Overview
When two babies are physically connected to each other at birth, they’re called conjoined twins. Experts don’t know exactly what causes the condition. But it likely involves splitting or fusion of very early-stage embryos soon after fertilization. All conjoined twins are identical, and about two-thirds are assigned female at birth (AFAB).
How common are conjoined twins?
Conjoined twins are rare. It’s estimated to occur only once in every 50,000 pregnancies. Because the conjoined anatomy is sometimes incompatible with life, many conjoined embryos will not survive. Up to 60% of conjoined twins are stillborn (not alive at birth) or die shortly after delivery.
Are conjoined twins always identical?
Yes. Conjoined twins are always identical. They’re also more likely to be female.
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