Assessing the impact of twin pregnancies on the pelvic floor using 3-dimensional sonography: a pilot study

The purpose of this study was to compare the morphologic characteristics of the pelvic floor musculature between women with twin and singleton pregnancies. We conducted a cross-sectional case-control study of 40 nulliparous women aged 20 to 38 years to compare women with singleton pregnancies (n = 23) to women with twin pregnancies (n = 17). Biometric measurements of the levator hiatus and the sagittal and coronal diameters were made by transperineal 3-dimensional sonography between the 28th and 38th gestational weeks. Comparisons were statistically assessed by the unpaired Student t test and Mann-Whitney U test. For the women with singleton pregnancies, the mean sagittal diameters at rest, during the Valsalva maneuver, and during pelvic floor contraction were 5.3, 5.7, and 4.5 cm, respectively, and the mean coronal diameters under these conditions were 3.8, 4.1, and 3.6 cm. For the women with twin pregnancies, the corresponding values were as follows: mean sagittal diameters, 5.3, 5.8, and 4.6 cm; and mean coronal diameters, 4.3, 4.3, and 3.8 cm. The differences in coronal diameters were statistically significant at rest (P < .01) and during contraction (P = .04). The mean levator hiatal areas for the women with singleton pregnancies were 14.6, 16.9, and 11.7 cm(2) at rest, during Valsalva, and during contraction, respectively; for the women with twin pregnancies, these values were 16.0, 18.6, and 12.6 cm(2). Hiatal measurements were higher in twin than in singleton pregnancies, with coronal diameters reaching significance at rest and during contraction, suggesting that pelvic support undergoes greater changes during twin pregnancy.