Omphalocele-exstrophy-imperforate anus-spinal defect syndrome in a monozygotic twin pregnancy: a case report and literature review

BACKGROUND: The Omphalocele, Exstrophy, Imperforate Anus, and Spinal Defects Complex (OEIS complex) is a rare birth defect with a prevalence of 1 in 200,000-400000 pregnancies and 1 in 82,000-200000 live births. While cases in female monozygotic twins have been reported, the perinatal outcomes of the unaffected co-twin remain insufficiently addressed. CASE PRESENTATION: We report a spontaneously conceived monochorionic monoamniotic twin pregnancy where Twin B was diagnosed with OEIS. Prenatal ultrasound at 12 + 4 weeks identified an abdominal cystic mass in Twin B, which enlarged progressively until 20 + 4 weeks (7.0 × 4.7 × 6.2 cm) and then decreased (3.3 × 2.5 × 2.0 cm) at 22 weeks, suggesting cloacal membrane rupture. Further evaluations confirmed OEIS, single umbilical artery, and sacrococcygeal spinal defect in Twin B. At 33 + 6 weeks, the OEIS fetus underwent selective feticide by intrafetal laser therapy after multidisciplinary consultation, and then the caesarean section was performed. The OEIS fetus was weighed 1769 g, with no external genitalia and anus, and presented with a bulging of 3 × 4 cm at the umbilical location. The healthy co-twin (2020 g, Apgar scores 8/9 at 1/5 min) was followed up to 18 months with normal growth and development. METHODS AND RESULTS OF LITERATURE REVIEW: We conducted an extensive literature review (English and Chinese) using keywords including "OEIS syndrome/complex", "twin pregnancy", and "multiple pregnancy", analyzing 20 relevant cases of OEIS in twin pregnancies. CONCLUSIONS: Based on our case and literature review, OEIS complex is more common in monozygotic twins, with no significant gender predilection. In discordant twin pregnancies (only one fetus affected), the co-twin has a high likelihood of survival without malformations, and selective feticide should be considered. Concordant twin pregnancies (both fetuses affected) are associated with poor prognosis.