The umbilical cord and the placenta form a temporary organ system that sustains a developing fetus throughout pregnancy. This complex structure facilitates the transfer of oxygen and nutrients from the mother’s bloodstream while removing waste products and carbon dioxide. Once the baby is born, this temporary organ has completed its function. The mother’s body then begins a physiological process to expel the system and heal the site of attachment.
The Third Stage of Labor
The process of expelling the temporary organ system is the third stage of labor, beginning immediately after delivery. The uterus continues to contract, causing the placenta to detach from the uterine wall. The placenta, often referred to as the “afterbirth,” is then delivered through the birth canal.
Management of this stage can be expectant or active. Expectant management allows the placenta to be expelled naturally without medical intervention, relying on the body’s own contractions. Active management involves administering a uterotonic medication, such as oxytocin, to stimulate strong uterine contractions. This speeds up delivery and helps minimize blood loss.
The final expulsion signals the end of this stage. Medical staff typically examine the entire structure, including the cord, to ensure it is complete and that no fragments have been left behind in the uterus.
The Placental Attachment Site
Once the placenta separates from the uterine wall, it leaves a large, open wound inside the uterus. This site is rich with numerous large blood vessels that previously supplied the placenta. The body’s immediate response to prevent excessive bleeding is a mechanical process known as hemostasis.
The uterine muscles (myometrium) contract vigorously after delivery, rapidly shrinking the uterus. This contraction acts like a natural tourniquet, compressing the severed blood vessels within the muscle tissue. These compressed muscle fibers are sometimes called “living ligatures” because they mechanically clamp down on the vessels to stop blood flow.
A failure of the uterus to contract strongly, known as uterine atony, is the most common cause of significant postpartum hemorrhage. The uterus must maintain this firm, contracted state until the blood vessels are sealed off through clotting. This mechanism is an immediate action to manage the wound left by the departed organ.
Postpartum Healing and Uterine Involution
Following the placenta’s expulsion, the uterus begins a weeks-long process of returning to its non-pregnant state and size, called uterine involution. The uterus shrinks significantly, decreasing from approximately 1,000 grams immediately after birth to around 60 to 100 grams by six to eight weeks postpartum.
This process involves the shedding of the superficial layer of the uterine lining, resulting in a vaginal discharge known as lochia. Lochia is composed of blood, tissue fragments, and mucus, reflecting the healing of the placental attachment site and the regeneration of the endometrium.
Lochia follows a typical progression:
- Lochia rubra: A dark or bright red discharge lasting three to four days.
- Lochia serosa: A pinkish-brown, watery discharge that lasts about a week.
- Lochia alba: A creamy, yellowish-white discharge that can continue for several weeks until healing is complete.
The hormone oxytocin, which is released during breastfeeding, stimulates uterine contractions. This can help accelerate the process of involution and the clearing of lochia. Overall, the recovery of the internal wound and the reduction of the uterus back to its pre-pregnancy size typically takes around six weeks.