Is the incidence of recurrent pregnancy loss increasing? A retrospective register-based study in Sweden.

INTRODUCTION: The aim of this study was to estimate the incidence of recurrent pregnancy loss (RPL). The prevalence of RPL defined as three or more consecutive miscarriages before gestation week 22, is often stated to be 1%. To our knowledge no study has estimated the incidence of RPL, which might be more informative and clinically relevant than the prevalence.

MATERIAL AND METHODS: This retrospective register-based study was conducted from 2003 until 2012 in Sweden with data provided by the Swedish National Board of Health and Welfare. In all, 6852 women were registered with the diagnoses of RPL in the National Patient Register. The incidence of RPL is the number of new women receiving the RPL diagnosis per year in the numerator and population at risk in the denominator.

RESULTS: For each year, from 2003 to 2012, the incidence was calculated in two different risk populations: [1] all women aged 18-42 years, and [2] all women registered as being pregnant (deliveries or miscarriages). The average incidence in the study period was 53 per 100 000 (0.05%) in women aged 18-42 years and 650 per 100 000 (0.65%) in women who had achieved pregnancy in the period. The incidence of RPL in the two risk populations increased by 74 and 58%, respectively, during the study period.

CONCLUSION: This study suggests that the incidence of RPL increased during the 10-year period studied. Causes can only be speculated upon in this study design, but might be associated with environmental changes, as the increase was fairly rapid.