**5.2. Circumvallate placenta**

Circumvallate placenta represents one type of an extrachorial placenta, defined as an annularly shaped placenta with raised edges composed of a double fold of chorion, amnion, degenerated decidua, and fibrin deposits [1]. Pathologically, the basal plate is larger than the chorion frondosum [31]. The incidence of circumvallate placenta has been reported in 0.5–18% of placentae examined after delivery [32, 33]. There is an increased risk of vaginal bleeding at the beginning of the first trimester and also a risk of premature rupture of the membranes, preterm delivery, placental insufficiency, and placental abruption [34, 35]. The pregnancy outcome can be very poor. Prenatally, during the ultrasound scan, circumvallate placenta can be suspected as a peripheral rim of chorionic tissue appearing as an echodense ridge (placental shelf), with a "tire sign" appearance on the 3D exam [36]. However, the diagnosis is made most often after delivery, by inspection of the placenta. If circumvallate placenta is suspected antenatally, the pregnancy should be classified as a high-risk pregnancy, and special precautions should be considered, to prevent preterm labor. A high association between circumvallate placenta and a single umbilical artery [37] and no relationship between the amniotic band syndrome or limb body wall complex and circumvallate placenta have been reported [31]. Thus, the condition carries no risk of fetal deformity. Circummarginate placenta is another type of extrachorial placenta, with no clinical significance, where the transition from membranous to villous chorion is flat [1].

**Figure 5.** Ultrasound image (gray scale and color Doppler) of a bilobed placenta, showing the two lobes of the placenta and the umbilical cord insertion in one of the lobes.

#### **5.3. Placenta membranacea**

genetic origin has been considered, as the risk of a bipartite placenta is greater in a woman with already a history of bipartite placenta. Frequent association with a velamentous insertion of the cord is reported, as the umbilical cord may insert in either lobe or in between the lobes. The diagnosis of bilobed placenta is made by ultrasound assessment when two separate placental discs of nearly equal size are noted. In cases of bilobed placenta, there is no increased risk of fetal anomalies. However, this type of placental abnormality can be associated with first-trimester bleeding, polyhydramnios, abruption, and retained placenta. Also, it can increase the incidence of vasa praevia with a high incidence of hemorrhage. Taking all these risk factors into consideration, a bilobed placenta does not have any unfavorable short-term or long-term pregnancy outcomes.

Circumvallate placenta represents one type of an extrachorial placenta, defined as an annularly shaped placenta with raised edges composed of a double fold of chorion, amnion, degenerated decidua, and fibrin deposits [1]. Pathologically, the basal plate is larger than the chorion frondosum [31]. The incidence of circumvallate placenta has been reported in 0.5–18% of placentae examined after delivery [32, 33]. There is an increased risk of vaginal bleeding at the beginning of the first trimester and also a risk of premature rupture of the membranes, preterm delivery, placental insufficiency, and placental abruption [34, 35]. The pregnancy outcome can be very poor. Prenatally, during the ultrasound scan, circumvallate placenta can be suspected as a peripheral rim of chorionic tissue appearing as an echodense ridge (placental shelf), with a "tire sign" appearance on the 3D exam [36]. However, the diagnosis is made most often after delivery, by inspection of the placenta. If circumvallate placenta is suspected antenatally, the pregnancy should be classified as a high-risk pregnancy, and special precautions should be considered, to prevent preterm labor. A high association between circumvallate placenta and a single umbilical artery [37] and no relationship between the amniotic band syndrome or limb body wall complex and circumvallate placenta have been reported [31]. Thus, the condition carries no risk of fetal deformity. Circummarginate placenta is another type of extrachorial placenta, with no clinical

significance, where the transition from membranous to villous chorion is flat [1].

**Figure 5.** Ultrasound image (gray scale and color Doppler) of a bilobed placenta, showing the two lobes of the placenta

**5.2. Circumvallate placenta**

332 Congenital Anomalies - From the Embryo to the Neonate

and the umbilical cord insertion in one of the lobes.

Placenta membranacea is an extremely uncommon variation in placental morphology, in which the placenta develops as a thin structure, occupying the entire periphery of the chorion. This type of placental abnormality is classified as *diffuse placenta membranacea* (with chorionic villi covering the fetal membranes completely) and *partial placenta membranacea* [1]. The estimated incidence is 1:20,000–1:40,000 pregnancies [38], with an association of abnormal placental adherence in up to 30% of cases [38]. The ultrasound assessment is useful, but being an extremely rare variant, there are no reports of its sensibility and specificity. The common symptom of this type of placental pathology is vaginal bleeding in the second or third trimester (often painless) or during labor. Complications such as antepartum hemorrhage, second-trimester miscarriages, fetal demise, and postpartum hemorrhage have been reported in pregnancy with placenta membranacea [39]. Placenta praevia and placenta accrete or intrauterine growth restriction can also be associated with this condition, worsening the maternal and fetal prognosis [30, 40].
