How Rare Are Conjoined Twins
Conjoined twins occur in about 1 in 50,000 to 1 in 100,000 births, making them a very rare condition. The rate is slightly higher in some regions and among female twins. They result from incomplete splitting of a single fertilized egg or secondary fusion of two embryos. Learn more about twinning and embryology from the NCBI.
Causes and Types of Conjunction
Most conjoined twins are identical (monozygotic) and share a single placenta. The point of connection depends on when the embryo stopped dividing, leading to types such as thoracopagus, omphalopagus, craniopagus, and pygopagus. Each type involves shared organs or structures, which affects treatment options and survival.
Survival Rates and Outcomes
Survival varies widely by anatomy and shared organs. Some pairs are not compatible with separation surgery, while others undergo complex operations with improving outcomes. Advances in imaging, anesthesia, and surgical planning have increased the number of successful separations in recent decades.
