Maternal methadone dose during pregnancy and infant clinical outcome.

In recent decades there has been an increase in the methadone dosages prescribed for opioid dependent women during pregnancy. Using prospective longitudinal data from a cohort of 32 methadone exposed and 42 non-methadone exposed infants, this study examined the relationship between maternal methadone dose during pregnancy and a range of infant clinical outcomes. Of particular interest was the extent to which any observed associations might reflect the direct causal effects of maternal methadone dose and/or the confounding effects of adverse maternal lifestyle factors correlated with methadone use during pregnancy. Findings revealed the presence of clear linear relationships between the mean methadone dose prescribed for mothers during pregnancy and a range of adverse infant clinical outcomes. With increasing maternal methadone dose there was a corresponding increase in infants' risk of being born preterm, being symmetrically smaller, spending longer periods in hospital and the need for treatment for Neonatal Abstinence Syndrome. After due allowance for potentially confounding maternal health and lifestyle factors, maternal methadone dose during pregnancy remained a significant predictor of preterm birth, growth, and the duration of infant hospitalization post delivery. These findings suggest a need to examine more closely the potential impacts of recent trends towards the use of higher methadone dose levels during pregnancy.