During pregnancy, the placenta provides the indispensable interface between mother and fetus (Chap. 5, p. 86). However, in part due to inaccessibility throughout gestation, the placenta’s anatomy, physiology, and molecular structure still remain some of the most understudied and intriguing topics in obstetrics. Furthermore, the parallels between placental formation and cancer afford opportunities to understand tumor biology and pathogenesis (Costanzo, 2018; Guttmacher, 2014).
Visual placental inspection by the obstetrician is recommended, but routine pathological examination is not mandatory. Indeed, specific conditions that merit submission for detailed inspection are still debated. For example, the College of American Pathologists recommends placental examination for an extensive list of indications, however many providers are not aware (Langston, 1997; Odibo, 2016). Moreover, data are insufficient to support all of these. At minimum, the placenta and cord should be inspected in the delivery room. The decision to request pathological examination should be based on clinical and placental findings (Table 6-1) (Redline, 2008; Roberts, 2008).
TABLE 6-1Some Indications for Placental Pathological Examinationa ||Download (.pdf) TABLE 6-1 Some Indications for Placental Pathological Examinationa
|Maternal Indications |
Antepartum infection with fetal risks
Oligohydramnios or hydramnios
Peripartum fever or infection
Preterm (<32 wks) delivery
Postterm (>42 wks) delivery
Suspected placental injury
Systemic disorders with known placental effects
Unexplained late pregnancy bleeding
Unexplained or recurrent pregnancy complications
|Fetal and Neonatal Indications |
|Admission to an acute care nursery |
Birth weight <10th or >95th percentile
Fetal or neonatal compromise
Infection or sepsis
Major anomalies or abnormal karyotype
Stillbirth or neonatal death
Vanishing twin beyond the first trimester
|Placental Indications |
|Gross lesions |
Markedly abnormal placental shape or size
Markedly adhered placenta
Term cord >32 cm or <100 cm
Umbilical cord lesions
Velamentous cord insertion
At term, the typical placenta weighs 470 g, is round to oval with a 22-cm diameter, and has a central thickness of 2.5 cm (Benirschke, 2012). It is composed of a placental disc, extraplacental membranes, and three-vessel umbilical cord. The disc surface that lies against the uterine wall is the basal plate, which is divided by clefts into portions—termed cotyledons. The fetal surface is the chorionic plate. Here, the umbilical cord inserts, typically in the center. Large fetal vessels that originate from the cord vessels then spread and branch across the chorionic plate before entering stem villi of the placenta parenchyma. In tracing these, fetal arteries almost invariably cross over veins. The chorionic plate and its vessels are covered by thin amnion, which can be easily peeled away from a postdelivery specimen.
During prenatal sonographic examinations, multiple societies, including the American Institute of Ultrasound in Medicine (2018), recommend identifying and ...