Previous research by this group has found that methadone treatment during pregnancy directly impacts fetal neurophysiology independently of maternal physiology. Buprenorphine is a new therapy for opiate dependent individuals, and its use during pregnancy is currently being evaluated. Some research has shown that buprenorphine lessens the neonatal abstinence syndrome when compared to methadone. Thirty methadone and 30 buprenorphine maintained women will be evaluated at 24, 28, 32 and 36 weeks gestation using a state-of-the-art computerized fetal actocardiograph and data analysis program to simultaneously evaluate fetal movement and heart rate and maternal physiologic parameters. Investigators will be blinded to treatment group. Longitudinal neurodevelopment of the fetuses in each group will be explored. The differential effects of methadone and buprenorphine on the neonatal abstinence syndrome will also be explored.