[Early prenatal diagnosis of asymmetric cephalothoracopagus twins].

The authors report on one case of cephalothoracopagus Janiceps conjoined twins discovered by echography at 18 weeks' gestation. Conjoined twins have been said to occur with a frequency of 1/50,000 to 1/100,000 deliveries. The incidence of the cephalothoracopagus variety is one in three million births or one in 58 conjoined twins. Three different mechanisms that may have played a role in the abnormal development of these twins are discussed. The risk that the condition recurs in a subsequent pregnancy are to be considered negligible.