What are the pathophysiology, diagnosis, management, and complications of monoamniotic (monochorionic diamniotic) twins with umbilical cord entanglement and conjoined twins?

From the Guidelines

Monoamniotic twins and conjoined twins are high-risk pregnancies that require intensive fetal surveillance and management to minimize complications and improve outcomes. The pathophysiology of cord entanglement in monoamniotic twins involves the cords becoming wrapped around each other as the fetuses move, potentially causing compression, reduced blood flow, and fetal demise 1. Diagnosis of monoamniotic twins is made via ultrasound showing a single placenta, no dividing membrane, and same-sex twins, with color Doppler demonstrating cord entanglement. Conjoined twins are diagnosed by ultrasound showing inseparable body parts and lack of membrane between fetuses, with MRI providing additional anatomical detail.

Pathophysiology and Diagnosis

• Monoamniotic twins develop when a single fertilized egg splits after the formation of the amniotic sac but before the formation of the chorion, resulting in twins sharing one amniotic sac 1.
• Conjoined twins result from incomplete splitting of the embryonic disc after day 13 post-fertilization, leading to twins who remain physically connected at specific anatomical sites 1.
• The risk of congenital anomalies seems to be higher for monozygotic twins that separate later, with conjoined twins representing the most extreme example 1.

Management

• Management of monoamniotic twins typically involves intensive fetal surveillance starting at 24-28 weeks with frequent ultrasounds and non-stress tests, hospitalization from 24-28 weeks until delivery, and planned cesarean delivery at 32-34 weeks after antenatal corticosteroids 1.
• For conjoined twins, management includes detailed imaging to assess shared organs, multidisciplinary team consultation, and delivery planning via cesarean section, with postnatal surgical separation if feasible based on the extent of organ sharing 1.
• Fetoscopic laser surgery is recommended as the standard treatment for stage II through stage IV twin-twin transfusion syndrome presenting between 16 and 26 weeks of gestation 1.

Complications

• Complications of monoamniotic twins include high perinatal mortality (10-20%) primarily from cord entanglement, twin-to-twin transfusion syndrome, and preterm birth 1.
• Conjoined twins face complications including surgical separation challenges, organ system dysfunction, and psychological impacts, with mortality rates varying from 10-50% depending on the extent and location of connection 1.
• The risk of adverse outcome, including small for gestational age and sIUGR, lower gestational age at birth, and IUFD, is increased in monochorionic twins with velamentous cord insertion 1.

From the Research

Pathophysiology

• Monoamniotic twins are at a high risk of perinatal mortality due to unique complications such as cord entanglement and twin-twin transfusion syndrome 2, 3, 4, 5.
• Cord entanglement is a severe complication in monoamniotic multiple pregnancies, which can lead to intrauterine death of one or both twins 6, 5.
• The presence of superficial artery-to-artery and vein-to-vein anastomoses and deep arteriovenous shunts in the placenta can also contribute to the pathophysiology of monoamniotic twin pregnancies 6.

Diagnosis

• Early diagnosis of cord entanglement in monoamniotic twin pregnancies is crucial and can be achieved through ultrasound examination, including color Doppler and pulsed Doppler velocimetry 6.
• Establishing chorionicity and amniocity in twin pregnancy is an essential part of ultrasound examination to diagnose cord entanglement and predict possible complications 5.
• Weekly follow-up with special observation of fetal behavior and use of color Doppler velocimetry can help monitor the pregnancy and detect any complications early on 6.

Management

• Management of monoamniotic twin pregnancies requires a multidisciplinary approach, including generalist obstetrician-gynecologists, maternal-fetal medicine specialists, and nursing staff 3.
• Hospital admission for fetal monitoring upon discovery of a cord entanglement at a viable gestation is recommended 4.
• Administration of corticosteroids for fetal lung maturity and timely delivery can improve neonatal outcomes 3.
• Elective Caesarean section at 32 weeks' gestation or upon reaching fetal lung maturity is often recommended 4.

Complications

• Monoamniotic twin pregnancies are associated with a high risk of perinatal death, with perinatal mortality rates ranging from 28-60% 5.
• Cord entanglement can lead to intrauterine death of one or both twins, and is a major contributor to the high perinatal mortality rates in monoamniotic twin pregnancies 6, 5.
• Twin-twin transfusion syndrome is another complication that can occur in monoamniotic twin pregnancies, which can further increase the risk of perinatal mortality 2, 3.