Objective: Describe safety and efficacy of a supervised, low-to-moderate intensity strength training program adopted during pregnancy among women at increased risk for back pain. Methods: 32 women adopted strength training twice per week for 12 weeks. Data on musculoskeletal injuries, symptoms, blood pressure, and the absolute external load used for 5 of 6 exercises were obtained during each session. A submaximal lumbar extension endurance exercise test was performed at weeks 5, 10, and 13. Results: The mean (± SD) exercise session attendance rate was 80.5% (± 11.3%). No musculoskeletal injuries occurred. Potentially adverse symptoms (eg, dizziness) were infrequent (2.1% of sessions). Repeated-measures ANOVA showed large increases in the external load across 12 weeks (all P values < .001) and the percentage increases in external load from weeks 1 to 12 were 36% for leg press, 39% for leg curl, 39% for lat pull down, 41% for lumbar extension and 56% for leg extension. Training was associated with a 14% increase in lumbar endurance. Blood pressure was unchanged following acute exercise sessions and after 12 weeks of exercise training. Conclusion: The adoption of a supervised, low-to-moderate intensity strength training program during pregnancy can be safe and efficacious for pregnant women. © 2011 Human Kinetics, Inc.