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Sex-discordant monochorionic dizygotic twins: a case report

Monochorionic (MC) twin pregnancy is generally associated with monozygosity (MZ) resulting from the division of a single embryo, while dizygotic (DZ) twins result from the fertilisation of two oocytes by two spermatozoa. Therefore, MZ twins are expected to be genetically and phenotypically identical (Hall 2003). Despite this belief that all MC pregnancies are MZ, in recent years several reports of sex-discordant MC twins have revealed that DZ twins can also share a chorion (Chen et al. 2013; Lee et al. 2014; Rodriguez-Buritica et al. 2015; Mayeur Le Bras et al. 2016).