Mortality from venous thromboembolism in young Swedish women and its relation to pregnancy and use of oral contraceptives – an approach to specifying rates

Abstract

Pregnancy and use of combined oral contraceptives (COCs) are major risk factors for venous thromboembolism (VTE) in young women and we wanted to obtain accurate VTE mortality data overall, by age, associated with the use of COCs and pregnancy. From the Swedish Cause of Death Register (CDR) we identified women aged 15-44 with VTE as underlying or contributory cause of death during the period 1990-1999. We scrutinized medical records and included verified VTE cases without active cancer or terminal disease. Pregnancy statistics and COC utilization data were obtained from national databases. Of the 120 cases included, 9 (8%) were associated with pregnancy and 28 (23%) with current COC use. The overall refined VTE mortality rate in current COC users was 7.5[4.7; 10.3] per million user-years and the corresponding pregnancy-related rate was 8.9[4.1;17.0] per million pregnancy years, rates increasing with age. For ages 15-24, the rate was significantly higher in current COC users than in non-pregnant women not using COCs: 6.0[3.1; 10.5] per million user-years vs. 0.3[0.0; 1.2] per million woman years. Underlying cause mortality data included 82% of VTE deaths associated with COCs, and 56% of maternal deaths had a pregnancy-related code. Mortality figures from VTE associated with the use of COCs and pregnancy were similar. COC use had an important impact on the total VTE mortality in the youngest age group. Standard mortality statistics do not allow accurate monitoring of VTE mortality in young women due to missing data, misdiagnoses and coding rules.