Development and validation of risk prediction model for venous thromboembolism in postpartum women: multinational cohort study

Alyshah Abdul Sultan, Joe West, Matthew J Grainge, Richard D Riley, Laila J Tata, Olof Stephansson, Kate M Fleming, Catherine Nelson-Piercy, Jonas F Ludvigsson, Alyshah Abdul Sultan, Joe West, Matthew J Grainge, Richard D Riley, Laila J Tata, Olof Stephansson, Kate M Fleming, Catherine Nelson-Piercy, Jonas F Ludvigsson

Abstract

Objective: To develop and validate a risk prediction model for venous thromboembolism in the first six weeks after delivery (early postpartum).

Design: Cohort study.

Setting: Records from England based Clinical Practice Research Datalink (CPRD) linked to Hospital Episode Statistics (HES) and data from Sweden based registry.

Participants: All pregnant women registered with CPRD-HES linked data between 1997 and 2014 and Swedish medical birth registry between 2005 and 2011 with postpartum follow-up.

Main outcome measure: Multivariable logistic regression analysis was used to develop a risk prediction model for postpartum venous thromboembolism based on the English data, which was externally validated in the Swedish data.

Results: 433 353 deliveries were identified in the English cohort and 662 387 in the Swedish cohort. The absolute rate of venous thromboembolism was 7.2 per 10 000 deliveries in the English cohort and 7.9 per 10 000 in the Swedish cohort. Emergency caesarean delivery, stillbirth, varicose veins, pre-eclampsia/eclampsia, postpartum infection, and comorbidities were the strongest predictors of venous thromboembolism in the final multivariable model. Discrimination of the model was similar in both cohorts, with a C statistic above 0.70, with excellent calibration of observed and predicted risks. The model identified more venous thromboembolism events than the existing national English (sensitivity 68% v 63%) and Swedish guidelines (30% v 21%) at similar thresholds.

Conclusion: A new prediction model that quantifies absolute risk of postpartum venous thromboembolism has been developed and externally validated. It is based on clinical variables that are available in many developed countries at the point of delivery and could serve as the basis for real time decisions on obstetric thromboprophylaxis.

Conflict of interest statement

All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declare: funding for the project as described as above; CNP was co-developer of the currently available guidelines on venous thromboembolism prophylaxis in pregnancy issued by the Royal College of Obstetricians and Gynaecologists (green top guideline 37a), has received honorariums for giving lectures from Leo Pharma and Sanofi Aventis (makers of tinzaparin and enoxaparin low molecular weight heparins used in obstetric thromboprophylaxis), and has received payment from Leo Pharma for development of an educational “slide kit” about obstetric thromboprophylaxis; no other relationships or activities that could appear to have influenced the submitted work.

Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.

Figures

https://www.ncbi.nlm.nih.gov/pmc/articles/instance/5137302/bin/sula034245.f1_default.jpg
Fig 1 Assessing calibration in English derivation cohort (top) and Swedish validation cohort (bottom). Intercept was re-estimated for Swedish population on basis of incidence of venous thromboembolism and mean centring all predictors
https://www.ncbi.nlm.nih.gov/pmc/articles/instance/5137302/bin/sula034245.f2_default.jpg
Fig 2 Screenshot of windows based risk prediction program. Based on hypothetical data and coefficients

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