Trimester-specific association of maternal prenatal physical activities with risk of preterm birth: a prospective pre-birth cohort study

This study aimed to examine the trimester-specific association of maternal prenatal physical activities (PA) with risk of preterm birth (PTB). We recruited 2080 women during the first trimester and conducted follow-ups during the second and third trimesters and at birth. We assessed maternal PA during each trimester and calculated a cumulative PA score range from 0 to 3, with a higher score reflecting higher frequency and a sustained high level of PA over pregnancy. Lower risks of PTB were observed among women who had higher PA levels during the first [tertile 3 (T3) vs. tertile 1 (T1): odds ratio (OR) = 0.48; 95% confidence interval (CI): 0.32–0.71, P for trend = 0.003], second (T3 vs. T1: OR = 0.34; 95% CI: 0.22–0.52, P for trend < 0.001), and third trimesters (T3 vs. T1: OR = 0.28; 95% CI: 0.18–0.45, P for trend = 0.008), respectively. A higher prenatal cumulative PA score significantly correlated with a lower risk of PTB (3 vs. 0: OR = 0.24; 95% CI: 0.11–0.54, P for trend < 0.001) and iatrogenic preterm birth (3 vs. 0: OR = 0.23; 95% CI: 0.09–0.59, P for trend < 0.001) in a dose–response-dependent manner, but not with spontaneous preterm birth. These findings support the necessity of guiding the maternal PA from early pregnancy and highlight the importance of sustained PA to prevent PTB.