Pelvic Floor Ultrasound Before Induction of Labour and Labour Outcome

Pregnancy and vaginal birth are the main causes of pelvic floor disorders such as urinary incontinence and pelvic organ prolapse. The levator hiatus - the opening in the pelvic floor muscles through which the baby passes - can be measured on three-dimensional transperineal ultrasound at rest, during pelvic floor contraction and during a Valsalva manoeuvre. Its size and its ability to stretch have been related to how long labour lasts and to how the baby is eventually born, but the evidence comes mostly from women in spontaneous labour, in whom the exact time labour began cannot be established. Women having their labour induced offer a better model, because the time each stage of labour begins is documented. Recently, automated software has made the measurement of the levator hiatus fast and reproducible, which makes it realistic to use in everyday practice. This prospective observational study will enrol 140 women with a singleton pregnancy at 36 weeks or more who are scheduled for induction of labour. Before induction begins, each woman will have a transperineal ultrasound scan of the pelvic floor at rest, on maximum contraction and on maximum Valsalva. The scan does not involve any vaginal probe, radiation or injection, and takes about 15 minutes. The times of each phase of labour, the way the baby is born and the condition of the perineum after birth will be recorded prospectively from the clinical record. The scan will be repeated before hospital discharge and about one month after birth, together with validated pelvic floor symptom questionnaires. The main question is whether the area of the levator hiatus measured on Valsalva before induction is related to the duration of the active, pushing phase of the second stage of labour. The study will also examine the duration of the first stage, the mode of delivery, and how the pelvic floor changes in the first month after an induced birth. Study procedures do not influence clinical care in any way: induction and labour are managed according to standard departmental protocols, and the research ultrasound results are not disclosed to the clinical team.

Inclusion Criteria - * Age 18 years or older * Singleton pregnancy with cephalic presentation * Gestational age of 36 weeks 0 days or more, dated by first-trimester crown-rump length * Scheduled for induction of labour with a planned attempt at vaginal delivery, for any clinical indication * Ultrasound assessment feasible before administration of the first cervical ripening agent * Written informed consent Exclusion Criteria - Multiple pregnancy or non-cephalic presentation * Known fetal structural or chromosomal anomaly * Previous caesarean section or previous uterine surgery * Planned caesarean section or a contraindication to vaginal delivery arising before the ultrasound assessment * Connective tissue disease, neuropathy or neuromuscular disease affecting the pelvic floor * Previous pelvic floor or anti-incontinence surgery - Active labour, or ruptured membranes with regular contractions, at the time of the scheduled assessment * Inability to perform an adequate Valsalva manoeuvre or pelvic floor contraction after standardised instruction * Inability to provide informed consent or to understand the study questionnaires