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.
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
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
Consecutive women with a singleton cephalic pregnancy at 36 weeks of gestation or more admitted to the induction of labour service of a tertiary maternity unit, with the intention of vaginal birth, who consent to research pelvic floor ultrasound before the start of cervical ripening.
Cohort
Prospective
Three-dimensional transperineal pelvic floor ultrasound
Diagnostic testTransperineal acquisition of 3D/4D pelvic floor volumes at rest, on maximum pelvic floor contraction and on maximum Valsalva manoeuvre, using a transabdominal volumetric probe applied translabially with the woman in the lithotomy position and an empty bladder. Levator hiatal area and diameters are measured offline on the plane of minimal hiatal dimensions using automated segmentation software, with manual tracing as a quality control. No vaginal or rectal probe is used and no ionising radiation is involved. - Other names: TPUS; pelvic floor ultrasound
Duration of the active (pushing) second stage of labour
Time elapsed from the onset of active maternal pushing to delivery of the fetus, recorded in minutes from the clinical record, analysed in relation to the levator hiatal area measured on maximum Valsalva before induction
Duration of the active phase of the first stage of labour
Duration of the active phase of the first stage of labour - Description: Time in minutes from the first documented cervical dilatation of 5 cm or more with regular contractions to confirmed full cervical dilatation.
Duration of the passive second stage of labour
Time in minutes from the first documented cervical dilatation of 5 cm or more with regular contractions to confirmed full cervical dilatation.
Induction-to-delivery interval
Time in minutes from the administration of the first cervical ripening agent to delivery.
Mode of delivery a
Proportion of participants delivering by spontaneous vaginal birth, operative vaginal birth (vacuum or forceps) and intrapartum caesarean section, with the recorded indication
Intra- and interobserver reproducibility of automated levator hiatal area measurement
Intraclass correlation coefficient for repeated automated measurements of levator hiatal area by the same operator and by two independent operators, in the first 30 participants. -
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