Methadone and the causes of maternal and perinatal complications: a response to Pinto et al. 'Substance abuse during pregnancy: effect on pregnancy outcomes' [Eur. J. Obstet. Gynecol. Reprod. Biol. 150 (2010) 137-141]
Pinto et al.  are thanked for attempting to examine the complex relationships between drug use and maternal and perinatal outcomes. Their study, however, has several design flaws and the discussion contains a serious error of inference. These issues seriously limit the validity of their conclusions regarding the nature of the relationship between drug use and maternal and perinatal outcomes.