The placenta is an organ developed during pregnancy that acts as a temporary life support system, facilitating the exchange of nutrients, oxygen, and waste between the mother and the developing fetus. Immediately after the baby is born, the delivery process enters its final phase, known as the third stage of labor. This stage concludes only when the placenta is completely expelled from the uterus.
The Physiology of Placental Separation
The process of placental separation is driven by the uterus continuing to contract, though these contractions are less intense than those experienced during the birth. Once the uterus is emptied, its muscular wall rapidly shrinks, significantly reducing the surface area where the placenta was attached. This reduction causes a shearing force between the uterine wall and the relatively inelastic placenta.
This mechanical stress causes the placenta to peel away from the uterine lining. As separation occurs, blood vessels rupture, leading to a small collection of blood that aids in the final detachment. This process usually takes place within five to thirty minutes. Providers monitor for signs of full detachment, including a sudden gush of blood, a lengthening of the umbilical cord, and the uterus becoming firmer.
Active Versus Expectant Management
The two primary ways providers manage the third stage of labor are expectant management and active management. Expectant management, often preferred in low-risk settings, relies on the body’s physiological signals to complete the process without intervention. The provider waits for natural signs of separation and encourages maternal efforts, such as gentle pushing, to expel the placenta.
Active management involves timed interventions intended to speed up delivery and reduce the risk of excessive bleeding. This is the standard of care in most hospital settings due to its proven efficacy in reducing postpartum hemorrhage. Active management consists of three main components:
- Administering a uterotonic medication, typically synthetic oxytocin, immediately after the baby is born.
- Applying controlled cord traction (CCT).
- Performing uterine massage.
Administering oxytocin causes the uterine muscle to contract strongly, accelerating separation and constricting the blood vessels at the placental site. The provider then applies controlled traction to the umbilical cord while simultaneously applying counter-pressure on the abdomen to guide the placenta out.
After the placenta is expelled, the provider performs a fundal massage, rubbing the top of the uterus through the abdomen. This encourages continued, firm contraction, which acts as a natural clamp on the open blood vessels.
Immediate Post-Delivery Examination
Once the placenta is delivered, it undergoes an immediate and thorough examination by the attending provider. This inspection ensures maternal safety and involves checking the placenta’s integrity. The provider inspects both the rough maternal side (divided into segments called cotyledons) and the smooth fetal side covered by membranes. The entire organ and its surrounding membranes must be accounted for to confirm that no fragments remain inside the uterus.
Any retained placental tissue prevents the uterus from contracting fully. This inability leaves maternal blood vessels open, creating a substantial risk for postpartum hemorrhage or infection.
When Delivery Doesn’t Go as Planned
Complications in the third stage of labor primarily revolve around two issues: the placenta failing to deliver and excessive bleeding. A retained placenta is diagnosed when the organ is not expelled within a defined period, typically 30 minutes under active management or 60 minutes under expectant management.
This complication can occur if the uterus does not contract forcefully enough to detach the placenta (placenta adherens), or if the cervix closes prematurely, trapping the separated placenta inside. In some cases, the placenta may have grown too deeply into the uterine wall, known as placenta accreta spectrum, preventing natural separation entirely.
Failure of the uterus to contract forcefully after delivery, known as uterine atony, is the most common cause of postpartum hemorrhage (PPH). The relaxed uterine muscle cannot compress the blood vessels that supplied the placenta, leading to rapid blood loss.
If a retained placenta or uterine atony is identified, the provider must intervene quickly, often through manual removal of the tissue or the administration of stronger uterotonic medications to restore muscular tone.