Adolescent coitus and infant birthweight.

Seventy-nine percent of a group of adolescent mothers reported coitus during pregnancy. There was a significant difference between the mean birthweight and gestational age of infants born to mothers who reported coitus within 90 days of delivery compared to the mean birthweight and gestational age of infants of mothers who reported no gestational age of infants of mothers who reported no coitus within 90 days of delivery. Thirty-nine percent of the variance in birthweight was explained by maternal factors alone, but only 1.0% of the variance in birthweight was accounted for by the interval between last coitus and delivery. Prepregnancy weight (r = 0.380) and weight gain during pregnancy (r = 0.327) contributed 19.1% and 7.4% of the variance in birthweight, respectively.