Mechanisms and management of normal labour

Normal labour reflects the culmination of several complex and complimentary processes, relying on hormonal, biochemical and mechanical interdependence. The four phases of parturition (quiescence, activation, stimulation and involution) in short reflect the transition from gestation to initiation and propagation of labour, delivery of the fetus and placenta, and recovery to the non-pregnant state. Appropriate physiological regulation of this process is key to achieving maturity for the neonate and prevention of associated maternal and neonatal morbidity. Myometrial acontractility and cervical structural integrity are maintained throughout gestation chiefly by progesterone. As gestation advances, functional withdrawal of progesterone, as well as other hormonal influences, mechanical stretch and a cascade of inflammatory processes stimulate the initiation and propagation of labour. Mechanically, labour may only progress when effective uterine contractions occur in conjunction with satisfactory fetal and maternal pelvic dimensions. The three clinical stages of labour reflect regular uterine activity and cervical dilatation up to four centimetres, delivery of the fetus, and the placenta, respectively. Labour represents a challenge for both birthing person and fetus, therefore robust knowledge of normal processes and physiological responses is essential to our understanding of how to appropriately care for and monitor those in labour, and to recognize when clinical intervention is indicated, such that maternal and fetal morbidity may be reduced.