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Twin Pregnancy Complications

Our long experience with prenatal diagnosis and planning for optimum care allows us to offer the highest quality treatment whether intervention is indicated before or after birth.

Under the direction of Dr. Michael Harrison, the Fetal Treatment Center was the first institution to develop fetal surgery techniques. The first open fetal surgery in the world was performed at UCSF over 2 decades ago. We presently have more experience with fetal surgery and endoscopic fetal intervention (FETENDO fetal surgery) than any other institution in the world. We are dedicated to twin complication research and treatment innovation.

What are twin pregnancy complications?

There are several serious problems that can occur in twin pregnancies. At particular risk are pregnancies in which the twins share a placenta. These are called monochorionic (MC) twin pregnancies and they are by definition identical twins. There are essentially always vascular connections in the placenta shared by the two fetuses in this situation. As a result of these connections, in about 15% of cases an imbalance in the circulations of the fetuses can develop. In these instances, there may be significant, transfer of blood from the so-called “donor” twin to the volume-overloaded recipient twin, resulting in twin-twin transfusion syndrome (TTTS). There are other serious problems limited to MC twin pregnancies, but TTTS is the most common.

What is Twin to Twin Transfusion Syndrome (TTTS)?

Twin to Twin Transfusion Syndrome (TTTS) is a serious, progressive disorder that affects up to 15% of MC twins. The twins do not have malformations, but one transfuses the other through a particular blood vessel connection. In this situation, an artery from the donor twin enters the placental substance to exchange oxygen and nutrients. Unfortunately, the corresponding vein returns "by mistake" to the other twin (the recipient) via this arterio-venous connection.

Learn more about Twin to Twin Transfusion Syndrome (TTTS)

What is unequal placental sharing?

Not all MC twin pregnancies in which there is a difference in size of the twins and different levels of amniotic fluid, is TTTS the cause. These findings are also seen in unequal placental sharing. In this case the twins do not have an equal access to the placenta.

Learn more about unequal placental sharing

What is an acardiac twin or the TRAP sequence?

This is a very rare problem, happening on average once in every 35,000 pregnancies. One twin is usually completely normal. The other is body-like tissue, often with legs and a lower body, but no upper body or heart.

Learn more about acardiac twin or TRAP sequence