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Low risk of pulmonary embolism in pregnancy

Obstetrics and gynaecology

Obstetrics and gynaecology

The incidence of pulmonary embolism?(PE) during pregnancy is one case per 7,700 pregnancies, a study has found.

The study collected data on PE in pregnancy over an 18-month period from all UK obstetric units. It identified 143 cases, which were compared with 259 matched controls. The median gestational age at diagnosis was 28 weeks, with the greatest risk between 32 and 36 weeks.

Classic risk factors were identified in 70% of cases and 49% of controls. Only two risk factors were found to occur more significantly in the case group: a BMI >30kg/m2 (OR 2.65, 95% CI 1.09-6.45) and multiparity (OR 4.03, 95% CI 1.6-9.84). There was a suggestion that risk increased.

with BMI, although the authors could not investigate subgroups of women with a BMI?greater than 30 because the number of cases was not sufficient. The odds ratio did not differ significantly between women who had had one previous delivery and those who had had two or more previous deliveries.

Non-significant trends toward increased risk were observed in women with a recent history of long-haul air travel or a family history of venous thromboembolism. Maternal age and surgery during pregnancy were not associated with elevated risk, possibly because of insufficient case numbers.

The overall incidence of PE was just one case per 7,700 pregnancies. Under current UK?guidelines, 94% of cases were not eligible for prophylaxis with a low molecular weight heparin. However, if the guideline threshold for prophylaxis was lowered from three risk factors to two risk factors, just

13 more cases would have received prophylaxis and heparin would have been offered to 102,000 other women (9% of all maternities).

Three deaths occurred among the 143 cases, one in the first trimester and two in the third.

The Confidential Enquiry into Maternal and Child Health, one of the most respected and long running medical audits in the UK, has already established that pulmonary embolism is the most important cause of direct maternal mortality.

However, while PE in pregnancy is highly significant and potentially life threatening, these epidemiological data suggest that the absolute risks in the UK are low and that prospective identification of those at risk is, at best, very imprecise.

For prophylaxis to be effective, vast numbers of women would need to accept the benefits and, significantly, risks of anticoagulation. The fact that just 10 of the 143 cases of PE in this study occurred in women with a known DVT suggests that we all need to maintain a high index of clinical suspicion in women who are pregnant.

Knight M; UKOSS. Antenatal pulmonary embolism:?risk factors, management and outcomes. BJOG 2008;115:453-61


Dr Chris Barclay
GP, Sheffield

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