Abstract
OBJECTIVE: Activity restriction is commonly recommended in pregnancy despite lacking evidence of benefit. We sought to evaluate the amount of physical activity in patients at high risk for preterm birth and pregnancy latency and preterm birth. METHODS: This is an ancillary study of two randomized trials of preterm birth prevention in people with a short cervical length. People were enrolled from 16 0/7 to 23 6/7 weeks of gestation and instructed to wear a wrist accelerometer, which calculated physical activity data (steps per day) until delivery. The number of steps per day was calculated for each participant. The primary outcome was latency from time of enrollment to delivery. Sedentary activity was defined as a median of fewer than 3,500 steps per day. We compared outcomes between those with fewer than 3,500 median steps per day and those with 3,500 or more median steps per day. Secondary outcomes included preterm birth before 32, 34, and 37 weeks of gestation. RESULTS: Of the 120 participants enrolled in the ancillary study, 117 (97.5%) had complete accelerometer data. At enrollment, the median gestational age was 22.8 weeks (interquartile range 21.3, 23.7), and a quarter of participants (25.8%) had been placed on activity restriction by their practitioner. The primary outcome, latency from time of enrollment to delivery, was not different between the groups (hazard ratio 0.95, 95% CI, 0.88-1.03). Steps per day did not differ by median cervical length at baseline between the groups. However, participants with fewer than 3,500 median steps per day delivered at an earlier gestational age (34.9 weeks vs 37.7 weeks, P =.04) and were more likely to deliver before 34 weeks (47.3% vs 17.7%, P =.03). CONCLUSION: There was no statistically significant difference in latency from time of enrollment to delivery between those with and those without activity restriction. However, among individuals with a short cervix in the second trimester, sedentary activity (fewer than 3,500 steps per day) was associated with an increased risk of preterm birth before 34 weeks of gestation and delivery at an earlier gestational age.