parturition

Parturition, or birth, is the process by which a fetus is delivered from the uterus. It ends gestation and initiates the postpartum period in mammals, including humans. Labor can occur spontaneously or be medically induced, and deliveries may be vaginal or by cesarean section.

In humans, labor is described in three stages. Stage I involves cervical dilation and effacement as uterine contractions begin; it is sometimes subdivided into a latent phase and an active phase. Stage II begins with full dilation and ends with birth of the baby, driven by pushing. Stage III follows birth and ends with delivery of the placenta.

Labor is driven by hormonal and mechanical signals. Placental hormones and fetal signals promote cervical ripening and prostaglandin production. Oxytocin released from the posterior pituitary stimulates uterine contractions, which are reinforced by prostaglandins and other mediators. Rupture of the membranes may occur before or during labor.

Management of parturition varies. Many labors progress without intervention; others are induced to facilitate delivery. Medical efforts may include careful monitoring, analgesia or anesthesia, and, if needed, augmentation with oxytocin or cesarean delivery for safety.

Common complications include dystocia, fetal distress, placental problems, and postpartum hemorrhage. Premature or post-term pregnancies carry additional risks. Most births occur without major incident with appropriate medical care.