The epidemiology of conjoined twinning in Southern Africa.

Thirty-one sets of conjoined twins were born in Southern Africa during the period February 1974 to May 1982 with a striking increase in incidence in 1974 and 1975. There was no ethnic or social predilection, but clustering of cases occurred in a remote area of Zimbabwe. No aetiological agent was discovered, and there was no seasonal variation in the time of conception. Female conjoined twins accounted for 62% of cases, and twenty sets were of the thoracopagus type. Four pairs were separated, three of which were of the xiphopagus subtype and have survived.