OEIS complex (omphalocele-exstrophy-imperforate anus-spinal defects) in monozygotic twins: a case report and literature review

The omphalocele-exstrophy-imperforate anus-spinal defects (OEIS) complex represents severe midline abdominal and pelvic defects of unknown etiology. This complex is rare, affecting 1 in 200,000 to 400,000 pregnancies and is extremely rare in twin or triplet gestations. Here, we report the OEIS complex in a spontaneous monozygotic twin pregnancy and previously reported OEIS complex in twin or triplet pregnancy are reviewed. Spontaneous pregnancy and unremarkable family history, but concordance of monozygotic twins for the defect may support the theory that early malformation complexes, e.g., OEIS, may be related to errors in monozygotic splitting in early blastogenesis.