**3. Placenta praevia**

embryonic and fetal development. Consequently, the placenta abnormalities can range from

Abnormal placental implantation (accreta, incretak, and percreta) is described using a general clinical term, respectively, morbidly adherent placenta (MAP) [2] or "abnormal invasive placenta" (AIP). If not diagnosed before delivery, MAP can lead to catastrophic postpartum hemorrhage, with life-threatening complications. Risk factors include increased maternal age, previous Cesarean delivery or myomectomy, multiparity, and previous intrauterine maneuvers (such as hysteroscopy and multiple dilatation and curettage [3]). The reported incidence ranges from 1:2500–1:7000 pregnancy in 2007 [4] to 1:533 deliveries in 2017 [3]. When the placental villi attach to the myometrium rather than the decidua, it is called placenta accreta; when the chorionic villi penetrate the myometrium, it is called placenta increta (e.g., **Figure 1**), whereas placenta percreta extends into the uterine serosa or adjacent organs (e.g., **Figure 2**). Placenta increta and placenta percreta are rare disorders, which represent <20% of the cases of placenta accreta [5]. These varieties can lead to more severe maternal complications (60% maternal morbidity [6], 7–10% maternal mortality [7]). The most important measure in decreasing these potentially fatal complications is the prenatal ultrasound diagnosis. In many cases, the patient's history is highly relevant. The key feature for early first-trimester diagnosis of MAP is an abnormal neovascularization in the ill-defined placental-myometrial junction detected in a color or power Doppler (2D or 3D) image [8], similar to the flow observed in an invasive mole, arteriovenous malformation, or retained products of conception. Other aspects can include focal or diffuse irregular lacunar lakes with turbulent flow typified by a high velocity (PSV, >15 cm/s) [9]. A higher number of lakes increase the risk of a presenting placenta accreta. The complete loss or disruption of the echolucent myometrial zone between the placenta and bladder is highly suggestive for MAP. When using color Doppler examination, the sensitivity and specificity of

**Figure 1.** Ultrasound color Doppler image of a case of placenta increta diagnosed in the early second trimester of pregnancy, associated with fetal demise. The surgical termination of pregnancy was performed under laparoscopic

guidance, with no complications.

structural anomalies, to function disorders, to site of implantation abnormalities [1].

**2. Placenta accreta, placenta increta, and placenta percreta**

328 Congenital Anomalies - From the Embryo to the Neonate

This type of obstetric pathology was firstly described in 1685 by Paul Portal, a French physician [17], as a major cause of hemorrhage, with a potentially life threat to the mother and the fetus. It was defined as the placenta that overlies entirely or partially the internal cervical os of the uterus. In complete praevia, the internal os is completely covered by the placenta (e.g., **Figure 3**). Placenta praevia is divided into *partial praevia* (a portion of the internal os is covered by the placenta),

**Figure 3.** Ultrasound image of complete placenta praevia percreta in a patient with a previous Cesarean section (color Doppler examination showing the penetration of the placenta into the bladder).

of 99–99.8%, if transvaginal color Doppler examination is used [20]. If unrecognized before the onset of labor, the fetal mortality rate ranges between 22.5 and 100% [22]. To improve the prenatal diagnosis, the prenatal ultrasound form should include a standard evaluation of the umbilical cord insertion site. However, some researchers demonstrated that general screening for vasa praevia is not cost-effective and is not advised [23]. There are recent reports of two main associations: velamentous insertions and vessels crossing between lobes in succenturiate or bilobate placentas [24]. Besides these strong risk factors, others include placenta praevia and conception by assisted reproductive technologies. If diagnosed with vasa praevia, elective Cesarean delivery should be proposed at 35–36 weeks [25]. Others prefer a scheduled Cesarean section at 37–38 weeks or when fetal lung maturation has been confirmed [26, 27]. The Canadian guidelines for the management of prenatally diagnosed vasa praevia include elective Cesarean section prior to the onset of labor. Also, as premature delivery is most likely, consideration should be given to administration of corticosteroids at 28–32 weeks (to promote fetal lung maturation), and hospitalization at about 30–32 weeks is advisable. Continuous electronic fetal heart rate monitoring and a rapid biochemical test for fetal hemoglobin can be considered, and if any of the above tests are abnormal, emergency Cesarean section should be performed [28]. Overall, physicians must be vigilant whenever amniotomy is performed as not all cases of vasa praevia are diagnosed antenatally. Any case of

Abnormalities of the Placenta

331

http://dx.doi.org/10.5772/intechopen.75985

**Figure 4.** Ultrasound color Doppler image showing vasa praevia.

suspicion should benefit of immediate delivery, to avoid fetal shock or demise [22].

Bilobed placenta (placenta bilobate, bipartite placenta, placenta duplex) is a placental morphological anomaly that refers to a placenta separated into two roughly equal-sized lobes, separated by membranes (e.g., **Figure 5**). If there are more than two lobes, then the placenta is called a multilobed placenta. The estimated incidence is 2–8% of placentas [29]. The pathology of this type of placenta is considered to be a result of a localized placental atrophy, as a result of poor decidualization or vascularization of a part of the uterus (dynamic placentation theory) [30]. Also, the

**5. Placenta variants**

**5.1. Bilobed placenta**

*marginal praevia* or praevia maginalis (the edge of the placenta extends to the edge of the cervical os), and *low-lying placenta* defined as within 2 cm of the cervical os, without covering it [2]. The reported incidence of the condition is 1 in 200–250 pregnancies [1]. Among the risk factors, there are prior Caesarean delivery, previous abortion, prior intrauterine surgery, smoking, multifetal gestation, increase in parity, and increased maternal age. The risk for placenta praevia is 12 times higher in women with history of placenta praevia in a previous pregnancy. Some studies demonstrated an increased rate of placental insufficiency in women with placenta praevia [18]. However, in a retrospective study of women with a complete or partial praevia, no fetal growth restriction was diagnosed [19]. The placenta location must be recorded during the ultrasound scan in the first- and early second-trimester pregnancies. If the placenta is significantly low, an additional ultrasound scan at the beginning of the third trimester allows the final diagnosis. Patients should be aware that nothing can be done to prevent placenta praevia. The appropriate delivery in placenta praevia is by Cesarean section, as dilation of the cervix causes separation of the placenta, leading to bleeding from the opened vessels. Still, in cases of a low-lying placenta, as the bleeding morbidity has proven to be limited, a vaginal delivery remains an option [1]. Every hospital must have a suitable protocol or algorithm for the management of placenta praevia, as this is a condition with high maternal and fetal morbidity and mortality [20].
