The diagnosis and prognosis of molar pregnancy: the experience of the National Referral Centre in London.

Since 1973, hCG follow up and treatment of patients with hydatidiform moles in the UK has been centralised. Registrations of moles have increased from 475 to 1248 in 2 years but histological review shows that first trimester non-molar hydropic abortions (HAs) and complete moles (CMs) are often called partial moles (PMs) by pathologists. The introduction and widespread acceptance of the term PM in 1977, coincided with improvements in ultrasound which brought forward 6 weeks the average time of evacuation of CMs, when hydrops is not yet complete but partial and when vessels are present in most CMs, leading to erroneous diagnoses of PM. Many true PMs are dismissed as HAs and often, HAs are called PMs. Valid diagnostic criteria for younger CMs and for PMs have been available for over 10 years and when used, PM is overwhelmingly associated with triploidy. Reported diploid PMs are partly explained by misdiagnosed HAs, rare cases of Beckwith-Widemann syndrome, CMs with partially developed hydrops, twin pregnancies and rare androgenetic CMs with fetal red cells in villi. A rare mole with "normal" diploid biparental karyotype probably exists but morphologically resembles CM. CM and PM have widely different prognosis but the present diagnostic confusion means much of the published epidemiological, clinical and genetic information on PM based on suspect diagnostic criteria ia also suspect.