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Effect of Month of Birth on Mean Birth Length in Austrian Newborns Born Between 1984 and 2021

Waldhoer, T., Kirchengast, S., Yang, L., 2024. Effect of Month of Birth on Mean Birth Length in Austrian Newborns Born Between 1984 and 2021. American Journal of Human Biology 36, e24146.

Introduction

The fetal growth process and consequently birth length is not only the result of genetic and epigenetic factors but are also largely influenced by environmental conditions (Jamshed et al. 2020; Mariet et al. 2021; Rollin 2022). Particular attention is paid to seasonal variations in newborn size, which are associated with climatic factors, temperature, and sunlight exposure (McGrath et al. 2005; Rashid et al. 2017; Leung et al. 2023), although findings on patterns of seasonal fluctuations in newborn size are inconsistent. Dimitrova et al. (2023) describe the longest birth lengths for Bulgaria during winter and the shortest during the summer months, while Wohlfahrt et al. (1998) observed the largest birth lengths in a Danish sample in April. In an Australian sample, a peak in limb length occurred for those born in winter and spring (McGrath et al. 2005). Reduced fetal growth and therefore smaller newborn size is often described at elevated external temperatures during late pregnancy (Chodick et al. 2009; Sun et al. 2019). However, larger birth lengths have also been associated with increased temperatures in the last month of pregnancy (Rashid et al. 2017).

The aim of the present descriptive study focusing on the birth length of Austrian newborns is to analyze seasonal fluctuations by month of birth and additionally evaluate temporal changes in monthly fluctuations across birth cohorts spanning from 1984 to 2021. Based on the results of the most recent study by Dimitrova et al. (2023), we hypothesize longest birth lengths during the winter months.

 

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