Reduced fetal growth in methadone-maintained pregnancies is not fully explained by smoking or socio-economic deprivation.

Aim: To determine if reduced fetal growth in infants of opioid-dependent mothers prescribed methadone maintenance in pregnancy is explained by cigarette smoking or socio-economic deprivation.

Design: Retrospective cohort study.

Setting: Inner-city maternity unit in Scotland.

Participants: A total of 366 singleton infants of methadone-prescribed opioid-dependent mothers compared with the Scottish birth population (n=103 366) as a whole.

Measurements: Primary outcome measures were birth weight and head circumference.

Findings: In infants of methadone-prescribed opioid-dependent mothers mean birth weight was 259 g [95% confidence interval (CI) 214-303 g; P<0.0001] less, and mean head circumference 1.01 cm (95% CI 0.87-1.15 cm; P<0.0001) less than in controls, allowing for gestation, cigarette smoking, area deprivation, infant sex and maternal age and parity. This represents an adjusted difference of -0.61 (95% CI -0.52--0.71; P<0.0001) Z-score in mean birth weight and -0.77 (95% CI -0.66--0.89; P<0.0001) Z-score in mean head circumference.

Conclusions: Reduced fetal growth in infants of opioid-dependent mothers prescribed methadone maintenance in pregnancy is not fully explained by cigarette smoking, area deprivation, maternal age or parity.