Objectives: This study investigated whether, in a general obstetric population, exercise in pregnancy affects the timeliness of delivery. The hypothesis was that maternal exercise would not raise the risk of preterm birth.
Methods: A community cohort of 557 prenatal patients was followed up until the time of delivery. Data were collected on exercise in each trimester: none, low-moderate (< 1000 kcal [4184 kJ]/wk in energy expenditure), or heavy (> or = 1000 kcal/wk). Timely delivery was adopted as an outcome criterion. Thus, in the analysis, a term birth was treated as optimal and survival techniques were used to estimate risks for both preterm and postdates delivery.
Results: No association was found between low-moderate exercise and gestational length. Heavier exercise appeared to reduce, rather than raise, the risk of preterm birth. The adjusted relative risk among conditioned heavy exercisers was 0.11 (95% confidence interval = 0.02, 0.81). After term, conditioned heavy exercisers delivered faster than nonexercisers.
Conclusions: The most important finding was the lack of evidence that vigorous maternal exercise is a risk factor for preterm delivery. A promising finding was that conditioned heavy exercisers have timely deliveries.