Factors involved in changes in the levator ani during pregnancy.

Introduction and Hypothesis: Levator ani muscle (LAM) dimensions increase during pregnancy to allow the delivery of the fetus. The objective was to investigate which factors are involved in LAM modifications during pregnancy.
Methods: A prospective longitudinal observational study was conducted between July 2015 and March 2018. Ninety-nine nulliparous pregnant women were included. Data on the physical examination, 4D transperineal ultrasound and hormonal concentrations (progesterone, oestradiol and relaxin) were collected during the first and third trimesters.
Results: We found higher hiatal dimensions at the beginning of pregnancy than in other studies with nonpregnant women. Increases in the levator ani hiatal (LH) dimensions were observed at contraction (1.01 ±1.96 cm ² ), rest (0.82 ± 2.51 cm ² ) and on Valsalva (2.36 ± 3.64 cm ² ) throughout pregnancy. The distensibility in the third trimester was higher than in the first trimester (5.79 vs 4.24 cm ² ; p=0); however, the contractility was lower (-3.32 vs -3.5 cm ² ; p=0.04). Women with lower scores on the Modified Oxford Grading Scale in the third trimester presented with lower contractility in the LAM. A larger LH at the end of pregnancy was associated with age and body mass index. Eleven women developed ballooning during pregnancy; in these women, relaxin was higher in both trimesters than in women without ballooning, but these results were not statistically significant. The linear models to predict third-trimester Valsalva LH, distensibility and contractility were not conclusive and did not show any factors to predict LAM modifications during pregnancy.
Conclusions: Hormones could play a role in modifying the muscle properties of LAM from the beginning of pregnancy, but we did not find an association between LAM measurements and hormone concentration in this study.
(© 2023. The International Urogynecological Association.)