Mechanisms and management of normal labour

Normal labour is a complex process involving hormonal, biochemical and mechanical interdependence. There are four phases of parturition: quiescence, activation, stimulation and involution. These reflect the transition from the maintenance of myometrial acontractility and cervical structural integrity, to progressive uterine contractions, cervical effacement and dilatation, delivery of the fetus and placenta, and recovery to the non-pregnant state. Whilst parturition is chiefly controlled by the oestrogen:progesterone ratio, multiple hormones such as prostaglandins, corticotropin-releasing hormone, oxytocin and relaxin play a role in the initiation, maintenance and progression of normal labour. The mechanical challenge of labour is overcome when progressive, effective contractions occur in conjunction with satisfactory fetal and maternal pelvic dimensions. Clinically, there are three stages in the management of normal labour, reflecting cervical dilatation up to 4 cm, delivery of the fetus, and the placenta, respectively. Robust knowledge of the mechanisms and management of normal labour is key to our understanding of when to clinically intervene and recognize areas where maternal and fetal morbidity can be reduced.