Case of the Week #591

Rohit V Sanghani (1), Javier Cortejoso (2)
(1) Ridham Hospital, Anand, Gujarat, India; (2) Centro Médico Recoletas, Valladolid, Spain

Posting Dates: Sep 30, 2023 - Oct 14, 2023

A 22-year-old G2P1 woman with no pertinent medical history came for first trimester screening with following findings:

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Answer

We present a case of first-trimester cord entanglement in monochorionic, monoamniotic twins. The patient opted to terminate the pregnancy despite being offered intensive monitoring.

Our images revealed the following findings:

Image 1, Video 1, 2 : Monochorionic monoamniotic twin showing entanglement of umbilical cords
Image 2 : 3D rendered image demonstrating monochorionic, monoamniotic twins with no intertwin membrane

**Image 1** 3D color doppler evaluation showing cord entanglement with chain-like appearance

Discussion

Monochorionic monoamniotic twin pregnancy is characterized by the presence of two fetuses sharing a single placenta and a single amniotic cavity. Its prevalence at birth is 0.8 to 1 per 10,000 pregnancies [1], approximately 1% of all twin pregnancies and 5% of all monochorionic twins [2-4]. Monoamniotic twins are the result of the late splitting of a single embryo between day 8 and day 13 after fertilization and are more common after in vitro fecundation/embryo transfer [5].

The presence of both fetuses in the same amniotic sac may predispose to cord entanglement which can result in compression of one or both cords, and fetal death. In addition, these pregnancies are subject to the risks of monochorionic twin pregnancy, which include twin-twin transfusion syndrome, twin anemiae polycythemia sequence, selective intrauterine growth restriction and twin reversed arterial perfusion sequence, as well as to the general risks of twin pregnancy such as preterm birth, increased congenital anomalies, and increased perinatal mortality [4].

Cord entanglement is pathognomonic for monoamniotic twins. It can be seen as early as 12 -13 weeks as intertwined umbilical cords showing different fetal heart rates. Cord entanglement is thought to be caused by normal fetal movement. It probably occurs early in pregnancy when the ratio of amniotic cavity to fetal size is largest, and fetal movements relative to each other are greatest. Cord entanglement is considered a key factor for increased risk of miscarriage, fetal malformations, intrauterine or neonatal death, and high perinatal mortality rates which are estimated between 15 and 30% [1, 6, 7]. Cord entanglement can appear in up to 74% of all monochorionic monoamniotic pregnancies [8]. Although cord entanglement is a specific pathology of monochorionic monoamniotic pregnancies, it can also occur in monochorionic diamniotic pregnancies after rupture of the dividing membrane [9].

Diagnostic ultrasonographic criteria currently adopted by most authors for making an accurate antenatal diagnosis of monochorionic-monoamniotic twin pregnancy include same-sex twins, a single placenta, no dividing membrane, normal amniotic fluid volume, unrestricted fetal movement, and cord entanglement [10, 11]. When the resolution of ultrasound was not as high as at present, the finding of entangled umbilical cords demonstrated the absence of a membrane separating the fetuses making it possible to diagnose a twin pregnancy as monochorionic monoamniotic [12].

On ultrasound examination two umbilical cords are seen to originate from a single placenta, occasionally at short distance from each other. Several loops of apparently intertwined umbilical cord may represent either the entangled cords of two twins, or the redundant cord of a single twin folded upon itself. It is essential to follow both cords from separate placental insertions, and from each fetal umbilicus to the entanglement [13]. Color and pulsed Doppler velocimetry play an important role in the demonstration of cord entanglement as it develops [14, 15]. The visualization of two distinct arterial waveform patterns of different heart rates within the same pulsed wave sampling gate (“galloping pattern”) is indicative of monoamnioticity and of cord entanglement in the first trimester [15]. In addition, pulsed Doppler is essential in the clinical management of this pathology. Abnormal pulsed Doppler sonographic findings range in severity from the presence of a diastolic notch, which is not indicative of an adverse perinatal outcome, to absent or reversed diastolic velocity in the umbilical artery and even pulsatile flow in the umbilical vein, possibly carrying a worse prognosis [16-19]. Prenatal mortality is also conditioned by the location of the cord entanglement, being higher in cases closer to the fetus than to the placenta [20]. Three-dimensional ultrasound (color Dopler and surface-rendered image) has been suggested as a new method for demonstrating cord entanglement [21, 22].

Perinatal outcome in monoamniotic twins has improved in recent years due to intensive fetal surveillance, which includes multiple ultrasound scans and fetal heart rate monitoring, performed either outpatient or inpatient. Balancing the risk of prematurity at various gestational ages and the risk of intrauterine death after that gestational age, most studies advocate delivery at 32 to 33 weeks with preference for caesarean section over vaginal delivery [3, 23].

References:

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