OBJECTIVE: The purpose of this study was to determine the contribution of randomization to nicotine replacement therapy (NRT), sociodemographic and psychosocial factors, and pregnancy and medical history to serious perinatal adverse events among pregnant smokers. STUDY DESIGN: We performed a retrospective review of all medical records for participants in the Baby Steps Trial. Data that were abstracted from 157 records were combined with baseline characteristics for logistic regression modeling of serious adverse events and adjusted for covariates. RESULTS: Serious adverse events occurred in 17% (9/52 pregnancies) and 31% (33/105 pregnancies) of participants in the control and NRT arms, respectively. Black race, adverse pregnancy history, and use of analgesic medication during pregnancy were significant predictors (P = .02, .04, and .01, respectively). Remaining covariates, which included randomization to NRT, were not statistically significant. CONCLUSION: Although race, poor pregnancy history, and use of analgesics were associated with serious adverse events, randomization to NRT during pregnancy was not a significant factor. Further research is needed to examine the safety of analgesic medications during pregnancy.