small-for-gestational age infant as were women who weighed 4000-4499 grams at birth, but low birth weight women were less than twice as likely to have a preterm infant. A group of Swedish women, born from 1955 to 1965, was next studied. Women who themselves were small-for gestational age at birth were at increased risk of giving birth to both small-for-gestational age and preterm infants. Women who were preterm at birth were not at increased risk of either outcome. Among women born in the Danish Perinatal Study (1959-61), women born SGA were found to be at doubled risk of having an SGA child, but women born preterm were not at increased risk of giving birth to a preterm child. In addition, women who were small-for-gestational age at birth were at increased risk of developing hypertension during pregnancy. Independent of maternal size at birth, paternal size at birth was found to be associated with fetal growth, but not with duration of gestation. Girls who were born from 1959-66 as subjects in the Philadelphia and Providence cohorts of the Collaborative Perinatal Project were followed-up in adulthood, and their pregnancy outcomes ascertained. Data analysis from these women is currently underway. Initial analyses evaluated the relative contributions of the birth characteristics of the mother and those of older siblings on the birth characteristics of the youngest sibling. Both the mother's own SGA status at birth, and the SGA status of older siblings each predicted SGA status of the youngest sibling. Although having a preterm older sibling predicted preterm birth in the youngest sibling (odds ratio=5.5), having a preterm mother did not (odds ratio=1.0). There were no interactions between maternal and older sib birth characteristics.