Monochorionic

Monochorionic

Monochorionic refers to a type of twin pregnancy where the twins share a single chorion, the outer membrane that surrounds the fetus in the womb. This condition is specific to identical twins, also known as monozygotic twins, which result from the splitting of a single fertilized egg. Monochorionic pregnancies are associated with unique medical considerations and potential complications that require careful monitoring and management.

Overview

Monochorionic twins develop when a single zygote splits into two embryos after fertilization. This splitting occurs at a stage when the chorion has already formed, resulting in both embryos sharing the same chorionic sac. However, they typically have separate amniotic sacs, a condition known as monochorionic-diamniotic (MCDA) twins. In rarer cases, the twins may also share the same amniotic sac, known as monochorionic-monoamniotic (MCMA) twins.

Complications

Monochorionic pregnancies are at higher risk for certain complications compared to dichorionic pregnancies, where each twin has its own chorion. Some of the key complications include:

• Twin-to-Twin Transfusion Syndrome (TTTS): This occurs when there is an imbalance in the blood flow between the twins through shared placental vessels, leading to one twin receiving more blood than the other.
• Selective Intrauterine Growth Restriction (sIUGR): One twin may receive less blood and nutrients, resulting in restricted growth compared to the other twin.
• Twin Anemia-Polycythemia Sequence (TAPS): A less common condition where one twin becomes anemic while the other becomes polycythemic due to small blood vessel connections.
• Cord Entanglement: In MCMA twins, the absence of a separating membrane increases the risk of umbilical cord entanglement, which can be life-threatening.

Diagnosis

Monochorionic pregnancies are typically diagnosed through ultrasound imaging. Key ultrasound findings include:

• A single placenta with no dividing membrane between the twins.
• The presence of a "T-sign" at the junction of the amniotic sacs, indicating a shared chorion.

Early and accurate diagnosis is crucial for the management and monitoring of potential complications.

Management

Management of monochorionic pregnancies involves regular monitoring through ultrasound to assess fetal growth, amniotic fluid levels, and signs of TTTS or other complications. Interventions may include:

• Laser Photocoagulation: A procedure used to treat TTTS by sealing off abnormal blood vessel connections in the placenta.
• Amnioreduction: Removal of excess amniotic fluid in cases of polyhydramnios associated with TTTS.
• Close Monitoring: Frequent ultrasounds and non-stress tests to monitor fetal well-being.

Prognosis

The prognosis for monochorionic twins varies depending on the presence and severity of complications. With early detection and appropriate management, many monochorionic twins can be delivered safely. However, the risk of preterm birth and other complications remains higher than in dichorionic pregnancies.

Also see

• Twin-to-Twin Transfusion Syndrome
• Monozygotic Twins
• Dichorionic Twins
• Intrauterine Growth Restriction