Abstract
Background
Fetal malpresentation, such as breech, transverse, and oblique presentations, is a frequent diagnosis in obstetrical practice. While several maternal factors have been studied, the potential relationship between maternal sedentary behavior and fetal malpresentation remains underexplored. This study aimed to examine the association between sedentary behavior during pregnancy and fetal malpresentation using data from a large longitudinal cohort study conducted in Japan.
Methods
This prospective longitudinal cohort study recruited approximately 100,000 pregnant women from 15 Regional Centers in Japan. Participants completed self-administered questionnaires in the first and either the second or third trimester of pregnancy. Sedentary behavior was defined as the number of hours spent sitting or lying down per day. The fetal presentation at delivery was recorded from medical records. Logistic regression analyses were conducted to estimate the odds ratio of the association between sedentary time and the likelihood of fetal malpresentation.
Results
Here we show that among 73,813 eligible participants, the mean maternal age is 31.3 years, 27.4% deliver at ≥35, 3.0% experience fetal malpresentation, and 48.7% have female infant. The median sedentary time is 5 hours (interquartile range: 3–8). Women who report ≥12 hours sedentary time per day have higher odds for fetal malpresentation compared to those reporting <6 hours (adjusted odds ratio: 1.17; 95% confidence interval: 1.02–1.35).
Conclusions
The findings emphasize the need to address sedentary behavior as a modifiable risk factor during pregnancy, which may implicate future interventions aimed at reducing the incidence of fetal malpresentation.
Plain language summary
Fetal malpresentation is a frequent diagnosis in pregnancy where the fetus is positioned incorrectly in the womb. We examined the association between time sitting or lying down during pregnancy and fetal malpresentation. Approximately 100,000 pregnant women completed self-administered questionnaires in the first and either the second or third trimester of pregnancy. The median sitting or lying time was 5 hours. Women who reported more than 12 hours per day had higher odds for fetal malpresentation compared to those reporting less than 6 hours. The findings emphasize the need to address sedentary behavior as a modifiable risk factor during pregnancy, which may improve treatments aimed at reducing the incidence of fetal malpresentation.
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Acknowledgements
We would like to express our gratitude to all the study participants and the individuals involved in the data collection. This study was funded by the Ministry of the Environment, Japan. The findings and conclusions of this article are solely the responsibility of the authors and do not represent the official views of the above government.
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Kikuchi, K., Michikawa, T., Morokuma, S. et al. Sedentary time during pregnancy and fetal malpresentation in the Japan Environment and Children’s Study. Commun Med (2026). https://doi.org/10.1038/s43856-026-01635-1
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DOI: https://doi.org/10.1038/s43856-026-01635-1
