Three-dimensional ultrasound imaging of the levator hiatus in late pregnancy and associations with delivery outcomes

Objective: To determine the correlations between dimensions of the levator hiatus in late pregnant nulliparous women, mode of delivery and length of second stage. Methods: This was a prospective observational pilot study of 61 nulliparous women seen and examined between 36 and 40 weeks of pregnancy. A translabial ultrasound examination was undertaken, and three-dimensional volumes comprising the levator hiatus were recorded at rest, during a pelvic floor muscle contraction and on Valsalva. The volumes were analysed in a blinded fashion using proprietary software to determine linear dimensions and hiatal area. Information regarding delivery outcomes and course of labour was obtained from the obstetric database. Statistical analysis was undertaken for correlations between hiatal dimensions and labour outcomes. Results: No consistent correlations were found between levator dimensions and delivery mode. However, an inverse correlation was demonstrated between the area of the hiatus, particularly on pelvic floor contraction, and length of total second stage. Conclusions: Levator hiatal dimensions are associated with the length of the second stage of labour. Although the numbers were small, our findings suggest that the effect of pelvic floor structures on progress in labour is worth further study.