The effect of pregnancy on hiatal dimensions and urethral mobility: an observational study

Childbirth is an established risk factor of pelvic floor dysfunction. The role of pregnancy is, however, not fully understood. This study was designed to evaluate the potential effect of pregnancy on pelvic floor function. The hypothesis was: Pregnancy has no effect on urethral mobility and levator hiatal dimensions.

This was a reanalysis of the translabial 3D/4D ultrasound volume data of 688 nulliparous pregnant women seen in the late 3rd trimester and again 4 months postpartum and that of 74 nulliparous, nonpregnant volunteers in previously reported studies. Hiatal dimensions and urethral mobility were determined as the outcome parameters. Multivariate regression analysis was performed after adjusting for age and BMI between the pregnant and nonpregnant cohorts.

Comparison of 3rd trimester data of the pregnant cohort with that of the nonpregnant nulliparae revealed a 27 % and 41 % increase in hiatal area at rest and on Valsalva and an increase in segmental urethral mobility by 64 % to 91 % in late pregnancy. About 70 % of this difference in hiatal dimensions, but virtually identical differences in urethral mobility, were observed when comparing nonpregnant controls with women 4 months after prelabour or 1st stage caesarean section.

Both hiatal dimensions and urethral mobility were markedly higher in women in late pregnancy and at 4 months after prelabour/1st stage caesarean section compared to nulliparous controls. The hormonal and mechanical changes of pregnancy may have an irreversible effect on the pelvic floor.