Epidemiologic data on obstetric and oncologic complications in twin pregnancies combining a complete hydatidiform mole (CHM) coexisting with a normal fetus and placenta are limited.
To evaluate perinatal and obstetric outcomes for mother and fetus and risk of gestational trophoblastic neoplasia (GTN) in twin pregnancies including a CHM.
Pubmed, MEDLINE, and EMBASE and the grey literature were searched for articles published between May 1980 and May 2019 using a protocol designed a priori and registered on PROSPERO (CRD42018112524).
Observational cohort studies of four or more cases confirmed by histopathology and providing data on pregnancy outcomes and GTN.
Two reviewers independently reviewed abstracts and full-text articles. The quality of the studies was assessed with the Newcastle-Ottawa scale and a meta-analysis was performed.
Of the 344 abstracts identified, 14 studies (244 cases) met the eligibility criteria. The incidence of maternal complication in ongoing pregnancies was 80.8% and included vaginal bleeding, hyperthyroidism and pre-eclampsia. There were overall 91 (50%) live-births in ongoing pregnancies and 83 (34%) of the total cases were subsequently diagnosed with GTN. Substantial and significant (p<0.001) heterogeneity was found for the incidence of pre-eclampsia indicating variability in reporting the incidence of some obstetric complications between studies.
Patients diagnosed with a twin pregnancy combining a CHM and an apparently normal fetus have a high risk of perinatal complications, low live birth rates and around a third of them will develop a GTN and should be managed by specialised multidisciplinary teams.

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