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Incidence of pulmonary and venous thromboembolism in pregnancies after in vitro fertilisation: cross sectional study

BMJ 2013; 346 doi: (Published 15 January 2013) Cite this as: BMJ 2013;346:e8632
  1. Peter Henriksson, professor1,
  2. Eli Westerlund, physician, PhD student1,
  3. Håkan Wallén, associate professor1,
  4. Lena Brandt, biostatistician2,
  5. Outi Hovatta, professor3,
  6. Anders Ekbom, professor2
  1. 1Division of Cardiovascular Medicine, Department of Clinical Sciences, Danderyd Hospital, Karolinska Institutet, SE 182 88 Stockholm, Sweden
  2. 2Clinical Epidemiology Unit, Department of Medicine, Karolinska Institutet, Sweden
  3. 3Division of Obstetrics and Gynecology, Department of Clinical Science, Intervention and Technology, Karolinska Institutet, Sweden
  1. Correspondence to: P Henriksson peter.henriksson{at}
  • Accepted 14 December 2012


Objective To estimate the risk of pulmonary embolism and venous thromboembolism in pregnant women after in vitro fertilisation.

Design Cross sectional study.

Setting Sweden.

Participants 23 498 women who had given birth after in vitro fertilisation between 1990 and 2008 and 116 960 individually matched women with natural pregnancies.

Main outcome measures Risk of pulmonary embolism and venous thromboembolism (identified by linkage to the Swedish national patient register) during the whole pregnancy and by trimester.

Results Venous thromboembolism occurred in 4.2/1000 women (n=99) after in vitro fertilisation compared with 2.5/1000 (n=291) in women with natural pregnancies (hazard ratio 1.77, 95% confidence interval 1.41 to 2.23). The risk of venous thromboembolism was increased during the whole pregnancy (P<0.001) and differed between the trimesters (P=0.002). The risk was particularly increased during the first trimester, at 1.5/1000 after in vitro fertilisation versus 0.3/1000 (hazard ratio 4.22, 2.46 to 7.26). The proportion of women experiencing pulmonary embolism during the first trimester was 3.0/10 000 after in vitro fertilisation versus 0.4/10 000 (hazard ratio 6.97, 2.21 to 21.96).

Conclusions In vitro fertilisation is associated with an increased risk of pulmonary embolism and venous thromboembolism during the first trimester. The risk of pulmonary embolism is low in absolute terms but because the condition is a leading cause of maternal mortality and clinical suspicion is critical for diagnosis, an awareness of this risk is important.

Trial registration NCT01524393.


  • Contributors: PH, EW, and OH initiated the study. PH and AE had overall responsibility for the study and are the guarantors. All authors contributed to the study design. AE, EW, LB, and PH contributed to data analysis. All authors contributed to the interpretation of the data. PH led the writing of the report and wrote the first draft of the final report. All authors helped to prepare the final report and have seen and approved the final version. The corresponding author had full access to all data in the study and had final responsibility for the decision to submit for publication.

  • Funding: This study was funded through a regional agreement on medical training and clinical research (ALF) between Stockholm County Council and Karolinska Institutet, the Swedish Research Council, and Karolinska Institutet. The sponsors of the study had no role in the study design, data collection, data analysis, data interpretation, or writing of the report. The corresponding author had full access to all the data in the study and had final responsibility for the decision to submit for publication

  • Competing interests: All authors have completed the ICMJE uniform disclosure form at (available on request from the corresponding author) and declare: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; and no other relationships or activities that could appear to have influenced the submitted work.

  • Ethical approval: The study was approved by the research ethics committee of Karolinska Institutet, Stockholm, Sweden (Dnr 2010/267-31/4).

  • Data sharing: No additional data available.

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