What Are Conjoined Twins?

Conjoined twins are a rare and fascinating phenomenon in the world of medicine and human development. These twins are physically attached to each other at birth, and their connection can range from a small area of skin to sharing vital internal organs. This condition presents unique challenges throughout pregnancy, delivery, and the lives of the twins after birth.

The Complexity of Separation

Some conjoined twins can be separated through complex surgical procedures. The Children’s Hospital of Philadelphia (CHOP) is a leader in this field, having successfully separated 32 pairs of conjoined twins since 1957. Dr. Holly L. Hedrick, a pediatric and fetal surgeon at CHOP, explains, “To determine if conjoined twins can be safely separated, we use detailed imaging before birth, such as fetal echocardiography, ultrasound, and MRI, to map shared organs and structures.”

The best possible outcome is a safe separation, but not all twins can be separated. The exact point of attachment and the organs involved may make separation impossible, meaning the twins remain connected for life. Regardless of whether separation is possible, conjoined twins require extensive medical care to manage their health.

After birth, further imaging—like echocardiograms and MRIs—is performed to assess the twins’ anatomy. The most common connection points are the chest and abdomen.

The Origin of “Siamese Twins”

Conjoined twins were once referred to as “Siamese twins,” a term originating from the famous pair Chang and Eng Bunker from Thailand (formerly Siam). Born in the early 1800s, they traveled the world as performers, married sisters, and fathered 22 children, living rich and full lives despite their condition.

What Causes Conjoined Twins?

Scientists are still uncertain about the exact cause of conjoined twins, but two main theories exist:

Fission: The embryo begins to split into identical twins but does not complete the process, resulting in conjoined twins.
Fusion: The embryo splits but then fuses back together at some point, leading to physical attachment.

Conjoined twins are extremely rare, occurring in about 1 in every 50,000 to 60,000 births. About 70% are female, and sadly, most are stillborn.

Conjoined twins are not linked to any particular race or maternal age. Having conjoined twins does not affect your ability to have a normal pregnancy in the future.

Conjoined Twin Pregnancy: A High-Risk Journey

Pregnancy with conjoined twins is considered high-risk and requires a multidisciplinary team for management. If the twins survive, delivery is almost always by C-section due to the risks of vaginal birth.

Diagnosing Conjoined Twins

Conjoined twins are usually detected during a routine ultrasound in the first or second trimester, sometimes as early as 7-12 weeks. If confirmed, additional tests like MRI and echocardiogram help determine where the twins are connected and which organs they share.

Symptoms and Monitoring

Pregnancy symptoms are similar to those of a typical twin pregnancy but may be more severe. Expectant mothers may experience increased tiredness, nausea, vomiting, and a rapidly growing uterus.

Once diagnosed, the pregnancy is closely monitored by a team that may include maternal-fetal specialists, pediatric surgeons, neonatologists, and others. Monthly ultrasounds, blood tests, and biophysical profiles help track the babies’ development. MRI scans in the third trimester provide detailed images for delivery planning, and sometimes life-size 3D models are created from these scans.

Unfortunately, many conjoined twin pregnancies end in miscarriage due to the high risks involved. Some parents may choose to terminate the pregnancy after weighing the survival odds and quality of life for the twins. Legal options for abortion vary widely by state, especially after the overturning of Roe v. Wade.

Birth and Immediate Care

Conjoined twins are almost always delivered by C-section to minimize risks. The delivery room is filled with specialized teams for each twin, led by neonatologists. Medical teams rehearse the procedure in advance to ensure everything goes smoothly.

After delivery, the umbilical cords are clamped quickly to prevent blood circulation issues. Doctors then examine the twins and determine the next steps, which could include emergency surgery if one twin is stillborn or critically ill.

Types of Conjoined Twins

Conjoined twins are classified by how and where they are attached:

Thoracopagus: Joined at the chest, often sharing a heart and liver.
Omphalopagus: Joined at the abdomen, sharing a liver and digestive tract.
Pyopagus: Joined at the lower back, possibly sharing genital and urinary organs.
Parapagus: Joined side-by-side at the pelvis.
Craniopagus: Joined at the head, sometimes sharing brain tissue.
Rachipagus: Joined along the spine.
Ischiopagus: Joined at the pelvis, possibly sharing lower GI tract and organs.
Cephalopagus: Joined at the head and chest, often sharing vital organs.

Can Conjoined Twins Be Separated?

Not all conjoined twins are candidates for separation. If they share vital organs such as the heart, separation is usually impossible. Doctors generally wait several months after birth to consider elective separation, allowing time for the twins to grow and for a thorough understanding of their anatomy. In emergencies, immediate separation may be necessary to save one twin’s life.

Separation surgery is highly complex and may require families to relocate for specialized care. After surgery, twins need ongoing therapy and medical support.

Some conjoined twins remain together into adulthood, needing special accommodations but often leading independent and fulfilling lives.

Survival Rates and Outlook

The prognosis for conjoined twins is challenging. Over 50% of pregnancies result in miscarriage or stillbirth, and about 35% of those delivered die within 24 hours due to organ failure. Of those who survive, only 25% are candidates for surgery, and about 60% survive the operation.

However, advances in medical imaging and surgical techniques have improved survival rates in recent years.

Key Takeaways

Conjoined twins are physically attached siblings, most commonly joined at the chest or abdomen.
Most conjoined twins do not survive birth, but those who do may be candidates for separation and can lead fulfilling lives.
Diagnosis and care require specialized medical teams and careful monitoring.
Survival rates are improving, but the condition remains rare and complex.

Conjoined Twins FAQ

What happens when one conjoined twin dies?
Usually, the surviving twin dies shortly after due to shared vital organs or blood circulation. In some cases, emergency separation may save the surviving twin.

How many conjoined twins are there in the world?
Estimates range from 1 in 50,000 to 1 in 200,000 live births.

Can conjoined twins be different genders?
Generally, no, as they originate from a single fertilized egg. Rare cases have occurred due to chromosomal changes after splitting.

Who were the oldest conjoined twins?
Lori and George Schappell, who lived to age 62. George was assigned female at birth but came out as transgender in 2007.

Conjoined twins continue to inspire awe and compassion. Their stories are a testament to human resilience, medical innovation, and the power of hope.