Role of maternal age and pregnancy history in risk of miscarriage: prospective register based studyBMJ 2019; 364 doi: https://doi.org/10.1136/bmj.l869 (Published 20 March 2019) Cite this as: BMJ 2019;364:l869
- Maria C Magnus, researcher123,
- Allen J Wilcox, senior investigator14,
- Nils-Halvdan Morken, senior consultant156,
- Clarice R Weinberg, senior investigator7,
- Siri E Håberg, deputy director1
- 1Centre for Fertility and Health, Norwegian Institute of Public Health, PO Box 222 Skøyen, N-0213 Oslo, Norway
- 2MRC Integrative Epidemiology Unit at the University of Bristol, Bristol, UK
- 3Department of Population Health Sciences, Bristol Medical School, Bristol, UK
- 4Epidemiology Branch, National Institute of Environmental Health Sciences, Durham, NC, USA
- 5Department of Clinical Science, University of Bergen, Bergen, Norway
- 6Department of Obstetrics and Gynecology, Haukeland University Hospital, Bergen, Norway
- 7Biostatistics and Computational Biology Branch, National Institute of Environmental Health Sciences, Durham, NC, USA
- Correspondence to: M C Magnus
- Accepted 11 February 2019
Objectives To estimate the burden of miscarriage in the Norwegian population and to evaluate the associations with maternal age and pregnancy history.
Design Prospective register based study.
Setting Medical Birth Register of Norway, the Norwegian Patient Register, and the induced abortion register.
Participants All Norwegian women that were pregnant between 2009-13.
Main outcome measure Risk of miscarriage according to the woman’s age and pregnancy history estimated by logistic regression.
Results There were 421 201 pregnancies during the study period. The risk of miscarriage was lowest in women aged 25-29 (10%), and rose rapidly after age 30, reaching 53% in women aged 45 and over. There was a strong recurrence risk of miscarriage, with age adjusted odds ratios of 1.54 (95% confidence interval 1.48 to 1.60) after one miscarriage, 2.21 (2.03 to 2.41) after two, and 3.97 (3.29 to 4.78) after three consecutive miscarriages. The risk of miscarriage was modestly increased if the previous birth ended in a preterm delivery (adjusted odds ratio 1.22, 95% confidence interval 1.12 to 1.29), stillbirth (1.30, 1.11 to 1.53), caesarean section (1.16, 1.12 to 1.21), or if the woman had gestational diabetes in the previous pregnancy (1.19, 1.05 to 1.36). The risk of miscarriage was slightly higher in women who themselves had been small for gestational age (1.08, 1.04 to 1.13).
Conclusions The risk of miscarriage varies greatly with maternal age, shows a strong pattern of recurrence, and is also increased after some adverse pregnancy outcomes. Miscarriage and other pregnancy complications might share underlying causes, which could be biological conditions or unmeasured common risk factors.
Contributors: MCM, AJW, and SEH conceived and designed the study. SEH obtained access to data. MCM conducted the data analysis and drafted the initial version of the manuscript. CRW and NHM provided important insight during the data analysis. All authors contributed in the interpretation of the data and critically revised the manuscript. All authors had full access to the data in the study and can take responsibility for the integrity of the data and the accuracy of the data analysis. MCM is the guarantor. The corresponding author attests that all listed authors meet authorship criteria and that no others meeting the criteria have been omitted.
Funding: This research was supported by the Research Council of Norway through its Centres of Excellence funding scheme, project number 262700. The work was also supported by the Intramural Program of the National Institute of Environmental Health Sciences, NIH (AJW and CRW). MCM works at the Medical Research Council (MRC) Integrative Epidemiology Unit at the University of Bristol which receives infrastructure funding from the UK MRC (MC_UU_00011/6), and she is also supported by a fellowship from the UK MRC (MR/M009351/1). The funders had no role in the completion of the research project, the writing of the manuscript for publication, or the decision to publish the results.
Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf 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; no other relationships or activities that could appear to have influenced the submitted work.
Ethical approval: The national register linkage was approved by the Regional Committee for Medical and Health Research Ethics for South/East Norway (2014/404).
Data sharing: No additional data are available.
The lead author (MCM) affirms that the manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned have been explained.
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