Background It has been suggested that women who are regular exercisers have a tighter pelvic floor and thereby have more difficulty during childbirth than non-exercising women. We investigated whether women exercising before and during pregnancy have a narrower levator hiatus (LH) area than their sedentary counterparts. We also studied whether regular exercise at gestational week 37 influences delivery outcome.

Methods Cohort study of 274 nulliparous pregnant women assessed at mid-pregnancy and gestational week 37 by three-dimensional/four-dimensional transperineal ultrasonography of the LH area. Exercisers were defined as those exercising ≥30 min three times per week and non-exercisers as not exercising. Exercise data were collected via electronic questionnaire at mean gestational weeks 21 and 37. Labour and delivery outcomes were collected from the women's electronic medical birth records. Differences between exercisers and non-exercisers were analysed using independent sample t test or χ² test. p Value was set to ≤0.05.

Results At gestational week 37, exercisers had a significantly larger LH area than non-exercisers at rest and during PFM contraction (mean difference −1.6 cm² (95% CI −3.0 to −0.3), p=0.02 and −1.1 cm² (95% CI −2.0 to −0.1), p=0.04, respectively). No significant differences were found between exercisers and non-exercisers at week 37 in any labour or delivery outcomes.

Conclusions The results of the present study do not support the hypothesis that women exercising regularly before or during pregnancy have a narrower LH area or more complicated childbirths than non-exercising women.

Trial registration number ClinicalTrials.gov: NCT01045135.