Prenatal Ultrasound Detection of Mirror Twins With a Fused Proximal Umbilical Cord

Abstract

Placental and umbilical cord anomalies are very common developmental malformations in twin gestations, especially in the monochorionic variant. Their prenatal detection is important for planning antenatal follow-up strategies and the mode and time of delivery. In this report, we presented prenatal ultrasound (US) features, diagnostic pitfalls, the perinatal outcome, and pathologic findings of a monoamniotic twin gestation with a fused proximal umbilical cord. According to the available literature, this is the first case of a prenatally detected fused proximal umbilical cord reported to date. Written informed consent was obtained from the patient for publication of this report and accompanying images. A 30-year-old patient, gravida 4, para 3, presented to our department for routine antenatal follow-up. Ultrasound at 24 weeks revealed monochorionic monoamniotic same-sex twins with an appropriate gestational age. A fetal anatomic evaluation revealed that fetus 1 had no abnormalities, and fetus 2 had a single umbilical artery. The placenta was located anteriorly. A close evaluation of the umbilical cord with US showed 3 umbilical arteries and 2 veins enclosed by a single umbilical cord running nearly 15 cm from the placental insertion (Figure 1A). From that point onward, the cord bifurcated distally to 2 umbilical cords (Figure 1B). Antenatal follow-up was uneventful, and the neonates were delivered at 34 weeks because of monoamnionicity and recurrent cesarean deliveries. The neonates weighed 2170 and 2350 g, respectively, and were healthy with no gross anomalies. Hematocrit values of the neonates were 41.9%, and 42.5%. They had a single placenta and a single centrally inserted umbilical cord of about 15 cm that separated distally into 2 cords (Figure 2). A histopathologic examination revealed histologic characteristics of 2 umbilical veins and 3 umbilical arteries below the bifurcation (Figure 3A), a single vein and 2 arteries in fetus 1 (Figure 3B), and a single artery a single vein in fetus 2 above the bifurcation (Figure 3C). Postnatal outcomes were uneventful. Although the occipital hair whorl in infant 1 was counter clockwise, the second infant had a clockwise whorl, which is sign of mirror twinning (Figure 4). A superior number of umbilical vessels may be seen in a single proximal umbilical cord. The most common cause of this finding is the persistence of the right umbilical vein. However, 5 or more vessels in the cord, 2 of which are umbilical veins, have mostly been described as a part of conjoined twinning. Therefore, conjoined twins and umbilical cord entanglement in monoamniotic twins are the 2 most important entities in the differential diagnosis of a single proximal umbilical cord. In cord entanglement, the “Y sign,” which is created by an entangled proximal cord and separate bifurcating distal segments, is characteristic. However, in contrast to a fused cord that is only a single cord, the tail of the Y consists of 2 entangled umbilical cords