A 36-year-old woman, gravida 2 para 1, at 34 weeks gestation is brought to labor and delivery due to heavy vaginal bleeding. She has had no contractions, leakage of fluid, or recent trauma. The patient has received no prenatal care. Her first pregnancy ended in a full-term cesarean delivery. Temperature is 37.2 C (99 F), blood pressure is 134/86 mm Hg, and pulse is 98/min. On speculum examination, there is active heavy bleeding. An emergency cesarean delivery is performed. After delivery of the infant, the placenta cannot be removed and remains densely adherent to the uterine wall. An emergency hysterectomy is performed. Pathologic examination will most likely show which of the following?
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This patient with a placenta adherent to the uterine wall likely had placenta accreta, the abnormal attachment of placental villi directly to the uterine myometrium rather than to the endometrial decidua basalis.
The uterus normally consists of 3 distinct layers: serosa, myometrium, and endometrium. The endometrium is subdivided into the stratum functionalis and stratum basalis. In early pregnancy, progesterone stimulates decidualization of the stratum basalis, forming the endometrial decidua basalis.
Normally, fetal trophoblasts that form the placental villi attach to the endometrial decidua basalis. However, patients with prior uterine surgery (eg, cesarean delivery) can have endometrial scarring or defects that impair normal decidualization. In these patients, the absent decidua basalis results in direct placental attachment to the myometrium and a morbidly adherent placenta.
Placenta accreta is usually diagnosed on routine prenatal ultrasonography; however, in some cases (eg, no prenatal care), the diagnosis is made after fetal delivery when there is difficulty detaching the placenta. Attempts to remove the placenta typically lead to postpartum hemorrhage due to the disruption of highly vascular adhesions between the uterus and placenta.
(Choice A) Abnormal placental trophoblast proliferation is seen in gestational trophoblastic disease (eg, complete hydatidiform mole), which typically presents with vaginal bleeding and uterine enlargement. It does not cause a densely adherent placenta.
(Choice C) Wharton jelly is the gelatinous tissue surrounding the umbilical vessels that protects them from injury. Absence of Wharton jelly at the cord insertion site may be seen with vasa previa, in which the umbilical vessels become vulnerable to injury.
(Choice D) Infiltration of neutrophils into the umbilical cord may be seen with intraamniotic infection. However, additional signs of infection (eg, fever, purulent amniotic fluid) would likely be present and the placenta would not be densely adherent.
Educational objective:
Placenta accreta occurs due to abnormal attachment of the placenta directly onto the uterine myometrium. This condition most often develops because the endometrial decidua basalis is absent or defective due to previous uterine scarring (eg, prior cesarean delivery). The classic presentation is a morbidly adherent placenta that does not detach after fetal delivery.