Normal second-trimester amniotic fluid alphafetoprotein and acetylcholinesterase associated with fetal sacrococcygeal teratoma.

Amniocentesis was performed at 19 weeks' gestation on a patient with two sequential serum alphafetoprotein values above 2 times median. Ultrasound examination suggested a possible sacrococcygeal teratoma. However, both amniotic fluid alphafetoprotein and acetylcholinesterase were normal, and the patient elected to continue her pregnancy. At 24 weeks fetal demise was confirmed, and prostaglandin induction of labour produced a macerated female fetus with a large sacrococcygeal teratoma.