Conjoined Twins

What are Conjoined Twins?

When twins are born sharing portions of internal organs and skin, they are known as conjoined twins. The babies can be joined at different areas of the body and some twins often share vital organs.

The reason why some identical twins are born conjoined is not known for certain. Identical twins are born when a fertilized egg splits in half. When conjoined twins are born, it is theorized that the egg does not split soon enough and when it does, it fails to separate entirely. The second theory is that after separation, the egg reconnects.

What are the Symptoms of Conjoined Twins?

During pregnancy, there are no indications to the mother that suggest she is carrying conjoined twins.

Symptoms include

During a standard ultrasound procedure, during the beginning of the second trimester, the doctor will be able to see that a mother is actually carrying conjoined twins.

By looking at the ultrasound, the doctor will also be able to determine the location of the body where the twins are connected. Thoracopagus twins are fused at the chest and they face each other. Omphalopagus twins are also facing each other, but they are joined along their breastbone down to their waist. Pygopagus twins are connected along their lower back. Babies who are joined in the pelvic region are classified as ischiopagus twins. Finally, Craniopagus twins are connected at their heads.

Conjoined Twins Causes

The direct causal factors of conjoined twins is still unknown. Even the process by which twins become conjoined is largely a mystery. Studies have established two main theories but little evidence in support of either hypothesis. One school of thought suggests that the egg divides too late to separate completely, while others believe the egg does divide completely, but, through some unknown reason, the two parts join back together.

In the normal development of twins, the embryo separates within eight to 12 days, forming two distinct fetuses, which continue to grow. In the case of conjoined twins, that division of the embryo takes longer to occur and research indicates that it can take up to 15 days after conception. As a result, separation stops prematurely and the two fetuses remain conjoined. The degree to which the twins remain conjoined is also a mystery. Some conjoined twins only share minimal tissue and maybe a liver, while others can be joined at the chest, breastbone, hip, or head.

How are Conjoined Twins Treated?

Many conjoined twins are separated during a surgical procedure when they reach two to four months of age. During an emergency situation, the twins may be separated soon after birth. This type of treatment is often necessary if the life of one of the twins is threatened by being joined to the other twin.

The treatment of separation surgery depends on where the twins are joined and which organs they share. The health of the babies must be analyzed to ensure they can survive the surgery. After the separation surgery, the twins may also need to have reconstructive surgical procedures.

Conjoined Twins Prevention

The direct causes of conjoined twins are unknown, so prevention is impossible at this point. Until more research uncovers the exact cause of this condition, there’s just no way to identify methods for ensuring the embryo separates fully. Additionally, how the fetuses become conjoined is just as big of a mystery as what initially causes the condition. Once studies uncover more answers, we may be able to prevent fetuses from becoming conjoined.

Future advancements may also uncover methods for separating the embryo early in development, avoiding extensive surgical procedures and reducing the number of stillborn births and infant deaths resulting from this condition. Unlike many birth defects, research hasn’t proven that genetics plays a role in developing conjoined twins. Likewise, the mother’s lifestyle habits, illnesses, trauma, or environmental issues don’t seem to play a role in causing twins to become conjoined.

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Last Reviewed:
September 19, 2016
Last Updated:
December 08, 2017