AbstractIntraplacental choriocarcinoma is one of the rarest forms of gestational tumors and is believed to be one of the causes of fetomaternal transfusion (FMT). A 35‐year‐old woman, gravida 2, para 2, with a history of two vaginal deliveries, was incidentally diagnosed as having stage I gestational intraplacental choriocarcinoma with a FIGO/World Health Organization 2000 risk score of 2 after term delivery. This disease caused neonatal anemia but did not metastasize to either the mother or infant. Short tandem repeat analysis with laser microdissection revealed that the tumor had originated from the current pregnancy. Serological test and immunohistochemical analysis revealed that the patient and her baby suffered from FMT. She has been free from disease without any medical intervention for the last 1 year. A combination of multiple biochemical analyses might help us diagnose the precursor pregnancy of a gestational choriocarcinoma and FMT.