Seasonality in Birth Weight: Review of Global Patterns and
Gabriel Chodick,1,2 Shira Flash,1,3 Yonit Deoitch,2 and Varda Shalev1,2
Abstract Birth weight is the single most significant determinant of infant
mortality and the chances of a newborn to experience healthy development.
Low birth weight also appears to be related to higher risks of several im-
portant chronic conditions, such as ischemic heart disease, non-insulin-
dependent diabetes, and cancer in adults. Thus factors that influence in utero
growth and birth weight may have a serious effect on health outcomes many
years later in life. Analysis of seasonal variations in birth weights may en-
able us to suggest specific factors that influence this measure. In this review
we summarize the literature on seasonal variations in birth weight. Although
causes of seasonal variation in developing regions are more clearly under-
stood, it is not yet clear which factors affect apparent seasonal variation in
birth weight in developed countries. In our analysis we observed a pattern
of seasonal variations in developed countries that differed between low-,
middle-, and high-latitude countries, and we suggest several mechanisms
that may be responsible for this diversity. Namely, we suggest that in middle-
latitude climates, the large annual temperature range may cause low birth
weights during summer, whereas in high- and low-latitude regions variations
in sunlight exposure between seasons may contribute to low birth weights
apparent during winter. Identification of the suggested causal environmental
factors may have public health implications in the development of primary
prevention programs for low birth weight and macrosomia in developed
Birth weight is a key measure that influences infant morbidity, mortality, and
growth rate throughout childhood and adulthood (Kramer 1987; Wilcox 2001),
presenting a complex interplay between biological, social, and psychological fac-
tors (Spencer 2003). In utero development is influenced by a complex matrix of
genetic and epigenetic factors operating on the maternal-fetal unit, and it is also
related to higher risks of chronic disease, such as ischemic heart disease (Frankel
et al. 1996; Leon et al. 1998), non-insulin-dependent diabetes (Forsen et al. 2000),
Maccabi Institute for Healthcare Research, Tel Aviv, Israel.
School of Public Health, Tel Aviv University, Tel Aviv, Israel.
Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
Human Biology, August 2009, v. 81, no. 4, pp. 463–477.
Copyright © 2009 Wayne State University Press, Detroit, Michigan 48201-1309
Key words: seasonality, birth weight, pregnancy, geographic