The purpose of this study is to evaluate the effects of drugs used by treatment providers on the fetuses and infants of opiate dependent women. The subjects in this study are women enrolled in a large, multi-site, double blind study that looks at the effects of methadone and buprenorphine treatment during pregnancy. This study will evaluate fetal and maternal biophysiologic data longitudinally during pregnancy to determine how these substances may affect fetal neurobehavior. Additionally, infant neurobehavioral assessments and measurements of infant vagal tone will be collected to see how methadone and buprenorphine differentially affect the neonatal abstinence syndrome, or "withdrawal" in exposed neonates.