Conjoined twins after single blastocyst transfer: a case report including detailed time-lapse recording of the earliest embryogenesis, from zygote to expanded blastocyst

Conjoined twins are estimated to occur in 1:50 000 pregnancies. Eighteen cases of pregnancies achieved by ART have been published of which three were achieved after single embryo transfer, allowing discussion of embryo characteristics. We report, to the best of our knowledge, the first case of parapagus conjoined twins after ART. Furthermore, this is the first report of conjoined twins with detailed morphokinetics of the earliest embryogenesis from zygote to expanded and hatched blastocyst stage. The case zygote had three refractile bodies, which were all allocated to one blastomere at first cleavage following an asynchronous pronuclei fading. Within 2 h, this blastomere cleaved to four and fragmented. The remaining blastomere cleaved symmetrically and regularly and a blastocyst (score: 4AB) was vitrified 120 h after IVF. Pregnancy was achieved following a frozen-thawed single blastocyst transfer. The etiopathogenetic mechanism of the origin of conjoined twins is unknown and several hypotheses exist. The morphokinetics in the present case and morphology of other reported cases will be discussed in this context.