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Introduction: Fetal sacrococcygeal teratomas (SCGT), the most common fetal neoplasm diagnosed in fetuses, are a rare condition with an estimated incidence of 1 in 40,0000 live births. Fetal SCGT is usually suspected when characteristic findings are seen on ultrasound such as a mass that is cystic and/or solid and is located in the sacral region. MRI may also be used to more accurately characterize the tumor and to help distinguish between SCGTs and distal neural tube defects like sacral meningomyelocele. Despite advances in ultrasound and MRI, only approximately 50% are diagnosed prenatally. The detection of fetal SCGT is important because it changes pregnancy monitoring and management as it is associated with fetal hydrops, intrauterine death, polyhydramnios, mirror syndrome, and mortality rates as high as 43%. Once an SCGT has been identified, serial ultrasound evaluation of the fetus, placenta, and SCGT is important to identify early signs of fetal hydrops, fetal anemia, or cardiac failure and to intervene as appropriate. Case Report: A 40-year-old G5P4004 was referred to Maternal Fetal Medicine (MFM) due to findings of a 1 cm mass near the fetal bladder on first trimester ultrasound. She had a level II ultrasound performed by MFM at 16.2 weeks where a 3.6 x 2.3 x 2.6 cm mass was identified. This mass was adjacent to the sacrococcygeal region. Due to its location and characteristic appearance, with both cystic and solid components with high vascularity, a fetal sacrococcygeal teratoma was suspected. There were no signs of hydrops or fetal anemia. At this time, the recommendation for management was: ultrasounds every 2 weeks to assess for hydrops and fetal anemia, growth ultrasound every 4 weeks, an echocardiogram by pediatric cardiology at 22-24 weeks, a fetal MRI at 28 weeks, and delivery between 37-39 weeks or earlier pending clinical course. At 24.2 weeks, she developed polyhydramnios with a maximum vertical pocket (MVP) of 10.5 cm. She had also failed her 1-hour glucose tolerance test with a value of 287 mg/dL. Due to the new finding of polyhydramnios and diagnosis of gestational diabetes, her monitoring was increased to weekly, with biophysical profile (BPP) starting at 28 weeks and weekly nonstress tests (NST) at 32 weeks. A fetal MRI was performed at 26.4 weeks and showed a large lesion extending off the sacrococcygeal region measuring 9.6 x 6.3 x 7.7 cm that was composed of both solid and cystic components. By 32.2 weeks, she developed severe polyhydramnios with an AFI of 36.0 cm and accelerated fetal growth due to an AC > 99th percentile. The last ultrasound she had at 34.2 weeks the SCGT measured 17.7 x 13.3 x 13.6 cm and severe polyhydramnios persisted. The patient went into preterm labor at 35.2 weeks and had a cesarean section due to known SCGT measuring greater than 5 cm. Immediately after delivery, the neonate was evaluated by the neonatal team and transferred to the Neonatal Intensive Care Unit. The infant had surgical resection of the mass and will have tumor markers, AFP and LDH, monitored for development of recurrent immature or mature teratoma. The pathology report confirmed the diagnosis for benign sacrococcygeal teratoma. Discussion: Failure to diagnose a fetal sacrococcygeal teratoma has potentially catastrophic consequences for the fetus and mother. Maternal complications include hyperemesis, preeclampsia, mirror syndrome, preterm labor, and HELLP syndrome. Significant obstetric complications can be as high as 81%. Intrauterine fetal complications include fetal hydrops from high-output failure, fetal anemia, intratumoral hemorrhage, polyhydramnios, genitourinary obstruction leaking to hydronephrosis and or hydroureter. SCGT size >10 cm or tumor with rapid growth has > 50% perinatal mortality. Tumor characteristics associated with higher mortality rates are early diagnosis, solid components, high vascularity, tumor size > 10 cm, and rapid growth > 150 cm3/week. Another way to risk stratify these patients is by calculating a tumor volume to fetal weight ratio (TFR), which if > 0.12 at < 24 weeks is predictive of an overall poor prognosis. When comparing this case to literature review of sacrococcygeal teratomas, the patient’s fetal SCGT would be classified as high risk of mortality due to the tumor characteristics of early diagnosis, TFR at 20 weeks being 0.16, large size, rapid growth, and pronounced vascularity. Overall, in this high risk case of SCGT, the close follow up and evidence-based management with utilization and collaboration of a multidisciplinary team including Maternal Fetal Medicine, NICU, and Pediatric Surgery in a tertiary center resulted in a successful outcome.