Table 1.

Covariates considered as potential confounders in 5 of 16 identified studies of the comparative safety of prenatal buprenorphine vs. methadone exposure on the neonate.

Study	Participants	Location	Years of Birth	Covariates
Kakko, et al. [15]	Prospective (2001–2006) and retrospective (1982–2006) cohort of 83 mother-neonate pairs at an antenatal clinic	Stockholm, Sweden	2001 to 2006 buprenorphine exposed, 1982 to 2006 methadone exposed	Maternal age
Jones, et al. [7]	Randomized controlled trial of 175 mother- neonate pairs	Six sites in the US, Canada and Austria	2005 to 2008	Number of days of buprenorphine or methadone exposure, cigarette use at enrollment, selective serotonin reuptake inhibitor use at enrollment, percent of urine tests positive for cocaine in pregnancy, number of prenatal visits at enrollment, gestational age at delivery
Lacroix, et al. [10]	Prospective multisite cohort of 135 mother-neonate pairs (125 resulted in live births)	France	1998 to 2006	Heroin use late in pregnancy
Welle Strand, et al. [11]	Cohort of 139 mother-neonate pairs in opioid maintenance treatment	Norway	1996 to 2009	Maternal age, years of opioid dependence before treatment, dose of buprenorphine or methadone at delivery, other drug use (opiates, benzodiazepines, amphetamines, cannabis) one month before pregnancy confirmation, cigarette use and other drug use one month before delivery
Wiegand, et al. [25]	Retrospective cohort of 62 mother-neonate pairs	Chapel Hill, North Carolina, US	2001 to 2013	Gestational age at birth, maternal indication for opioids