Trisomy 2 in an acardiac twin in a triplet in-vitro fertilization pregnancy

A case is reported of twin reversed arterial perfusion (TRAP) sequence in a triamniotic dichorionic triplet pregnancy conceived by in-vitro fertilizat ion which was diagnosed at 25 weeks of gestation by colour Doppler sonograp hy. It highlights the risk of monochorionicity-associated morbidity in mult iple pregnancies obtained by assisted conception and stresses the importanc e of chorionicity determination by early ultrasound examination. Cytogeneti c analysis of skin from the acardius showed trisomy 2 in all cells, whereas the karyotype in the monochorionic triplet was normal. This is an example of heterokaryotypic monozygotism where the chromosomal abnormality must hav e occurred during the early cleavage divisions. Aneuploidy as a possible ae tiological factor of TRAP sequence is discussed.