Third Stage of Labour

The third stage of labour refers to the period from delivery of the baby to the delivery of the
placenta. The placenta separates as a result of shearing force between the placental surface
and the uterine wall in the presence of uterine muscular contraction. The major complication is post-partum haemorrhage. PPH is the most common cause of maternal death. The degree of blood loss associated with placental separation and delivery depends on the efficiency of uterine muscle contraction and the time taken to expel the placenta from the uterus. The length of the third stage of labour is usually 5-15 minutes.

Physiology of the third stage of labour
Placenta is an organ attached to the uterine wall throughout the pregnancy. It connects the developing foetus with uterine wall and supplies nutrients and oxygen to the foetus from the maternal blood. The placenta is expelled shortly after the delivery of the baby.

Placental separation occurs due to the shearing placental surface with uterine contractions after the delivery of the baby. Gus of blood, lengthening of the umbilical cord and anterior cephalad movement of the uterus are considered the signs of placental separation. The fundus becomes firmer and globular. Placental explusion occurs due to a combination of events including spontaneous uterine contractions, downward pressure from the developing retro-placental haematoma and increase in intra-abdominal pressure. These changes in the uteroplacental region are divided into four phases: latent, contraction, detachment and expulsion phase.1

Latent phase determines the duration of the third stage of labour. It is characterised by beginning of periodic myometrial contractions. These contractions at the placental site continue throughout the contraction phase.1 Thickening of the placenta-site wall occurs towards the end of the latent phase which causes cessation of the basal blood flow between the placenta and myometrium, thus preventing...