The Labour Progression Study, a Cluster Randomised Trial on Labour Progression for First Time Mothers

1. Introduction The increasing rate of emergency caesarean sections in developed countries is of great concern as it is associated with adverse outcomes for mother and infant. The rate of caesarean sections for first time mothers with a singleton foetus in a vertex position and spontaneous onset of labour at term has increased from 5.7 % to 9.2 % in Norway. The most common indication for emergency caesarean sections is Labour dystocia, even if there is no consensus on criteria for the diagnosis.

Labour dystocia is characterised by abnormally slow progress of labour and is among the most common challenges of birth care especially in first time mothers. When the labour progression is assessed to be prolonged according to current guidelines, labour dystocia is treated by amniotomy followed by oxytocin infusion to augment uterus contractions. Oxytocin is a potent drug and classified by the Institute for Safe Medication Practices in the USA as one of 12 medications which is "bearing heightened risk of harm".

In Norway the guidelines for expected progression of labour is based on modifications of Friedman's curve of cervical dilatation, a linear labour progression curve developed in 1953. Contemporary research by Zhang shows that the dilatation of the cervix can be substantially slower than earlier expected, especially at an early stage of labour.

Hypothesis: By adhering to the guideline for labour progression presented by Zhang, the rate of emergency caesarean sections in first time mothers will decrease compared to adhering to the guideline for labour progression based on a modified Friedman's curve, without jeopardising the maternal and neonatal outcomes. 2. Background and status of knowledge Traditionally the labour process is divided in two stages; the first stage and the second stage. The first stage is divided in two phases; the latent phase and the active phase, the latent phase is defined from onset of labour until the cervix is dilated four centimetres with 3-4 painful contractions per ten minutes. The active phase is defined from a cervix dilatation of four centimetres until fully dilated. The second stage is divided in two phases; the deceleration phase where the baby's head is decelerating towards the pelvic floor and the expulsion phase where the mother is actively pushing the baby out.

To visualize the progression of labour, the status of the cervix dilatation is traditionally measured and recorded throughout labour on a graphic curve often called a partogram. The partogram is widely used internationally and facilitates that midwives' and doctors' can monitor labour progression, and together with criteria for labour dystocia, consequently carry out necessary interventions.