**2. Part 1: intrinsic placental abnormalities**

**A.** *Amniotic band syndrome (sequence)*—This congenital structural defect can lead to both minor and major malformations via entanglement of fetal structures in constricting rings. The malformations formed depend on the structure(s) entrapped in the band(s), and can range from minor constriction mediated limb abnormalities, amputation of extremities, complex body wall defects, craniofacial defects, and even gross defects non-compatible with life [1, 2]. The presumed etiopathogenesis leading to the clinical presentation of ABS is that mesodermal bands from the chorionic side of the amnion separate during early gestation and become attached to or entrap the embryo or germ disc [2–5]. Then, as the fetus grows, either via tethering bands or mechanical constriction, malformations develop. There is variance in the definition and debate regarding the associated sequences, complexes, and syndromes. When an abnormal band is noted on prenatal ultrasound, the differential diagnosis must include uterine synechiae, a residual gestational sac, and uterine septa. Once these differential diagnoses are ruled out, further investigation must be taken to identify other fetal or placental abnormalities. To date, there are no known biochemical markers or genes to definitively diagnose the syndrome, however, there is an association with chromosomal abnormalities, and therefore the work-up often includes amniocentesis for karyotype as well as single nucleotide polymorphism (SNP) microarray [6–12]. As the presentation and complications are diverse, management depends on individual cases and ranges from expectant management with intervention in the neonatal/pediatric period, to fetoscopic band transection (fetal surgery), and even termination of pregnancy. The wide range of potential malformations has led to the varied terminology frequently found in the literature, which includes but is not limited to: amniotic band syndrome, amniotic band sequence, amniotic deformity, adhesion mutilation (ADAM) sequence, amniotic band disruption complex, limb body wall complex, body wall complex with limb defects [3–5, 11, 13–18]. The confusion upon review of literature regarding the subject is immediately evident when reviewing the nomenclature. Further investigation is needed to determine if the ABS is a spectrum of one pathologic process or rather a collection of differing pathologic processes which result in similar outcomes.


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

vein atrophies and the normal human placenta develops with one large umbilical vein and two smaller umbilical arteries. Four-vessel umbilical cords are rare phenomena in which both umbilical veins and both arteries remain. This condition is associated with congenital anomalies, and when found should prompt further investigation; however, when it is an isolated finding the clinical prognosis is improved [27–29].


during membrane rupture and cervical dilation. Upon vessel avulsion, the fetus can precipitously exsanguinate, therefore, prenatal diagnosis is paramount in preventing potentially catastrophic peripartum complications [45]. The diagnostic modality of choice is transvaginal ultrasound with Doppler flow [46–48]. When diagnosed in the antepartum period, the preferred method of birth is planned cesarean delivery prior to the onset of labor or rupture of membranes.

 **L.** *Velamentous insertion of the umbilical cord*—a potentially catastrophic umbilical cord anomaly in which the umbilical vessels separate in the membranes before the cord reaches the chorionic plate. The vessels are not covered by Wharton's jelly and can therefore be easily compressed, lacerate, and rupture, leading to fetal hemorrhage [46]. The vessels are at greatest risk with rupturing of membranes as the vessels can tear. A common presenting sign is increased vaginal bleeding at the time of spontaneous rupture of membranes (SROM) or artificial rupture of membranes (AROM) [49]. Pregnancies complicated by velamentous insertion of the umbilical cord are associated with increased risk of PPROM, preterm labor, abruption, peripartum non-reassuring fetal heart tracing (NRFHT), cord avulsion requiring manual removal of the placenta, cesarean delivery, and fetal/neonatal death [31, 46, 49, 50]. When diagnosed in the antepartum period, management depends on whether or not the velamentous cord insertion is associated with vasa previa. When it is associated with vasa previa, the preferred method of birth is planned cesarean delivery prior to the onset of labor or rupture of membranes. In the absence of vasa previa, there is currently no evidence that cesarean delivery or induction of labor improve outcomes. As the vessels lack the Wharton's Jelly found in normal umbilical cords, the vessels are prone to compression and avulsion, therefore laboring patients should have continuous fetal heart rate monitoring to allow prompt diagnosis of fetal distress. Additionally, there is an increased risk of cord avulsion when traction is applied to the umbilical cord in the third stage of labor.
