**4. Part 3: processes affecting placental perfusion**

	- i. *Subchorionic hematoma*—the partial detachment of the chorionic membranes from the endometrium due to mass effect by a hematoma. It is the most common form.
	- ii. *Subamniotic (preplacental) hematoma*—a rare form of hematoma that is contained within the amnion and chorion.
	- iii.*Retroplacental hematomas*—complete or partial detachment of the placenta from the uterine wall with a hematoma confined behind the placenta. When the Large hematomas can decrease trans-placental perfusion and lead to intrauterine growth retardation (IUGR) and oligohydramnios [118].

### *Placental Abnormalities DOI: http://dx.doi.org/10.5772/intechopen.81579*

 but before delivery of the fetus. This condition affects an estimated 1 in every 100–120 pregnancies and typically presents after 20 week of gestation; however, the gestational age-specific incidences depend on the underlying etiopathogenesis of individual cases [44, 119–121]. Placental abruption is a clinical diagnosis, and even with prompt diagnosis, the maternal and fetal morbidity and mortality can be devastating. The presentation varies from the classic scenario of postmechanical event (such as trauma) acute-onset painful life-threatening obstetrical hemorrhage with associated fetal distress noted on external fetal monitoring to incidentally identify painless concealed focal retroplacental hematomas with intraplacental anechoic areas to chronic painless vaginal bleeding [122–124]. It should be noted that ultrasound has a low sensitivity for diagnosing abruption, and therefore diagnosis should be based on clinical suspicion. Known risk factors include trauma, hypertensive disorders, preterm premature rupture of membranes (PPROM), subchorionic hematomas, and cocaine [123, 125, 126]. Management is individualized to the degree and severity of individual cases, ranging from emergent cesarean delivery for acute complete abruptions to serial surveillance and expectant management for contained retroplacental hematomas. While management of acute abruptions is part of the standard training for obstetricians, the individualized management of chronic and/or partial abruptions without evidence of fetal compromise or maternal instability is a less defined arena which must take account maternal factors (such as medical co-morbidities, hemoglobin and hematocrit level, blood type, evidence of coagulopathy, Bishop score, and patient reliability for close surveillance) as well as fetal considerations (such as gestational age, viability, fetal presentation, complications, estimated fetal weight, chorionicity, practitioners experience). It is a scenario that often leads to consultation with Maternal-Fetal Medicine specialists for assistance and guidance. The mechanical separation at the maternal-fetal interface can decrease the placental perfusion in a fashion similar to placental infarcts and acute atherosis of the spiral arteries (please see the relevant sections of this chapter) and can lead to fetal acidemia, intrauterine fetal growth restriction (IUGR), small for gestational age (SGA) neonates, chronic abruption-oligohydramnios sequence, and preeclampsia [127–129]. Abruptions with large volume hemorrhage can lead to cardiovascular compromise, disseminated intravascular coagulation (DIC), and both fetal and maternal mortality. Patients with a history of one previous placental abruption are at 3–15% risk of future abruption, and women with a history of two previous abruptions are between 20 and 25% risk of repeat abruption [44, 130–133]. Research focused on preventing placental and maternal interface infarcts is currently active with small randomized controlled trials (RCTs) demonstrating a protective effect with anticoagulants administered in a subcuticular manner [134].
