Uterine artery and umbilical vein blood flow are unaffected by moderate habitual physical activity during pregnancy

OBJECTIVE: This study aims to noninvasively quantify blood flow in the uterine arteries (UTAs) and umbilical vein (UV) using phase-contrast magnetic resonance imaging (PC-MRI) and test whether these correlate with maternal fitness parameters. METHOD: Resting UTA and UV flows were measured in 23 healthy 30 ± 3-year-old women who engaged in moderate-intensity physical activity during pregnancy. Participant fitness was characterized in the second and third trimesters using the submaximal oxygen uptake (VO₂ ) test measuring heart rate (HR), VO₂ , ventilation (ventilatory equivalent [VE]/VO₂ ), and the Borg rating of perceived exertion (respiratory quotient [RQ]). Linear regression models were used to determine the associations between blood flow and maternal fitness measures. RESULTS: Blood flows in the UTA (957 ± 241 mL/min) and UV (132 ± 38 mL/min/kg) were successfully measured in 20 (87%) participants. Neither was associated with any physical fitness parameters (HR, VO₂ , VE/VO₂ , and RQ) nor with any second-to-third trimester change in these parameters. CONCLUSION: PC-MRI can be used to noninvasively measure blood flow in the UTA and UV. Neither resting UTA nor UV flow is associated with maternal fitness parameters. This is the first MRI-based study to provide novel hemodynamic data suggesting decoupling between maternal moderate fitness level and the maternal-placental-fetal hemodynamic system in healthy, normal body mass index (BMI) pregnancies.