Spontaneous Triplet Bicorial, Triamniotic Pregnancy Complicated by A Hybrid Spectrum of Selective Fetal Growth Restriction and Twin to Twin Transfusion Syndrome

BACKGROUND: Spontaneous triplet pregnancy is a rare occurrence (1 in 8,000 pregnancies) that carries an 8.2-fold higher risk of developing monochorionic placentation compared to pregnancies resulting from assisted reproductive technologies. In this case, the coexistence of the “hybrid spectrum” (Twin-to-Twin Transfusion Syndrome [TTTS] and selective Fetal Growth Restriction [sFGR]), exacerbated by a velamentous cord insertion, influenced the diagnosis, its slow clinical progression, and the development of threatened preterm labor through various pathophysiological mechanisms, ultimately leading to the described outcome. CASE REPORT: An 18-year-old patient, Gesta 2, Para 1 (previous cesarean section), with a spontaneous dichorionic triamniotic (DCTA) triplet pregnancy. At 26.5 weeks of gestation, Stage IV TTTS (donor fetus C with hydrops: pleural effusion and ascites) and Type II sFGR were diagnosed, characterized by a 64% weight discordance and persistent absence of end-diastolic flow (AREDF) in the umbilical artery of the restricted fetus. Following the administration of corticosteroids for fetal lung maturation and neuroprotection with magnesium sulfate, the pregnancy was terminated via cesarean section due to progressive threatened preterm labor associated with progression to Stage V TTTS. Macroscopic examination of the placenta confirmed bichorionicity and a velamentous cord insertion in fetus C. Perinatal outcomes were: Newborn 1 (900 g, died at 96 h), Newborn 2 (790 g, died at 72 h), and Newborn 3 (375 g, intrauterine fetal death). CONCLUSION: Chorionicity is the primary determinant of perinatal prognosis, outweighing zygosity. Early identification of placental architecture in the first trimester and timely referral to tertiary care centers with fetal surgery capabilities are the only critical modifiable factors for improving survival in cases of the hybrid spectrum.