Conjoined Twins

What are conjoined twins?

Conjoined twins are twin fetuses that have connected body parts or organs. Conjoined twins are rare. Experts estimate only 1 in every 50,000 to 1 in 100,000 pregnancies involve conjoined twins.

Often, routine prenatal imaging tests show the first signs of physical connections between twin fetuses. The most common point of connection is the twins’ chests and abdomens.

Early detection gives healthcare teams, including specialists, more opportunity to plan treatment. It also gives you time to understand the issues and challenges that come with having twin babies who share physical connections.

In some cases, conjoined twins can have surgery to separate them from each other. Other times, conjoined twins remain linked to each other for a lifetime. In some circumstances, the fetuses may not be able to survive outside the mother’s body. But nearly all conjoined twins will need medical support and care throughout their lives.

What causes conjoined twins?

Experts know changes that happen during early fetal development lead to conjoined twins. The change happens when something disrupts the process that leads to identical twins. Identical twins happen when a single embryo from one egg and one sperm divide into two embryos that are close together. If an embryo division happens 12 to 14 days after fertilization, the fetal parts may remain connected or conjoined instead of forming two individual but identical twins.

How do healthcare providers diagnose conjoined twins?

Often, obstetricians detect signs of conjoined fetuses during routine prenatal ultrasounds. An ultrasound may detect conjoined twins as early as the first trimester of pregnancy.

If an ultrasound shows signs of conjoined twins, your obstetrician will refer you to a maternal fetal medicine specialist who manages complicated pregnancies, including conjoined twins.

The specialist may do an MRI to get more information about the fetuses, including the areas of the bodies that the fetuses share. Some common physical connection points are:

• Chest and abdomen (thoraco-omphalopagus): This is the most common form of connection in conjoined twins. Fetuses with this type of connection typically face each other. They may share organs, including their hearts, liver and digestive system.
• Chest only (thoracopagus): In this case, conjoined twins face each other. They may share a single heart or part of their liver.
• Abdomen only (omphalopagus): Conjoined twins that connect at the abdomen may share part of their upper digestive system, liver or biliary tract.
• Cranium (craniphagus): The fetuses connect at the cranium.
• Head to belly button (cephalogus): The conjoined twins are connected at the head, down to the belly button.

What happens after tests show conjoined fetuses?

Your maternal-fetal medicine healthcare provider will explain what you can expect during your pregnancy and birth. They work with a team that includes:

• Genetic counselors
• Pediatric surgeon specialists, like cardiothoracic, urologic or digestive surgery specialists. Your child’s care team will depend on which organs are connected.

Your care team will answer your questions and discuss potential options. They’ll also develop a plan for managing conjoined twins’ specific health issues.

What are the complications during pregnancy with conjoined twins?

The most common complications are miscarriage or stillbirth. Premature labor is very common in pregnancies involving conjoined twins. All babies born early have health risks; those health risks may further complicate care for conjoined twins.

Can conjoined twins be separated after they’re born?

In some cases, it’s possible to separate conjoined twins. Your care team will review imaging tests to identify the areas where the twins’ bodies connect so they can evaluate how separation surgery would affect the babies. In general, the options are:

• No separation: There are times when separation surgery could create life-threatening risks or cause significant medical issues. For example, surgical separation may not be an option if your babies share vital organs.
• Immediate separation: Sometimes, conjoined twins have life-threatening medical issues that affect one or both twins. In that case, their provider may do emergency surgery.
• Delayed separation: Your babies’ provider may recommend separation surgery when the babies are 9 to 12 months old. Delaying surgery gives your babies time to grow and develop.

Who decides whether conjoined twins will have separation surgery?

Your care team will make recommendations for you to consider. They’ll respect your opinions and concerns and work with you to make treatment decisions.

What’s the prognosis for conjoined twins?

Research shows that about 45% of conjoined twins are live births. But the prognosis — what you can expect — for newborn conjoined twins is poor. Often, one twin won’t live very long after they’re born because they have life-threatening medical issues. Experts estimate that about 8% of conjoined twins survive.

Conjoined twins will need medical support and other care throughout their lives. That’s the case whether they have separation surgery or remain conjoined. For example, conjoined twins may need:

• Additional surgery to manage issues like scoliosis
• Physical therapy
• Pediatric occupational therapy
• Early intervention to help with learning disabilities

What questions should I ask the healthcare team?

Conjoined twins are rare. You may not know much about the issues involved when prenatal tests show physical connections between twins. Here are some suggestions:

• Where are my twins connected, and what organs are shared?
• What specialists are available to oversee fetal development and treat my babies once they’re born?
• Can you say if separation surgery is a possibility?
• What circumstances would mean the babies need immediate separation?
• What resources are available to help me and my family manage the challenges that come with having conjoined twins?

Why do people sometimes refer to conjoined twins as Siamese twins?

That term dates to the 1800s and the lives of conjoined twins Chang and Eng, who were joined at the sternum. The twins were born in Siam (now Thailand).

Can conjoined twins be different sexes?

No, they can’t. Conjoined twins happen when a single identical twin embryo doesn’t fully divide into two. Just like identical twins, conjoined twins are always the same sex. About 70% of all conjoined twins are female.