Differential effects of maternal heroin and methadone use on birthweight.

An analysis of birthweights of 337 neonates in relation to history of maternal narcotic usage was undertaken. Mean birthweight of infants born to mothers abusing heroin during the pregnancy was 2,490 gm, an effect primarily of intrauterine growth retardation. Low mean birthweight (2,615 gm) was also seen in infants born to mothers who had abused heroin only prior to this pregnancy, and mothers who had used both heroin and methadone during the pregnancy (2,535 gm). Infants born to mothers on methadone maintenance during the pregnancy had significantly higher mean birthweights (2.961 gm), but lower than the control group (3,176 gm). A highly significant relationship was observed between maternal methadone dosage in the first trimester and birthweight, i.e., the higher the dosage, the larger the infant. Heroin causes fetal growth retardation, an effect which may persist beyond the period of addiction. Methadone may promote fetal growth in a dose-related fashion after maternal use of heroin.