Monochorionic dizygotic twins with discordant genetic findings and congenital malformations

To describe prenatal evaluation and postnatal outcome of monochorionic diamniotic twins with discordant anomalies and genetic findings after intracytoplasmic sperm injection and double-embryo transfer.

A 36-year-old gravida 3 para 0 woman conceived after transfer of two blastocysts. Ultrasound identified monochorionic diamniotic twins and a liver-containing omphalocele in fetus B. Both sacs underwent separate amniocentesis. Testing included karyotyping, chromosome microarray, Beckwith-Wiedemann syndrome analysis, trio whole-exome sequencing, short tandem repeat analysis, postnatal peripheral blood fluorescence in situ hybridization, and placental histopathology.

Fetus A had mosaic 45,X[9]/46,XY[91]; fetus B had a 46,XY karyotype. Other prenatal genetic tests were unremarkable. Discordance at 11 of 21 short tandem repeat loci supported dizygosity. Following prelabor rupture of membranes at 34 + 5 weeks, two male infants were delivered by cesarean section. Twin A had hypospadias and bilateral cryptorchidism; twin B had giant omphalocele requiring surgical repair. Postnatal fluorescence in situ hybridization detected no sex-chromosome mosaicism. Placental histopathology confirmed monochorionicity.

Monochorionicity does not exclude dizygosity after assisted reproduction. Separate sampling of both sacs may inform discordant cases, and prenatal-postnatal discrepancies in 45,X/46,XY mosaicism warrant cautious longitudinal interpretation.