Abstract
Incidences of hydatidiform mole (HM) registered in European countries varies from 0.98/1000 to 2.17/1000 deliveries, while higher incidences have been reported in other parts of the world. We calculated the incidence by selecting data on HMs classified as ”first”, “second” and “third” from 01.01.1999 to 31.12.2014 registered in the Danish Pathology Registry, which we previously showed to be the most complete data source on the number of HMs in Denmark. In the study period, 1976 first HMs were registered; 1080 (55%) were classified as PHMs (partial HMs) and 896 (45%) as NPHMs (HMs not registered as PHMs). The average incidence of HM was 1.98/1000 deliveries. The incidence of PHM was 1.08/1000 deliveries and the incidence of NPHM was 0.90/1000 deliveries. Forty HMs were registered as second HMs; 85% (34/40) were of the same histopathological type as the first HM. The registered incidence of HM decreased from 2.55/1000 deliveries in 1999 to 1.61/1000 deliveries in 2014 (p < 0.005). The decrease in the incidence of HM was identical with a decrease in the incidence of PHM. New medical practices such as medical abortion and only forwarding selected pregnancy products for histopathologic examination may cause a declining number of HMs registered.
Highlights
Several factors limit the accuracy of the incidences estimated
Women with a hydatidiform mole (HM) are registered in three governmental registries: the Danish National Patient R egistry[13], the Danish Cancer R egistry[14], and the Danish Pathology Registry (DPR)[15]
To identify incidences of HM reported from population-based studies, we identified literature in PubMed by searching for “molar pregnanc*” or “hydatidiform” or “gestational trophoblastic disease*” in the title, and “incidence*” in the title or abstract, for papers published in the period 01.01.1999–31.12.2019
Summary
Several factors limit the accuracy of the incidences estimated. First and foremost, we know little about very early pregnancies. We do not know the correct denominator, as the total number of pregnancies in a population can only be estimated with uncertainty. The accuracy of the incidences estimated will be influenced by other factors, such as the ability to uniquely identify each individual in a population and the completeness of the registries used. In Denmark, each individual is unambiguously identifiable due to the civil personal registration (CPR) number, assigned at birth or immigration. Systematic registration of births in Denmark started in 1 96812, and since 2006 the number of induced abortions and miscarriages has been registered in the Danish Database for Early Pregnancy and Abortion (TiGrAb, se description below). We present the incidence of HM in Denmark for the period 1999–2014, estimated from data in the DPR. We observed a significantly decreasing incidence of PHM over time
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