The placenta, as a rule, presents more or less rounded outlines, but now and again when inserted in the neighbourhood of the internal os it may take on a horseshoe-like appearance, its two branches running partialy around the oriice.
-J. Whitridge Williams (1903) he placenta is a fantastic organ in its own right. As discussed in Chapter 5 (p. 88), it provides the indispensable interface between mother and fetus. Indeed, placental anatomy, ogy, and molecular structure remain some of the most intriguing and understudied topics in obstetrics.
Although a placental examination by the obstetrician is recommended, by consensus, routine pathological examination is not mandatory. Indeed, speciic conditions that merit submission for detailed inspection are still debated. By way of example, the College of American Pathologists has recommended placental examination for an extensive list of indications (Langston, 1997). Data, however, are insuicient to support all of these.
At minimum, the placenta and cord should be inspected in the delivery room. he decision to request pathological examination should be based on clinical and placental findings (Redline, 2008; Roberts, 2008). Listed in Table 6-1 are some of the indications at Parkland Hospital for placental anatomical and histopathological examination.
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. he fetal surface is the chorionic plate, into which 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. he chorionic plate and its vessels are covered by thin amnion, which can be easily peeled away from a postdelivery specimen.
As recommended by the American Institute of Ultrasound in Medicine (2013), placental location and relationship to the internal cervical os are recorded during prenatal sonographic examinations. As visualized ultrasonically, the normal placenta is homogenous and 2 to 4 cm thick, lies against the myometrium, and indents into the amnionic sac. The retroplacental space is a hypoechoic area that separates the myometrium from the basal plate and measures less than 1 to 2 cm. The umbilical cord is also imaged, its fetal and placental insertion sites examined, and its vessels counted.
Many placental lesions can be identiied grossly or sonographically, but other abnormalities require histopathological examination for clariication. A detailed description of these
Antepartum infection with fetal risks Anti-CDE alloimmunization Cesarean hysterectomy Oligohydramnios or hydramnios Peripartum fever or infection Preterm delivery Postterm delivery
Systemic disorders with known effects Thick or viscid meconium Unexplained late pregnancy bleeding
Admission to an acute care nursery Birth weight � 10th or �95th percentile Feta! anemia
Vanishing twin beyond the first trimester alndications are organized alphabetically.
is beyond the scope of this chapter, and interested readers are referred to textbooks by Benirschke (2012), Fox (2007), and Faye-Petersen (2006) and their colleagues. Moreover, the placenta accrete syndrome and gestational trophoblastic disease are presented in detail in Chapters 20 and 41, respectively.