Chromosomal and Genetic Conditions

Conjoined Twins

What are conjoined twins?

When the bodies of twins connect, they are called conjoined twins. Conjoined twins begin as a single fertilized egg. Usually, a single egg develops into 1 baby. Sometimes a single egg divides in half 1 to 2 weeks after it’s fertilized. This creates a set of identical twins.

The exact cause of conjoined twinning is not known. There are 2 theories:

  • The egg divides late and does not divide completely.
  • The egg divides completely then it joins back together. The connection between the twins’ bodies may be fairly simple. They may share only a small amount of tissue, and both children may have all the organs and other structures they need. For example, the twins may be joined at the belly with a “bridge” connecting their livers.

Usually, the connection is more complex. In some cases, children may share:

  • Vital organs, like 1 heart
  • Many structures, like several parts of the digestive, genital and urinary systems
  • A large segment of the body, like all of the lower body
  • Part of the brain and skull

The twins’ symptoms may depend on which structures they share.

Types of Conjoined Twins

Doctors group conjoined twins into the following categories based on where they are joined.

  • This is the most common type of conjoined twins and is called thoracopagus (pronounced thor-uh-KOP-uh-gus). About 40% of all conjoined twins are in this group. These twins are face to face.

    In about 75% of cases, the twins share a heart. Twins joined at the chest may also share a liver, biliary tract (which carries bile from the liver to the small intestine) and upper digestive tract (esophagus, stomach and small intestine).

  • This type of conjoined twins, called omphalopagus (pronounced om-fuh-LOP-uh-gus) or xiphopagus (pronounced xi-phop-a-gus), are face to face. They may share a liver, biliary tract and upper digestive tract. About 34% of conjoined twins are in this group.

  • This type of conjoined twins, called pygopagus (pronounced pie-GOP-uh-gus), are back to back. They may share part of the lower digestive tract (large intestine, rectum and anus) and part of the skeleton, nervous system and genitals. About 18% of conjoined twins are in this group.

  • This type of conjoined twins, called ischiopagus (pronounced is-kee-OP-uh-gus), may be oriented to each other in different ways. In general, they partly face each other. They may share a liver and biliary tract, part of the upper and all of the lower digestive tract, the genital and urinary systems and part of the skeleton. About 6% of conjoined twins are in this group.

  • This type of conjoined twins, called craniopagus (pronounced kray-nee-OP-uh-gus), may share a skull, brain and other parts of the nervous system. About 2% of conjoined twins are in this group.

Outlook for Conjoined Twins

About 40% of conjoined twins are not alive when they are delivered (stillborn). About 35% die within a day after they are born. Although most sets of conjoined twins do not survive because their organs cannot support them, more conjoined twins survive now than in the past.

Advances in imaging, surgical techniques and anesthesia have helped improve chances for survival. We also have tools to detect their condition before birth so families and doctors can plan their care before they are born.

Some conjoined twins live for days, weeks, months or years while conjoined, sometimes even into adulthood. Others may need to be separated by surgery.

The success of the separation surgery depends on many factors, mainly where the twins are connected and which structures they share. In many cases, both twins survive after surgery. In some cases, only 1 survives because the other doesn’t have the organs they need or the organs are not well developed. Sometimes neither child survives.

Conjoined Twins at Seattle Children’s

Seattle Children’s provides complete care to meet all of the healthcare needs of conjoined twins from birth through childhood and into the early adult years. This may include surgery to separate the twins.

Our team has the knowledge, experience and facilities to perform separation surgeries – and to provide care for conjoined twins who cannot be separated or whose family decides not to separate them.

Separation is not the only choice for these children. Some parents may choose not to have the surgery even though their children could be separated. You will meet with a team of doctors to talk about your twins, including the benefits and risks of having surgery and of not being separated.

Our goal is to help you understand your twins’ health and all your options so you can make the choices that are best for your family.

  • Seattle Children’s is a national leader in successful surgery for conjoined twins. We base treatment plans on years of experience and the newest research on what works best – and most safely – for children and teens. This experience helps us work with you to decide on the best treatment.

    Prior to the birth of your twins, Seattle Children’s Prenatal Diagnosis and Treatment Program will help you get ready for the birth and plan the steps ahead, which may include separation surgery.

  • Many types of healthcare providers are needed to assess your twins’ condition and plan and carry out their treatment.

    Along with your children’s surgeons, you are connected with doctors trained to care for new babies with complex problems (neonatologists), nurses, dietitians, child life specialists, social workers and others. We work together to meet all of your children’s health needs and help your family through this experience.

Conjoined Twins Symptoms

Conjoined twins may be connected to each other in many different ways. Their health and any symptoms depend on how each child developed, which structures they share and how well their organs work.

Most conjoined twins are born early (premature). This means their lungs have probably not finished developing and breathing problems are common.

Conjoined Twins Diagnosis

In most cases, doctors see that twins are conjoined during a routine ultrasound late in the first trimester of pregnancy or in the second trimester. Seattle Children’s Prenatal Diagnosis and Treatment Program provides care for pregnant women and their conjoined twins.

Each set of conjoined twins is unique. Decisions about their care are complex and often hard for their families and their healthcare providers. The chance for survival is an important factor in these decisions. Another important factor is the quality of life for the twins if they stay conjoined or are separated.

  • Once your doctor can see where the twins are joined by ultrasound, the doctor will have more information on the structures the twins may share. Other imaging studies can also take pictures of the twins before birth. They include ultrasound, echocardiography and prenatal MRI (magnetic resonance imaging).

    Prior to the birth of your twins, Seattle Children’s Prenatal Diagnosis and Treatment Program will help you get ready for the birth and plan the steps ahead, which may include separation surgery. We will perform the imaging studies and explain what the images show. You can consult with Seattle Children’s doctors who care for conjoined twins about what to expect, including whether separation is possible. Some parents continue their pregnancy. Others decide to end their pregnancy.

    For parents continuing their pregnancy, doctors will suggest careful monitoring and planning. This helps the healthcare team prepare for the diagnostic tests and provide the treatments the twins may need once they are born.

    Prenatal care of conjoined twins usually includes scheduling delivery by cesarean section (C-section) a month before the twins’ due date. This is because a vaginal birth is too hard for the mother and babies.

  • After delivery by C-section, the twins will likely need many types of imaging studies and tests to learn as much as possible about how they are connected and their overall health. This information will help you and the healthcare team decide how to care for the twins.

    Studies and tests your babies need will depend on where the twins are joined and their health. A few of the common tests for conjoined twins are:

    • Heart tests, such as echocardiography and electrocardiography
    • Ultrasound
    • CT (computed tomography) scan

Conjoined Twins Treatment

The treatment that conjoined twins may need depends on the health of each twin and where and how they are joined.

  • The connection between the twins’ bodies may range from fairly simple to very complex. Both children may have all the organs and other structures they need, or they may share other structures or vital organs, like their heart. Their bodies may be able to support both their lives, or it may be hard for 1 or both to survive because of health problems. Treatment for each set of twins is unique.

    Experts from Seattle Children’s Prenatal Diagnosis and Treatment Program will work closely with each other and with you to provide the care you and your twins need before the babies are born and plan for their needs after birth.

    Before birth and in the months soon after, your twins’ healthcare team will gather as much information as they can about their anatomy and how well their bodies work. The team will use this information to create a detailed treatment plan. The main goal is to give both children the best chance for a good quality of life, whenever possible.

  • Your twins’ treatment plan may or may not include surgery to separate them.

    Some conjoined twins live for days, weeks, months or years – even into adulthood – still physically connected to each other. For conjoined twins, being connected to their sibling is “normal.” Some conjoined twins have happy, healthy, full lives by staying connected. For some twins, separation surgery is too difficult, so staying connected is the only real option.

    Some conjoined twins do have surgery to be separated, usually in the first 12 months of life. This may be the best option for the physical health of the children, while also giving them the chance to have independent bodies and lives.

    Separation surgery is sometimes the best option because the twins’ shared organs cannot support both of them. Or it may be the best option because 1 twin is unlikely to survive and separation is the only way to give the other twin a chance to live.

    Your healthcare team will speak with you about what your twins’ lives may be like whether they are joined or separated. They will help you consider which option is best for your twins.

  • Surgery to separate conjoined twins requires detailed planning whenever possible. To prepare for surgery, your twins will need providers who are experts in many different types of care. They will work together to plan the steps and timing of the surgery and the care your children will need before and after. One doctor will oversee the team and coordinate all parts of the plan.

    In most cases, doctors will do the separation surgery after your twins are at least 4 months old. This gives their bodies a chance to grow so it’s easier for doctors to do the surgery and easier for the twins to withstand the surgery. This also allows time for the many imaging studies, tests and other procedures that might be needed to learn about your twins’ bodies or prepare them for separation.

    In some cases, conjoined twins need to be separated before they are 4 months old because of a health emergency or an urgent problem that cannot wait.

    Often, 2 complete surgery teams work together very closely to separate twins. This can be important to take care of the complex needs of both twins at the same time while they are being separated and right after. Once your twins are separated, each may need additional surgeries to correct some of the anatomic (structural) problems they may have.

  • Your twins will need long-term follow-up visits throughout their childhood and into their early adult years to check their growth and development whether they stay connected or are separated. Most will need surgeries or other types of treatment for health issues that arise over time.

Contact Us

If you have questions about prenatal diagnoses or treatment options for conjoined twins, call our Prenatal Diagnosis and Treatment Program at 206-987-5629, or our General and Thoracic Surgery Department at 206-987-2794.

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