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Population-based trends in pregnancy hypertension and pre-eclampsia: an international comparative study
  1. Christine L Roberts1,
  2. Jane B Ford1,
  3. Charles S Algert1,
  4. Sussie Antonsen2,
  5. James Chalmers3,
  6. Sven Cnattingius4,
  7. Manjusha Gokhale5,
  8. Milton Kotelchuck5,
  9. Kari K Melve6,
  10. Amanda Langridge7,
  11. Carole Morris3,
  12. Jonathan M Morris1,
  13. Natasha Nassar1,
  14. Jane E Norman8,
  15. John Norrie9,
  16. Henrik Toft Sørensen2,
  17. Robin Walker10,
  18. Christopher J Weir11
  1. 1Perinatal Research, Kolling Institute of Medical Research, University of Sydney, Sydney, New South Wales, Australia
  2. 2Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus N, Denmark
  3. 3Information Services Division, NHS National Services, Edinburgh, UK
  4. 4Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden
  5. 5Maternal and Child Health Department, Boston University School of Public Health, Boston, Massachusetts, USA
  6. 6Medical Birth Registry of Norway, University of Bergen and the National Institute of Public Health, Bergen, Norway
  7. 7Telethon Institute for Child Health Research, Centre for Child Health Research, University of Western Australia, Perth, Western Australia, Australia
  8. 8Tommys Centre for Maternal and Fetal Health, Queen's Medical Research Institute, University of Edinburgh, Edinburgh, UK
  9. 9Robertson Centre for Biostatistics, University of Glasgow, Glasgow, UK
  10. 10Department of Community Health Sciences, University of Calgary, Alberta, Canada
  11. 11Centre for Population Health Sciences, University of Edinburgh Medical School, Edinburgh, UK
  1. Correspondence to Associate Professor Christine Roberts; clroberts{at}


Objective The objective of this study was to compare international trends in pre-eclampsia rates and in overall pregnancy hypertension rates (including gestational hypertension, pre-eclampsia and eclampsia).

Design Population data (from birth and/or hospital records) on all women giving birth were available from Australia (two states), Canada (Alberta), Denmark, Norway, Scotland, Sweden and the USA (Massachusetts) for a minimum of 6 years from 1997 to 2007. All countries used the 10th revision of the International Classification of Diseases, except Massachusetts which used the 9th revision. There were no major changes to the diagnostic criteria or methods of data collection in any country during the study period. Population characteristics as well as rates of pregnancy hypertension and pre-eclampsia were compared.

Results Absolute rates varied across the populations as follows: pregnancy hypertension (3.6% to 9.1%), pre-eclampsia (1.4% to 4.0%) and early-onset pre-eclampsia (0.3% to 0.7%). Pregnancy hypertension and/or pre-eclampsia rates declined over time in most populations. This was unexpected given that factors associated with pregnancy hypertension such as pre-pregnancy obesity and maternal age are generally increasing. However, there was also a downward shift in gestational age with fewer pregnancies reaching 40 weeks.

Conclusion The rate of pregnancy hypertension and pre-eclampsia decreased in northern Europe and Australia from 1997 to 2007, but increased in Massachusetts. The use of a different International Classification of Diseases coding version in Massachusetts may contribute to the difference in trend. Elective delivery prior to the due date is the most likely explanation for the decrease observed in Europe and Australia. Also, the use of interventions that reduce the risk of pregnancy hypertension and/or progression to pre-eclampsia (low-dose aspirin, calcium supplementation and early delivery for mild hypertension) may have contributed to the decline.

  • Trends
  • pregnancy
  • pre-eclampsia
  • gestational hypertension
  • international classification of diseases
  • maternal medicine
  • obstetrics
  • hypertension
  • epidemiology
  • statistics
  • epidmiology
  • delivery
  • birth
  • infant mortality
  • information
  • public health
  • health economics
  • health policy
  • international health services
  • quality in healthcare
  • health and socio-economic inequalities
  • maternal and child health
  • statistics and research methods
  • parturition
  • preterm birth

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  • To cite: Roberts CL, Ford JB, Algert CS, et al. Population-based trends in pregnancy hypertension and pre-eclampsia: an international comparative study. BMJ Open 2011;1:e000101. doi:10.1136/bmjopen-2011-000101

  • Funding The research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors. However, CLR was supported by a NHMRC Senior Research Fellowship (no 457078) and a McKern Travelling Research Scholarship. JBF was supported by NHMRC Capacity Building funding (no 573122), and CJW was supported by the Edinburgh MRC Hub for Trials Methodology Research.

  • Competing interests None.

  • Ethics approval NSW Population and Health Services Research Ethics Committee.

  • Contributors CLR and JBF conceived the project and developed the idea in collaboration with JMM, JC, JEN, JN and CJW. All authors contributed to study design, CLR, JC, SC, MK, KMM, NN, HTS and RW were responsible for data acquisition, and CSA, SA, SC, MG, KKM, AL, CM, RW and CJW contributed to the analysis of data. CLR and JBF initially drafted the manuscript, and all authors were involved in critical revision of the intellectual content. All authors approved the final manuscript.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data sharing statement No additional data available.

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