Complete Molar Pregnancies with a Coexisting Fetus: Pregnancy Outcomes and Review of Literature.

 The objective of the study was to review the obstetric outcomes of complete hydatidiform molar pregnancies with a coexisting fetus (CHMCF), a rare clinical entity that is not well described.  We performed a retrospective case series with pathology-confirmed HMCF. The cases were collected via solicitation through a private maternal-fetal medicine physician group on social media. Each contributing institution from across the United States (  = 9) obtained written informed consent from the patients directly, obtained institutional data transfer agreements as required, and transmitted the data using a Health Insurance Portability and Accountability Act of 1996 (HIPAA) compliant modality. Data collected included maternal, fetal/genetic, placental, and delivery characteristics. For descriptive analysis, continuous variables were reported as median with standard deviation and range.  Nine institutions contributed to the 14 cases collected. Nine (64%) cases of CHMCF were a product of assisted reproductive technology and one case was trizygotic. The median gestational age at diagnosis was 12 weeks and 2 days (9 weeks-19 weeks and 4 days), and over half were diagnosed in the first trimester. The median human chorionic gonadotropin (hCG) at diagnosis was 355,494 mIU/mL (49,770-700,486 mIU/mL). Placental mass size universally enlarged over the surveillance period. When invasive testing was performed, insufficient sample or no growth was noted in 40% of the sampled cases. Antenatal complications occurred in all delivered patients, with postpartum hemorrhage (71%) and hypertensive disorders of pregnancy (29%) being the most frequent outcomes. Delivery outcomes were variable. Four patients developed gestational trophoblastic neoplasia.  This series is the largest report of obstetric outcomes for CHMCF to date and highlights the need to counsel patients about the severe maternal and fetal complications in continuing pregnancies, including progression to gestational trophoblastic neoplastic disease. CHMCF is a rare obstetric complication and may be associated with the use of assisted reproductive technology.Universally, patients with CHMCF who elected to manage expectantly developed antenatal complications.The risk of developing gestational trophoblastic neoplasia after CHMCF is high, and termination of the pregnancy did not decrease this risk.