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Introduction to mechanisms of normal labour and delivery

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Labour is defined as the onset of regular uterine activity associated with effacement and dilatation of the cervix and descent of the presenting part through the cervix. The control and timing of delivery is crucial in the survival of any species and, in most, the interval between conception and parturition varies little.

This is not the case in human pregnancy, where delivery can occur many weeks before or after the expected date. It is recognised that intervention by induction of labour in prolonged pregnancies reduces the likelihood of perinatal mortality, (see the StratOG tutorial on Induction of labour and prolonged prgnancy); however, the biggest single cause of perinatal and neonatal death in the developed world is preterm delivery (see the StratOG tutorial on Preterm labour).

At present, the factors maintaining myometrial quiescence during pregnancy and those that stimulate the onset of uterine contractions and cervical ripening remain obscure.

Learning objectives

The aims of this module are to review:

  • the anatomy of the fetal skull and female pelvis, relevant to labour
  • changes in the uterus during pregnancy
  • the factors involved in the onset of labour
  • the initiation of human labour – molecular mechanisms
  • the mechanism of normal labour and delivery
  • monitoring progress in labour

The assessment of fetal wellbeing in labour, pain relief in labour and perineal trauma are discussed in other StratOG tutorials.

Last updated: 25/08/10 (two animations of placental delivery showing physiological labour and controlled cord traction were added to the Animations of placental delivery section)

28/06/10 (tutorial reviewed and updated by Dr Andrew Thomson and Dr Claire Banks)

26/01/10 (image on cervical ripening page replaced with a new, higher quality version)

28/01/09 (BJOG article added in the Preliminary reading section)

17/10/08 (latest RCOG patient information on VBAC added in Preliminary reading).

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