Abstract
OBJECTIVE: To estimate the association between physical activity and risk of subclinical and clinical pregnancy loss among women with a history of pregnancy loss. DESIGN: Prospective cohort study as a secondary analysis of the Effects of Aspirin in Gestation and Reproduction randomized controlled trial of preconception-initiated low-dose aspirin among women with one or two prior pregnancy losses. SETTING: Four U.S. clinical centers, 2007-2011. PATIENT(S): Women with confirmed pregnancy (n = 785) as determined from hCG testing in longitudinally collected biospecimens. MAIN OUTCOME MEASURE(S): Subclinical loss of pregnancy detected only by hCG testing and clinically recognized loss. RESULT(S): Among 785 women (mean [SD] age, 28.7 [4.6] years) with an hCG-confirmed pregnancy, 188 (23.9%) experienced pregnancy loss. In multivariable models adjusted for confounders, compared with the first tertile of physical activity (median = 7.7 metabolic equivalent of task hours/week), there was a roughly twofold higher risk of subclinical loss in the second (risk ratio = 2.06; 95% confidence interval, 1.03-4.14) and third tertiles (risk ratio = 1.92; 95% confidence interval, 0.94-3.90), with median metabolic equivalent of task hours/week of 27.8 and 95.7, respectively. No relations were observed between physical activity and clinically recognized loss. CONCLUSION(S): Risk related to physical activity is different for pregnancy failure close to the time of implantation compared with that for later, clinical pregnancy loss. Higher physical activity levels were associated with an elevated risk of subclinical loss (i.e., pregnancies detected only by hCG, n = 55); however, no relationship was observed with clinically recognized loss. Further work is required to confirm these findings, assess generalizability to women without prior losses, and evaluate mechanisms. ETHICAL APPROVAL: Each participating center's Institutional Review Board approved the study, and participants provided written informed consent. The trial was registered on ClinicalTrials.gov (NCT00467363), and a Data Safety and Monitoring Board provided oversight.