Why Does Placental Retention Commonly Occur?
Placental retention refers to the condition where, during the third stage of labor, 30 minutes after the birth of the fetus, part or all of the placenta remains within the uterus, leading to a high risk of postpartum hemorrhage. Common causes of placental retention include uterine inertia, uncoordinated uterine contractions, placental adhesion or implantation, obstructed placental expulsion, and human factors. Prompt placental separation is essential in such cases.
1. Uterine Inertia
After the delivery of the fetus, if the mother's uterine contractility is very weak and insufficient to cause complete separation of the placenta, placental retention can occur. In this situation, postpartum hemorrhage is generally not caused. However, if the uterine contractions are relatively weak and partial placental separation occurs, it can also lead to placental retention and significant postpartum bleeding. Uterine inertia is the most common cause of placental retention.
2. Uncoordinated Uterine Contractions
Normal uterine contractions begin at the two uterine corners, with the contractile force concentrating first in the middle of the uterine fundus and then spreading to the lower uterine segment. The contractile force is strongest at the fundus. If the contractions are uncoordinated, resulting in uterine inlet spasms or narrowing, it can cause placental retention within the uterine cavity.
3. Placental Adhesion or Implantation
Partial adhesion between the placenta and the uterine wall, or the growth of placental villi into the uterine muscle, resulting in implanted placenta, can prevent complete placental separation from the uterus, leading to placental retention and excessive bleeding. This condition is relatively rare and typically occurs in mothers who have undergone multiple deliveries, abortions, or intrauterine infections.
4. Obstructed Placental Expulsion
Even when the placenta has completely separated from the uterus, factors such as weak abdominal or uterine muscle contractions or a full bladder can obstruct its expulsion, leading to placental retention.
5. Human Factors
These are primarily due to improper management during the third stage of labor. A common scenario involves the rupture of the umbilical cord during traction. In the third stage, some mothers may require oxytocin injection to enhance uterine contractions, facilitating placental separation from the uterine wall. During this process, a midwife may place one hand on the mother's abdomen to stabilize the uterus while gently pulling on the umbilical cord with the other hand. If the placenta has already separated, it can be easily expelled through the vagina. However, if the placenta is not fully separated and the umbilical cord is thin, it can easily rupture, leading to a narrowing of the cervical os and placental retention.
