Rare heterotopic pregnancy after frozen embryo transfer: a case report and literature review.

<bold>Background: </bold>Heterotopic pregnancy occurred after frozen embryo transfer with two D3 embryos, and the case had a history of bilateral salpingectomy due to salpingocyesis. An ectopic heterotopic pregnancy was implanted in the left psoas major muscle, which has not been previously reported.<bold>Case Presentation: </bold>A 33-year-old woman presented with left back pain after curettage due to foetal arrest in the uterus without vaginal bleeding and spotting, and painkillers relieved the pain initially. When the painkillers ceased to work, the patient returned to the hospital. The β-human chorionic gonadotropin (β-hCG) level remained increased compared with the time of curettage, and a diagnosis of retroperitoneal abdominal pregnancy was suggested by ultrasonography and computerized tomography (CT) with the gestational sac implanted in the left psoas major muscle at the left hilum level. Laparotomy was performed to remove the ectopic pregnancy. During the operation, we carefully separated the adipose tissue between the space of the left kidney door and left psoas major muscle, peeled away the gestational sac that was approximately 50 mm × 40 mm with a 25-mm-long foetal bud, and gave a local injection of 10 mg of methotrexate in the psoas major muscle. Fifty days later, β-hCG decreased to normal levels.<bold>Conclusion: </bold>It is necessary to pay more attention to the main complaints to exclude rare types of ectopic pregnancies of the pelvis and abdomen after embryo transfer. [ABSTRACT FROM AUTHOR]