Sacrococcygeal teratomas (SCT) are the most common congenital tumors in the newborn. The prevalence rate is approximately 1 per 40,000 births, with 80% occurring in females. The majority of these tumors are external, protruding from the perineal region. Intrapelvic SCTs, by contrast, are extremely rare and difficult to diagnose in utero. Only 15% of the SCTs are entirely cystic, the majority being mixed or solid tumors. We describe a case of a fetal cystic presacral (grade IV) SCT, discovered at 22 weeks of gestation, which resulted in bilateral ureteral obstruction and hydronephrosis. This is the first known reported case of prenatally decompressing a cystic SCT via an amniotic catheter to alleviate a mass effect in the fetus.