Table of ContentsView AllTable of ContentsCausesTypesDiagnosisSeparation SurgeryFrequently Asked Questions
Table of ContentsView All
View All
Table of Contents
Causes
Types
Diagnosis
Separation Surgery
Frequently Asked Questions
Conjoined twins occur when identical twins have fused bodies before they are born. This condition has also been known as “Siamese twins,” named after the first world-recognized set of conjoined twins born in 1811 in Siam, present-day Thailand.“Siamese twins” is now an inappropriate, outdated term.
Unfortunately, the majority of conjoined twins die before birth or shortly thereafter. The prognosis for separating conjoined twins depends on where their bodies are connected.
This article discusses the causes, types, and diagnosis of conjoined twins, as well as separation surgery.
How Many Twins Are Born Conjoined?The exact occurrence of conjoined twins is not known, but it’s estimated to be between 1 in 30,000 to 1 in 200,000.
How Many Twins Are Born Conjoined?
The exact occurrence of conjoined twins is not known, but it’s estimated to be between 1 in 30,000 to 1 in 200,000.
Edwin Tan / Getty Images
Conjoined twins are a rare occurrence, which makes it more difficult to determine the exact cause. However, there are two theories about the possible causes of conjoined twins.
Conjoined twins are alwaysidentical twins. When identical twins form in utero, one fertilized egg, called an embryo, splits into two separate individuals. The main theory for conjoined twins is that this splitting process isn’t complete.
The second theory for conjoined twins suggests that two separate embryos fuse together while they are developing.
Types of Conjoined Twins
Most common types are:
Least common types are:
What Are Mono Mono Twins?
Conjoined twins are typically diagnosed early on in pregnancy, with the earliest reported diagnosis at eight weeks of gestation.Conjoined twins are diagnosed with various types of imaging, including:
Pregnancy Risks
Conjoined Twin Separation Surgery
There are many factors that go into a decision to perform separation surgery, including the extent of shared organs and the surgeries that will be required to reconstruct body parts after separation surgery. In addition, there are ethical considerations, as surgery can result in the death of one or both of the babies.
Not all conjoined twins are candidates for surgery, such as when the babies share a heart. Separation surgery is a very complex procedure that requires multiple health care professionals with varying areas of expertise, including:
Preparation for separation surgery often includes putting tissue expanders under the skin to stretch it out to provide skin for covering the area that is separated during surgery.
About 60% of separation surgeries are successful.
Conjoined Twins Successfully SeparatedTwins who are joined at the head typically have a poor prognosis. However, in October 2020, a pair of 9-month-old craniopagus twins were successfully separated at the University of California, Davis, Children’s Hospital. The procedure lasted 24 hours.
Conjoined Twins Successfully Separated
Twins who are joined at the head typically have a poor prognosis. However, in October 2020, a pair of 9-month-old craniopagus twins were successfully separated at the University of California, Davis, Children’s Hospital. The procedure lasted 24 hours.
Summary
A Word From Verywell
Receiving the news that you’re carrying conjoined twins can be overwhelming. Working closely with your care team and learning about your condition can help you know what to expect during your pregnancy.
Frequently Asked QuestionsConjoined twins are always delivered via C-section and are often born early.Because conjoined twins develop from one fertilized egg, they are always identical.The majority of conjoined twins die in utero or shortly after birth. However, some conjoined twins live into adulthood. The oldest conjoined twins on record lived to be 68 years old.
Conjoined twins are always delivered via C-section and are often born early.
Because conjoined twins develop from one fertilized egg, they are always identical.
The majority of conjoined twins die in utero or shortly after birth. However, some conjoined twins live into adulthood. The oldest conjoined twins on record lived to be 68 years old.
10 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Mathew RP, Francis S, Basti RS, et al.Conjoined twins – role of imaging and recent advances. J Ultrason. 2017;17(71):259-266. Doi:10.15557%2FJoU.2017.0038Standford Children’s Health.Conjoined twins.Children’s Hospital Colorado.Conjoined twins.Children’s Hospital of Philadelphia.Conjoined twins.Liang XW, Cai YY, Yang YZ, Chen ZY.Early ultrasound diagnosis of conjoined twins at eight weeks of pregnancy: A case report. World J Clin Cases. 2020;8(21):5389-5393. Doi:10.12998%2Fwjcc.v8.i21.5389Sparrow Health Systems.Conjoined twins.Savulescu J, Persson I.Conjoined twins: philosophical problems and ethical challenges. J Med Philos. 2016;41(1):41-55. doi:10.1093%2Fjmp%2Fjhv037Afzal AR, Montero FJ.Conjoined twins. In:StatPearls. StatPearls Publishing; 2021.UC Davis Children’s Hospital.Rare set of conjoined twins successfully separated in 24-hour surgery at UC Davis Children’s Hospital.ABC News.World’s longest-surviving conjoined twin brothers die at 68.
10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Mathew RP, Francis S, Basti RS, et al.Conjoined twins – role of imaging and recent advances. J Ultrason. 2017;17(71):259-266. Doi:10.15557%2FJoU.2017.0038Standford Children’s Health.Conjoined twins.Children’s Hospital Colorado.Conjoined twins.Children’s Hospital of Philadelphia.Conjoined twins.Liang XW, Cai YY, Yang YZ, Chen ZY.Early ultrasound diagnosis of conjoined twins at eight weeks of pregnancy: A case report. World J Clin Cases. 2020;8(21):5389-5393. Doi:10.12998%2Fwjcc.v8.i21.5389Sparrow Health Systems.Conjoined twins.Savulescu J, Persson I.Conjoined twins: philosophical problems and ethical challenges. J Med Philos. 2016;41(1):41-55. doi:10.1093%2Fjmp%2Fjhv037Afzal AR, Montero FJ.Conjoined twins. In:StatPearls. StatPearls Publishing; 2021.UC Davis Children’s Hospital.Rare set of conjoined twins successfully separated in 24-hour surgery at UC Davis Children’s Hospital.ABC News.World’s longest-surviving conjoined twin brothers die at 68.
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Mathew RP, Francis S, Basti RS, et al.Conjoined twins – role of imaging and recent advances. J Ultrason. 2017;17(71):259-266. Doi:10.15557%2FJoU.2017.0038Standford Children’s Health.Conjoined twins.Children’s Hospital Colorado.Conjoined twins.Children’s Hospital of Philadelphia.Conjoined twins.Liang XW, Cai YY, Yang YZ, Chen ZY.Early ultrasound diagnosis of conjoined twins at eight weeks of pregnancy: A case report. World J Clin Cases. 2020;8(21):5389-5393. Doi:10.12998%2Fwjcc.v8.i21.5389Sparrow Health Systems.Conjoined twins.Savulescu J, Persson I.Conjoined twins: philosophical problems and ethical challenges. J Med Philos. 2016;41(1):41-55. doi:10.1093%2Fjmp%2Fjhv037Afzal AR, Montero FJ.Conjoined twins. In:StatPearls. StatPearls Publishing; 2021.UC Davis Children’s Hospital.Rare set of conjoined twins successfully separated in 24-hour surgery at UC Davis Children’s Hospital.ABC News.World’s longest-surviving conjoined twin brothers die at 68.
Mathew RP, Francis S, Basti RS, et al.Conjoined twins – role of imaging and recent advances. J Ultrason. 2017;17(71):259-266. Doi:10.15557%2FJoU.2017.0038
Standford Children’s Health.Conjoined twins.
Children’s Hospital Colorado.Conjoined twins.
Children’s Hospital of Philadelphia.Conjoined twins.
Liang XW, Cai YY, Yang YZ, Chen ZY.Early ultrasound diagnosis of conjoined twins at eight weeks of pregnancy: A case report. World J Clin Cases. 2020;8(21):5389-5393. Doi:10.12998%2Fwjcc.v8.i21.5389
Sparrow Health Systems.Conjoined twins.
Savulescu J, Persson I.Conjoined twins: philosophical problems and ethical challenges. J Med Philos. 2016;41(1):41-55. doi:10.1093%2Fjmp%2Fjhv037
Afzal AR, Montero FJ.Conjoined twins. In:StatPearls. StatPearls Publishing; 2021.
UC Davis Children’s Hospital.Rare set of conjoined twins successfully separated in 24-hour surgery at UC Davis Children’s Hospital.
ABC News.World’s longest-surviving conjoined twin brothers die at 68.
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