Postpartum Venous Thromboembolic Events Among Carriers of Factor V Leiden and/or Prothrombin Gene Variant: A Cohort Study and Updated Systematic Review. Is Prophylaxis Really Required?
Authors: Lapner Sarah Louise Dunbar Takach , Le Gal Gregoire , Le Templier Genevieve , Walker Mark , Smith Graeme N , Wells Phil , Ramsay Timothy , Langlois Nicole , Carson Nancy , Wen Shi Wu , Rodger Marc A. 
Published: October 2019

Abstract
Abstract 1142

Background
Pregnancy is associated with a hypercoagulable state, with the highest risk of venous thromboembolism (VTE) occurring during the postpartum period. This risk is further increased by the presence of inherited thrombophilic states, including Factor V Leiden (FVL) or the prothrombin gene variant (PGV), such that many clinicians provide routine postpartum thromboprophylaxis for this group. Publications examining the absolute incidence of pregnancy associated VTE in carriers of FVL and PGV report a rate of only 0–1% over the combined antepartum and 6–12 week postpartum periods. However, given that at least 50% of pregnancy associated VTE occur postpartum, the daily risk of VTE may be sufficiently high to warrant thromboprophylaxis during this period.

Objectives

Methods
We performed a substudy analysis of the prospective Ottawa and Kingston (OaK) birth cohort study, in which women presenting for routine antenatal care were followed throughout pregnancy until delivery. Genotyping for FVL and PGV by polymerase chain reaction was performed for all participants after completion of the postpartum period. 336 women who enrolled through the participating Ottawa hospitals and identified as FVL or PGV positive were eligible for the current analysis. Data relating to the occurrence of VTE during the 6-week post partum period were obtained for 201/336 women through medical record review or direct contact by a study investigator. The main outcome measure was the proportion of objectively confirmed VTE within 6 weeks of delivery among participants with heterozygous FVL or PGV.
Eligible articles were identified through a comprehensive search of the MEDLINE database. Inclusion criteria included a) prospective cohort design of women completing pregnancy during the study period; b) assessment of all participants for FVL and/or PGV; c) observation of participants throughout the postpartum period; d) report of objectively confirmed VTE during the postpartum period. Studies limited to women with previous pregnancy complications or previous VTE were excluded. The pooled proportion of postpartum VTE was calculated from combination of reported postpartum VTE rates and the current study results.

Results
No postpartum VTE occurred among the 188 participants heterozygous for FVL or PGV alone. The proportion of VTE among the population with isolated heterozygous FVL and/or PGV was 0% (95% CI 0 to 2.0). One postpartum event was documented in a heterozygous PGV carrier with coexisting protein C deficiency. No events were documented among 12 women with homozygous or compound heterozygous defects. Superficial vein thrombosis was diagnosed in two carriers of FVL.
Ten publications examining the rate of postpartum VTE among FVL or PGV carriers were identified in the systematic review. (Table 1) The pooled proportion of postpartum VTE among those who did not receive postpartum prophylaxis was 0.6% (95% CI 0.2 to 1.3) for heterozygous carriers of FVL and 0% (95% CI 0 to 1.6) for PGV heterozygotes.

Conclusion
The absolute risk of VTE among asymptomatic carriers of FVL or PGV appears sufficiently low to withhold postpartum prophylaxis.

Disclosures:
Ramsay: Heart and Stroke Foundation of Canada: Research Funding; Canadian Institutes of Health Research: Research Funding. Rodger:Canadian Institutes of Health Research: Research Funding; Heart and Stroke Foundation of Canada: Research Funding.