Summary
In an attempt to reduce the incidence of pregnancy associated venous thromboembolism
(PA-VTE), some researchers have advocated screening of all women for the factor VLeiden mutation during early pregnancy. We have conducted a large retrospective study (over
72,000 deliveries) to determine if this would be useful. Sixty-two objectively confirmed
venous thrombotic events (51 DVT, 11 PE) were recorded at two maternity units in the
UK. The incidence of DVT was 0.71 per 1000 deliveries (95% CI 0.5-0.9) with 0.50 occurring
in the antenatal period (95% CI 0.34-0.66) and 0.21 in the puerperium (95% CI 0.11-0.31).
The incidence of PE was 0.15 per 1000 deliveries (95% CI 0.06-0.24), 0.07 antenatal
(95% CI 0.01-0.13) and 0.08 in the puerperium (95% CI 0.02-0.14). Of these 62,50 attended
for follow-up and thrombophilia screening. 28% of all episodes of PA-VTE had no CIinical
risk factor for thrombosis or an identifiable thrombophilic abnormality. Deficiency
of antithrombin was identified in 12% of individuals (95% CI 3-21) and the factor
VLeiden mutation in 8% (95% CI 0.5-15.5). Based on estimates of the prevalence of the factor
VLeiden mutation in the population, we estimate that the thrombotic risk for a woman during
pregnancy or the puerperium with the defect is approximately 1 in 400-500. This figure
would not lend support to the idea of random screening for the mutation in early pregnancy.
