National register data are of value in studies on miscarriage-Validation of the healthcare register data in Finland

Introduction Despite the high prevalence of miscarriages, they are not systematically registered and few epidemiological studies have been done. As Finnish health registries are comprehensive and widely used in research, we validated the Finnish register data concerning diagnostics and treatment of miscarriage, and treatment-related adverse events. Material and methods We conducted a validation study regarding miscarriage-related codes of diagnoses and surgical procedures in a Finnish National Hospital Discharge Registry (NHDR) by comparing the information from the NHDR with that of the hospital records. We selected a random sample of 4 months during 1998-2016 from three hospitals, comprising 687 women aged 15-49 experiencing a first miscarriage during follow-up. Women with diagnoses unrelated to miscarriage, or proven to be other than miscarriage, were excluded. The final sample consisted of 643 women with confirmed miscarriage, which was used for analyses regarding the diagnosis, treatment and adverse events of miscarriage treatment. Results The majority of miscarriages registered in the NHDR were confirmed by the hospital records (positive predictive value [PPV] = 93.6% [95% confidence interval [CI] 91.8%-95.4%]). Different types of miscarriage were also reliably identified; spontaneous abortion with PPV = 85.6% (95% CI 80.9%-89.2%), missed abortion with PPV = 92.7% (95% CI 88.8%-95.3%) and blighted ovum with PPV = 91.1% (95% CI 84.3%-95.1%). The PPV of surgical treatment (62.2% [95% CI 55.7%-68.3%]) was lower than the PPV of non-surgical treatment (93.3% [95% CI 90.5%-95.3%]). The diagnoses regarding adverse events of miscarriage treatment could be reliably identified. The PPV for clinical infections was 76.0% (95% CI 56.6%-88.5%) and for retained products of conception or/and vaginal bleeding 96.8% (95% CI 83.8%-99.4%). Conclusions The coverage of the NHDR was good concerning identification of miscarriages, different types of miscarriages and non-surgical treatment. Nevertheless, there is a need for clearly defined procedural codes concerning to medical treatment of miscarriage. The register-based data are reliable and practicable for both clinical evaluation and research concerning miscarriage.