Background: The Valsalva maneuver may increase maternal blood pressure and intra-abdominal pressure, resulting in decreased blood flow to the fetus during resistance training. Hypothesis: There is no significant reduction in placental blood flow in pregnancy during resistance training in recreational athletes, as documented by a 3-dimensional power flow Doppler ultrasonography. Study Design: Cohort. Level of Evidence: Level 3. Methods: A cohort of healthy women who participated in recreational athletics was enrolled in a prospective study to assess placental blood flow during a resistance exercise. A 1 repetition maximum (1RM, up to 50 lb) was determined through a modified chest press as a marker of heavy resistance training. Three-dimensional volume measurements and power Doppler flow were determined at the rest phase and during the 1RM lift phase. The vascular flow index (VFI) was calculated to determine placental perfusion during each phase. Results: A total of 22 women participated. The mean age of participants was 31 years. Gestational age ranged from 13 to 28 weeks. Average 1RM weight lifted was 30 lb. Four women (18%) were able to lift 50 lb, the maximum weight that the study allowed. The remaining 18 women (82%) lifted their true 1RM. Mean VFI during lift phase was 2.185 compared with 2.071 at rest (P = 0.03). There was a slight mean increase in VFI during lift phase, 0.114 (95% CI 0.009-0.182) from 2.071 to 2.185 with lifting (P = 0.03). The 15 women who participated in structured exercise had a mean VFI at rest and during the lift phase of 2.031 and 2.203, respectively (P = 0.01). Conclusion: Three-dimensional power flow Doppler imaging can guide resistance training during pregnancy to prevent fetal injury due to hypoperfusion. Resistance training up to an RM1 of 50 lb did not result in a significant reduction of placental blood flow from resting state in the study population. Clinical Relevance: This technique may be used to guide training parameters among pregnant athletes.