Objectives

1. To assess if head-perineum distance and angle of progression measured with transperineal ultrasound by the obstetrician on call can predict delivery mode in primiparous women with prolonged first stage of labour.
2. To compare ultrasound assessments and clinical examinations.

Variables Digitally assessed cervical dilatation, fetal station and position Ultrasound measured fetal head-perineum distance. Ultrasound measured angle of progression Ultrasound assessed position

Possible confounders Ethnicity, maternal age, gestational age, BMI, induction of labour, augmentation, epidural analgesia, birth weight, head circumference

A two-dimensional ultrasound measurement will be obtained with the ultrasound device available in the delivery department. Fetal head descent is measured as the shortest distance between the outer bony limit of the fetal skull and the perineum with a curved transabdominal transducer placed transperineally between the labia in a transverse view (1).

The fetal descent will also be assessed measuring "angle of progression" as suggested by Barbera et al. The ultrasound transducer will be placed on the perineum in a mid-sagittal position between the labia below the pubic symphysis. The angle between a line through the symphysis and a line from the posterior part of the symphysis tangentially to the fetal skull contour will be measured (2)

A transabdominal scan will also be performed determining the fetal position as described previously. Positions ≥ 02.30 and ≤ 03.30 hours should be recorded as left occiput transverse and positions ≥ 08.30 and ≤ 09.30 as right occiput transverse. Positions > 03.30 and <08.30 should be recorded as occiput posterior and positions > 09.30 and < 02.30 as occiput anterior.(3).

Inclusion Criteria:

• Primiparous women with single pregnancies and gestation age > 37 weeks and prolonged first stage of labor

Exclusion Criteria:

• High risk pregnancies,
• premature deliveries,
• multiple pregnancies

primiparous women in labor

Postpartum period