Objectives To estimate the incidence of antenatal pulmonary embolism and describe the risk factors, management and outcomes.
Design A national matched case–control study using the UK Obstetric Surveillance System (UKOSS).
Setting All hospitals with consultant-led maternity units in the UK.
Participants A total of 143 women who had an antenatal pulmonary embolism between February 2005 and August 2006. Two hundred and fifty nine matched control women.
Methods Prospective case and control identification through the UKOSS monthly mailing.
Main outcome measures Incidence and case fatality rates with 95% CIs. Adjusted odds ratio estimates.
Results One hundred per cent of UK consultant-led obstetric units contributed data to UKOSS. A total of 143 antenatal pulmonary embolisms were reported, representing an estimated incidence of 1.3 per 10 000 maternities (95% CI 1.1–1.5). Seventy per cent of women had identifiable classical risk factors for thromboembolic disease. The main risk factors for pulmonary embolism were multiparity (adjusted odds ratio [aOR] 4.03, 95% CI 1.60–9.84) and body mass index ≥ 30 kg/m2 (aOR 2.65, 95% CI 1.09–6.45). Nine women who had a pulmonary embolism should have received antenatal thromboprophylaxis with low-molecular-weight heparin (LMWH) according to national guidelines; only three (33%) of them did. Six women (4%) had a pulmonary embolism following antenatal prophylaxis with LMWH; three of these women (50%) were receiving lower than recommended doses. Two women had recurrent pulmonary emboli (1.4%, 95% CI 0.2–5.1%). Five women died (case fatality 3.5%, 95% CI 1.1–8.0%).
Conclusions Significant severe morbidity from thromboembolic disease underlies the maternal deaths from pulmonary embolism in the UK. This study has shown some cases where thromboprophylaxis was not provided according to national guidelines, and there may be scope for further work on guideline implementation.