The association between vaginal parity and hiatal dimensions: a retrospective observational study in a tertiary urogynaecological centre

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Abstract
Objective: Vaginal childbirth has a substantial effect on pelvic organ supports, which may be mediated by levator ani (LA) avulsion or hiatal overdistension. Although the impact of a first vaginal delivery on the hiatus has been investigated, little is known about the effect of subsequent births. This study was designed to evaluate the association between vaginal parity and hiatal dimension.Design: Retrospective observational study.Setting: A tertiary urogynaecological unit in Australia.Population: A total of 780 archived data sets of women seen for symptoms of lower urinary tract and pelvic floor dysfunction.Methods: Standardised in‐house interview and assessment using the International Continence Society (ICS) pelvic organ prolapse quantification (POP‐Q), and four‐dimensional translabial ultrasound. Offline analysis for hiatal dimensions was undertaken blinded to history and clinical examination.Main outcome measures: Hiatal area on maximum Valsalva.Results: Of 780 women, 64 were excluded because of missing ultrasound volumes, leaving 716 for analysis: 96% (n = 686) were parous, with a median parity of three (interquartile range, IQR 2–3), and 91.2% (n = 653) were vaginally parous. Levator avulsion was found in 21% (n = 148). The mean hiatal area on Valsalva was 29 cm2 (SD 9.4 cm2). On one‐way anova, vaginal parity was significantly associated with hiatal area (P < 0.001). Most of the effect seems to occur with the first delivery. Subsequent deliveries do not seem to have any significant effect on hiatal dimensions. This remained true after controlling for potential confounding factors using multivariate regression analysis (P = 0.0123).Conclusions: Vaginal parity was strongly associated with hiatal area on Valsalva. Most of this effect seems to be associated with the first vaginal delivery.

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