A rapidly growing fetal teratoma

In June, 1996, a 25-year-old woman was referred for assessment of a fetus (25 weeks' gestation) with a sacrococcygeal teratoma. The teratoma was first detected on a routine 20-week ultrasound scan. The tumour grew rapidly thereafter to become nearly the size of the fetus. By 25 weeks, polyhydramnios and placentomegaly had developed. Fetal echocardiography showed that a large portion of the fetal cardiac output perfused the teratoma. Placental thickness increased from 40 mm to 60 mm (normal 25 mm) in 1 week, and maternal tachycardia and proteinuria suggested impending maternal mirror syndrome.