Antenatal Diagnosis and Management of a Sacrococcygeal Teratoma in a Monochorionic Diamniotic Twin Pregnancy: A Case Report.

We present a case of a sacrococcygeal teratoma (SCT) diagnosed antenatally in one fetus of a monochorionic diamniotic twin pregnancy. A 39-year-old gravida with a history of hypothyroidism was referred at 12 weeks' gestation, when monochorionicity was confirmed. A routine second-trimester ultrasound revealed a small presacral cystic mass in Twin A, which progressively enlarged throughout pregnancy. Fetal magnetic resonance imaging at 26 weeks confirmed a well-circumscribed presacral lesion without solid components, consistent with an Altman Type I SCT. Owing to progressive growth and the associated risk of rupture, delivery was achieved by cesarean section at 36+5 weeks. Postnatal examination confirmed a large sacral mass in Twin A, with normal neonatal adaptation to extrauterine life. Surgical resection is planned within the first month of life. This case underscores the importance of prenatal imaging and multidisciplinary perinatal management in optimizing outcomes for fetuses with SCT.