This study aimed to evaluate postpartum maternal health and training outcomes of females who were competing or training as elite athletes before or during pregnancy. Methods: Online databases were searched up to August 26, 2020. Studies of any design and language were eligible if they contained information on the relevant population (postpartum athletes [any period after pregnancy]), exposure (engaged in the highest level of sport immediately before or during pregnancy), comparators (sedentary/active controls), and outcomes: maternal (breastfeeding initiation and duration, postpartum weight retention or loss, bone mineral density, low back or pelvic girdle pain, incontinence [prevalence or severity of stress, urge or mixed urinary incontinence, fecal incontinence], injury, anemia, diastasis recti, breast pain, depression, anxiety) and training (<6 wk time to resume activity, training volume or intensity, performance level). Results: Eleven studies (n = 482 females, including 372 elite athletes) were included. We identified "very low" certainty evidence demonstrating a higher rate of return to sport before 6 wk postpartum among elite athletes compared with nonelite athletes (n = 145, odds ratio = 6.93, 95% confidence interval = 2.73-17.63, I 2 = 11). "Very low" certainty evidence from three studies (n = 179) indicated 14 elite athletes obtained injuries postpartum (7 stress fractures, 9 "running injuries"). "Very low" certainty evidence from five studies (n = 262) reported that 101 (40.5%) elite athletes experienced improved performance postpartum. Conclusion: Compared with controls, "very low" quality evidence suggests that elite athletes return to physical activity early in the postpartum period and may have an increased risk of injury. Additional high-quality evidence is needed to safely guide return to sport of elite athletes in the postpartum period.

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In conjunction with significant cardiovascular adaptation, changes in cardioautonomic balance, specifically greater sympathetic activation and vagal withdrawal, are considered normal adaptations to healthy singleton pregnancy. Cardiovascular adaptation to twin pregnancy is more profound than that of singleton pregnancies; however, the changes in cardioautonomic control during multifetal gestation are unknown. To address this gap, beat-by-beat blood pressure (photoplethysmography) and heart rate (lead II electrocardiogram) were measured continuously in 25 twin pregnancies and 25 singleton pregnancies (matched for age, pre-pregnancy BMI and gestational age) during 10-minutes of rest. Data extracted from a 3- to 5-minute period was used to analyze heart rate variability (HRV), blood pressure variability (BPV), cardiovagal baroreflex gain and cardiac intervals as indicators of cardioautonomic control. Independent t-tests were used to determine statistical differences between groups (α=0.05) and the false rate discovery was determined to adjust for multiple comparisons. Resting heart rate was greater in twin compared to singleton pregnancies (91±10 vs. 81±10 bpm; P=0.001), but blood pressure was not different. Individuals with twin pregnancies had lower HRV, evidenced by lower standard deviation of R-R intervals (32±11 vs. 47±18 ms; P=0.001), total power (1035±810 vs. 1945±1570 ms2; P=0.004) and high frequency power (224±262 vs. 810±806 ms2; P<0.001) compared to singleton pregnancies. There were no differences in cardiac intervals, BPV and cardiovagal baroreflex gain between groups. Our findings suggest that individuals with twin pregnancies have greater sympathetic and lower parasympathetic contributions to heart rate and that cardiac, but not vascular, autonomic control is impacted during twin compared to singleton pregnancy.