Delivery of the placenta occurs in two stages: (1) separation of the placenta from the wall of the uterus and into the lower uterine segment and/or the vagina, and (2) actual expulsion of the placenta out of the birth canal. There are two approaches to delivery of the placenta: active management and physiological management. These have been compared in a number of trials, and active management is recommended because it reduces the incidence of PPH (blood loss >1000 mL) and shortens the third stage.
Active management consists of:
Oxytocin (10 international units [IU]) should be given by intramuscular injection, preferably after delivery of the fetal head or after delivery of the body. An equally effective alternative is oxytocin 5 IU plus ergot alkaloid (called Syntometrine as used commonly in the United Kingdom), although there is a higher incidence of nausea with this combination.
Separation of the Placenta
Placental separation takes place, as a rule, within 5 minutes of the end of the second stage. Signs suggesting that detachment has taken place include:
Gush of blood from the vagina
Lengthening of the umbilical cord outside the vulva
Rising of the uterine fundus in the abdomen as the placenta passes from the uterus into the vagina
Uterus becoming firm and globular
Expulsion of the Placenta
When these signs have appeared, the placenta is ready for expression. This is achieved by the Brandt-Andrews maneuver. This procedure involves exerting gentle traction on the cord by one hand while the other hand applies upward counterpressure on the uterus above the symphysis pubis. It is wise to avoid rough manipulations of the uterus before placental separation has taken place. Such actions do not hasten delivery of the placenta and may lead to excessive bleeding (Fig. 19-1). The average blood loss during the third stage is 250 to 500 mL.
Expulsion of the placenta.
Women at low risk of PPH who request physiological management of the third stage should be supported in their choice. Physiological management consists of:
No routine use of uterotonic drugs
No clamping of the cord until pulsation has ceased
Delivery of the placenta by maternal effort
If there is hemorrhage, failure to deliver within 1 hour of physiological management, or increased risk of PPH, then active management should be implemented. Women at higher risk of PPH include those with: (1) an overdistended uterus (multiple pregnancy, polyhydramnios); (2) high parity; (3) history of previous PPH; (4) prolonged labor, especially when associated with ineffective uterine contractions; (5) deep general anesthesia; (6) difficult operative delivery; and (7) induction or augmentation of labor by oxytocin. They should be managed actively.
Early cord clamping as part of active management is associated with a reduction in PPH. Delaying clamping of the cord by at least 3 minutes or until it has stopped pulsating has been shown to reduce the incidence of anemia in the baby by giving an infusion of blood from the placenta. This benefit is particularly seen in lower-income countries.
There is limited medium-level evidence from trials in high-income countries showing that delayed cord clamping reduced the incidence of anemia and increases in hyperbilirubinemia in the baby. Other longer-term outcomes are reported variably. There is high-level evidence from low- to middle-income countries that delayed cord clamping reduces the incidence of anemia in the baby.
Delivery of the Membranes
In most cases, as the placenta is born, the membranes peel off from the endometrium and are delivered spontaneously. Occasionally, this does not take place, and the membranes are removed by gentle traction with forceps (Fig. 19-2). Retention of small bits of membrane does not usually seem to lead to any untoward effects.
Delivery of the membranes.
Examination of the Delivered Placenta
Examination of the delivered placenta is performed to see that no parts are missing (i.e., left in the uterus). Torn blood vessels along the edge suggest that an accessory lobe may have remained in the uterus. Some obstetricians believe that examination of the placenta does not ensure that fragments have not been left behind, and they explore the uterine cavity manually after each delivery. Even with the best efforts, retained products, usually manifested by delayed PPH, will occur in about 1 percent.
Delayed Separation and Delivery of the Placenta
The third stage of labor is diagnosed as prolonged if not completed within 30 minutes of the birth of the baby with active management and 60 minutes with physiological management.
Retention of the placenta in utero falls into four groups:
Separated but retained: There is failure of the forces that normally expel the placenta
Separated but incarcerated: An hourglass constriction of the uterus, or cervical spasm, traps the placenta in the uterus
Adherent but separable: In this situation, the placenta fails to separate from the uterine wall. The causes include failure of the normal contraction and retraction of the third stage, an anatomic defect in the uterus, and an abnormality of the decidua, which prevents formation of the normal decidual plane of cleavage
Adherent and inseparable: Here are the varying degrees of placenta accreta spectrum disorders. The normal decidua is absent, and the chorionic villi are attached directly to and through the myometrium (see later in this chapter)
Manual Removal of the Placenta
Current practice is to remove the placenta manually if it does not deliver within 30 to 60 minutes after the birth of the baby, provided bleeding is not excessive. If hemorrhage is profuse, the placenta must be removed immediately. An intravenous infusion is set up and blood is made available; anesthesia may be necessary. The procedure is carried out under aseptic conditions.
The uterus is steadied by one hand holding the fundus through the maternal abdomen and applying downward counterpressure (Fig. 19-3). The other hand is inserted into the vagina and through the cervix into the uterine cavity. The placenta is reached by following the umbilical cord. If the placenta has separated, it is grasped and removed. The uterus is then explored to be sure that nothing has been left.
Manual removal of the placenta.
If the placenta is still adherent to the uterine wall, it must be separated. First some part of the margin of attachment is identified and the fingers inserted between the placenta and the wall of the uterus. The back of the hand is kept in contact with the uterine wall. The fingers are forced gently between the placenta and uterus, and as progress is made, they are spread apart. In this way, the line of cleavage is extended, the placenta is separated from the uterine wall, and it is then extracted. Oxytocics are given to ensure good uterine contraction and retraction.
Manual Exploration of the Uterus
Manual exploration of the uterus for tears or retained products is required if there is PPH not responsive to therapy. Lacerations of the uterus and cervix should also be excluded by careful inspection.
Placenta previa should be suspected antenatally in women with a history of vaginal and/or an unstable lie. Ultrasound should preferably be performed in late pregnancy to confirm location. Where available, transvaginal sonography is the preferred modality and the distance from the placental edge to the internal os should be measured. In women where the placental edge overlaps the internal os after 36 weeks’ gestation [placenta previa], cesarean section is indicated. Where the placenta is low-lying but does not overlap the internal os, patients can be divided into 2 groups: those with the placental edge ≤10 mm from the cervical os versus 11 to 20 mm from the cervical os. The risk of antepartum hemorrhage is 29 versus 3 percent, respectively, and the likelihood of a vaginal delivery is 9 to 38 percent versus 57 to 93 percent, respectively, with 75 to 80 percent of deliveries occurring at term. A trial of labor is recommended in women with the placental edge 11 to 20 mm from the cervical os; a trial of labor can also be considered in carefully selected women with the placental edge ≤10 mm from the cervical os and without risk factors for significant hemorrhage. These include recurrent antepartum hemorrhage, thick placental edge greater than 1 cm, short cervical length less than 2 cm with low-lying placenta, previous cesarean delivery, and evidence of invasive placentation.