Incidence of Craniopagus Twins
Craniopagus twins are extremely rare, occurring in approximately 1 in 2.5 million live births, representing only 2-6% of all conjoined twin cases. 1, 2, 3
Epidemiologic Context
- Conjoined twins themselves are exceedingly uncommon, with an incidence of approximately 10-20 per billion births 1
- Among conjoined twins, craniopagus (conjoined at the cranium) represents the rarest subtype, accounting for only 2-6% of cases 1, 4
- This translates to an incidence of craniopagus twins of approximately 1 in 2.5 million live births 2, 3
- A female preponderance has been documented in craniopagus cases 1
Embryologic Timing
- Craniopagus twins result from incomplete division of the embryo beyond 12-13 days after fertilization, occurring at approximately the primitive streak stage (around 13-14 days post-fertilization) 5, 6
- This late division timing results in monoamniotic monochorionic placentation 6
- For context, earlier divisions produce: dichorionic-diamniotic twins (0-3 days), monochorionic-diamniotic twins (4-8 days), and monochorionic-monoamniotic twins (8-12 days) 6
Clinical Significance
- Most craniopagus twins are either stillborn or die during the perinatal period 7
- Those who survive birth require detailed radiological evaluation and multidisciplinary surgical planning 2, 7
- To date, only 62 separation attempts in 69 well-documented cases have been reported in the literature 2
The extreme rarity of this condition means that no single hospital will encounter many cases, limiting opportunities to develop institutional expertise 4.