Abstract
Birth weight (BW) is a key determinant of infant mortality. Previous studies have reported seasonal fluctuation of BW. However, the responsible environmental factors remain disputable. High-altitude environment provides a great opportunity to test the current hypotheses due to its distinctive climate conditions. We collected BW data of ~ 9000 Tibetan singletons born at Lhasa (elevation: 3660 m) from 2014 to 2018. Using regression models, we analyzed BW seasonality of highland Tibetans. Multivariate models with meteorological factors as independent variables were employed to examine responsible environmental factors accounting for seasonal variation. We compared BW, low-BW prevalence and sex ratio between highland and lowland populations, and we observed a significant seasonal pattern of BW in Tibetans, with a peak in winter and a trough in summer. Notably, there is a marked sex-biased pattern of BW seasonality (more striking in males than in females). Sunlight exposure in the 3rd trimester and barometric pressure exposure in the 2nd trimester are significantly correlated with BW, and the latter can be explained by seasonal change of oxygen partial pressure. In particular, due to the male-biased BW seasonality, we found a more serious BW reduction and higher prevalence of low-BW in males, and a skewed sex ratio in highlanders. The infant BW of highland Tibetans has a clear pattern of seasonality. The winter BW is larger than the summer BW, due to the longer sunlight exposure during the late-trimester. Male infants are more sensitive to hypoxia than female infants during the 2nd trimester, leading to more BW reduction and higher mortality.
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Acknowledgements
We are grateful to all participants and their legal guardians in this study. This work was supported by grants from the National Natural Science Foundation of China (NSFC) (91631306 to B.S; 3217040584 and 32000390 to Y.H.; 32070578 to X.Q and 32170629 to H.Z.), the Youth Innovation Promotion Association of CAS (to Y.H.), the Science and Technology General Program of Yunan Province (202001AT070110 to Y.H.), the Provincial Natural Science Foundation of Tibet Autonomous Region (XZ2018ZRG-130 to J.L.) and Tibetan Fukang Hospital (2017-04 to J.L.).
Funding
This study was funded by grants from the National Natural Science Foundation of China (NSFC) (91631306 to B.S; 3217040584 and 32000390 to Y.H.; 32070578 to X.Q and 32170629 to H.Z.), the Youth Innovation Promotion Association of CAS (to Y.H.), the Science and Technology General Program of Yunnan Province (202001AT070110 to Y.H.), the Provincial Natural Science Foundation of Tibet Autonomous Region (XZ2018ZRG-130 to J.L.) and Tibetan Fukang Hospital (2017–04 to J.L.).
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BS, YH, XQ and Ouzhuluobu conceived the project. XQ, JL, Ouzhuluobu, WZ, YG, HZ, LC, CL, HL and CC collected the data. YH and TY conducted the statistical analysis. YH, BS and XQ wrote the article with inputs from all authors.
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This study was approved by the Internal Review Board of Kunming Institute of Zoology, Chinese Academy of Sciences (Approval ID: SMKX-20160311–45) and the research scheme is in accordance with Regulations of the People's Republic of China on the Administration of Human Genetic Resources.
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He, Y., Li, J., Yue, T. et al. Seasonality and Sex-Biased Fluctuation of Birth Weight in Tibetan Populations. Phenomics 2, 64–71 (2022). https://doi.org/10.1007/s43657-021-00038-7
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DOI: https://doi.org/10.1007/s43657-021-00038-7