Determination of fetal head position during labour is highly subjective and depends on clinician's experience in vaginal digital examination. Monitoring the progress of labour with intrapartum ultrasound (IU) exhibits higher accuracy rates. However, the dynamic process of labour needs very frequent sonographic examination and that may decrease the feasibility. Consultation to IU at certain time points can positively limit the need for ultrasound, increase the effectiveness of IU and allow for safer labour in consistency with traditional labour management. This study aims to investigate the use of IU in cases with suspected and diagnosed labour arrest in both the first and second stage of labour.

Low-risk pregnant women with singleton, vertex fetus who are at their 36th gestational weeks and above with suspected first and second stages of labour arrest will be enrolled in this study. Intrapartum ultrasound with transperineal and transabdominal approach will be performed at two specific time points; 1) Suspicion of labour arrest, 2) Diagnosis of labour arrest. The fetal head position, station, direction, progression and the structure of pubic arch will be evaluated with IU.

All ultrasound examinations will be monitored and recorded to the memory storage of ultrasound device. Recorded ultrasound examinations will be reviewed and measurements will be performed at the end of the study period by two experienced clinicians who are not involved in the examinations. These two blinded clinicians are not aware of labor outcomes, delivery types, maternal and neonatal outcomes.

General terms are defined according to the NICE guidelines. Those are; the first stage of labour is established when there are regular painful contractions and there is progressive cervical dilatation from 4 cm. If delay in the established first stage is suspected, all aspects of progress in labour are assessed when diagnosing delay, including; cervical dilatation of less than 2 cm in 4 hours for first labours, cervical dilatation of less than 2 cm in 4 hours, or a slowing in the progress of labour for second or subsequent labours, descent, and rotation of the baby's head, changes in the strength, duration and frequency of uterine contractions. Amniotomy is offered to a woman with suspected delay in the established first stage of labour and women are advised to have a vaginal examination 2 hours later, and diagnose delay if progress is less than 1 cm. If oxytocin is used due to insufficient uterine contractions delay is diagnosed as progress is less than 2 cm within 4 hours. With regard to the second stage of labour, for a nulliparous woman; birth would be expected to take place within 3 hours of the start of the active second stage in most women. The delay is diagnosed in the active second stage when it has lasted 2 hours and suspected delay if progress (in terms of rotation and/or descent of the presenting part) is inadequate after 1 hour of the active second stage. For a multiparous woman: birth would be expected to take place within 2 hours of the start of the active second stage in most women. The delay in the active second stage is diagnosed when it has lasted 1 hour for multiparous women and suspected delay if progress (in terms of rotation and/or descent of the presenting part) is inadequate after 30 minutes of the active second stage.

The International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) practical guidelines on intrapartum ultrasound recommend the evaluation of head position and descent during the active phase of labour when labor progress is slow and when operative delivery is considered. The use of IU is not meant to change the classic algorithm of labour monitoring but to provide objective and reliable evaluations of the traditional parameters of crucial importance when prolonged or arrested labour is suspected.

The aim of this study is to evaluate the use of IU in prolonged labour with optimizing the timing of IU.

Inclusion Criteria:

• Low-risk pregnant women at their 36th gestational weeks and above
• Singleton, vertex fetus births
• Patients in their active phase of labour in either the first or second phase of labour
• Cases with labour arrest suspicion

Exclusion Criteria:

• Breech presentation
• Multiple pregnancies
• Cases with fetal anomalies
• Intrauterine ex fetus cases
• Patients with vaginismus

Pregnant women whose active labour progress is prolonged

IPD will be shared upon request after scientific publication