Parturition, or childbirth, is the process by which the fetus and placenta are expelled from the uterus at the end of pregnancy.
It involves a series of complex physiological events and is typically divided into three stages: the first stage (latent and active phases of labour), the second stage (delivery of the baby), and the third stage (delivery of the placenta).
Mechanism of Parturition
I. Hormonal Factors:
The onset of labor is believed to be triggered by an interplay of hormones, including increased levels of estrogen, prostaglandins, and oxytocin.
These hormones stimulate uterine contractions, soften the cervix (the lower part of the uterus opening into the vagina), and promote the release of more oxytocin, creating a positive feedback loop that intensifies contractions.
II. Mechanical Factors:
The growing fetus and its movement within the uterine cavity exert mechanical pressure on the cervix and uterine wall.
This pressure is thought to contribute to the initiation of labor.
Stages of Parturition
1. First Stage of Labor: Cervical Dilation and Effacement
I. Latent Phase:
This initial phase is characterized by the softening, shortening (effacement), and opening (dilation) of the cervix, facilitated by irregular and mild to moderate uterine contractions.
For first-time mothers, this phase can last from several hours to a few days.
II. Active Phase:
Following the latent phase, the active phase sees regular, strong contractions and more rapid dilation of the cervix, moving from 4 cm to 10 cm.
This phase is marked by increased pain and pressure, lasting several hours.
2. Second Stage of Labor: Delivery of the Baby
I. Pushing:
With the cervix fully dilated to 10 cm, the mother is encouraged to push with each contraction, aiding the baby's descent through the birth canal.
The emergence of the baby's head, known as "crowning," signals the imminent birth.
II. Delivery:
The final pushes result in the birth of the baby.
The healthcare provider assists by guiding the baby out and ensuring the umbilical cord is safely clamped and cut.
3. Third Stage of Labor: Delivery of the Placenta
This stage involves the delivery of the placenta, which follows the birth of the baby.
I. Separation and Expulsion:
After the baby is born, uterine contractions continue, leading to the separation of the placenta from the uterine wall.
The mother may be asked to push gently to facilitate the expulsion of the placenta, typically occurring within 5 to 30 minutes post-delivery.
II. Examination:
The healthcare provider examines the delivered placenta to ensure it is complete, with no fragments left behind in the uterus.
Retained placenta fragments could lead to postpartum complications, so careful examination is crucial.