Occupational exertion is associated with a higher risk of preterm delivery, while studies of leisure time activities generally document reduced risks. Less is known about the risk of preterm delivery immediately following episodes of moderate or heavy physical exertion.
We conducted a case–crossover study of 722 women interviewed during their hospital stay for early preterm delivery, defined by a gestational age before 34 weeks, and after 20 weeks. Interviews occurred between March 2013 and December 2015 in seven hospitals in Lima, Peru.
The incidence rate ratio (RR) of early preterm delivery was 5.82-fold higher (95% confidence interval [CI]: 4.29 – 7.36) in the hour following moderate or heavy physical exertion compared to other times and returned to baseline in the hours thereafter. The RR of early preterm delivery within an hour of physical exertion was lower for exertion at moderate intensity (RR=2.43, 95% CI: 1.50 – 3.96) than at heavy intensity (RR=23.62, 95% CI: 15.54 – 35.91, P-homogeneity < 0.001). The RR of early preterm delivery was lower in the hour following moderate physical exertion among women who habitually engaged in physical exertion more than 3 times per week in the year before pregnancy (RR=1.56, 95% CI: 0.81 – 3.00) compared to more sedentary women (RR=6.91, 95% CI: 3.20 – 14.92, P-homogeneity = 0.003).
Our study showed a heightened risk of early preterm delivery in the hour following moderate or heavy physical exertion.
1Department of Epidemiology, Harvard TH Chan School of Public Health, Boston, MA, USA
2Mississauga Academy of Medicine, University of Toronto Mississauga, Mississauga, ON, Canada
3Cardiovascular Epidemiology Research Unit, Beth Israel Deaconess Medical Center, Boston, MA, USA
4Universidad Particular San Martin de Porres, Lima, Peru
5Asociación Civil PROESA, Lima, Peru
6Universidad Peruana Cayetano Heredia, Lima, Peru
7Universidad Peruana de Ciencias Aplicadas, Lima, Peru
8Department of Obstetrics and Gynecology, San Marcos University, Lima, Peru
* These authors contributed equally to this work
Conflicts of interest: None declared
Source of funding: This work was supported by grants R01 HD059827 and T37 MD001449 from the National Institutes of Health.
The data and code are not available for replication because the data are not publicly available.
Acknowledgments: The authors wish to thank the participating hospitals. The authors are indebted to the participants of the PAGE study for their cooperation. They are also grateful to Ms. Elena Sanchez and the dedicated staff members of Asociacion Civil Proyectos en Salud (PROESA), Peru for their expert technical assistance with this research. The authors also thank Ms. Julia Devorak for her help with figure illustration.
Author contributions: MAW, BG, and SES were responsible for study conception and original data collection in Lima, Peru. MAW, BG, and SES contributed to the study design and protocol. SES, JFM, FGM, and PP contributed to the original data collection. HSC conducted the data analysis and drafted the manuscript. HSC, BG, EM, and MAW contributed to data analysis, interpretation and drafting the manuscript. All co-authors (HSC, BG, EM, SES, JFM, FGM, PP, MAW) reviewed the draft manuscript for important intellectual content and provided approval for this final version.
Financial support: This research was supported by awards from the National Institutes of Health (R01 HD059827 and T37 MD001449).
Corresponding author: Harpreet S. Chahal, MSc., Harvard T.H. Chan School of Public Health, Department of Epidemiology, 677 Huntington Avenue, Kresge 500, Boston, MA 02115, Tel: 617-432-1071, Fax: 617-566-7805, Email: firstname.lastname@example.org