Seasonal inconstancy of human sex ratio at birth

Melnikov, V. N.

doi:10.1016/j.earlhumdev.2015.10.008

Cited by 10 publications

(4 citation statements)

References 40 publications

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“…However, the father's season of birth did not affect the sex ratio of the offspring suggesting that the effect is related to a maternal birth seasonal mechanism 46 . Others have shown that there is seasonality in the sex ratio of children born in Russia however, the authors did not investigate the relationship between maternal birth season and sex ratio 47 .…”

Section: Maternal Birth Season Determines Characteristics Of Offsprinmentioning

confidence: 96%

Female Reproductive Performance and Maternal Birth Month: A Comprehensive Meta-Analysis Exploring Multiple Seasonal Mechanisms

Boland

Fieder²,

John

et al. 2020

Sci Rep

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Globally, maternal birth season affects fertility later in life. The purpose of this systematic literature review is to comprehensively investigate the birth season and female fertility relationship. Using PubMed, we identified a set of 282 relevant fertility/birth season papers published between 1972 and 2018. We screened all 282 studies and removed 131 non-mammalian species studies on fertility and 122 studies that were on non-human mammals. Our meta-analysis focused on the remaining 29 human studies, including twelve human datasets from around the world (USA, Europe, Asia). The main outcome was change in female fertility as observed by maternal birth month and whether this change was correlated with either temperature or rainfall. We found that temperature was either strongly correlated or anti-correlated in studies, indicating that another factor closely tied to temperature may be the culprit exposure. We found that rainfall only increases fertility in higher altitude locations (New Zealand, Romania, and Northern Vietnam). This suggests the possibility of a combined or multi-factorial mechanism underlying the female fertility-birth season relationship. We discuss other environmental and sociological factors on the birth season-female fertility relationship. Future research should focus on the role of birth season and female fertility adjusting for additional factors that modulate female fertility as discussed in this comprehensive review. Over 12% of reproductive age women (15-44 years) in the United States of America suffer from infertility or impaired fecundity 1 , with some estimates as high as 16% 2. European countries show similarly high infertility rates with Great Britain at 17% 3. In developing countries, the rate of infertility is estimated at 1 in 4 couples 4,5. In addition to rising infertility rates among humans, increases in infertility and reproductive disorders were observed in dairy cows 6. Dairy researchers found that a cool, low-temperature, environment appeared to preserve fertility and reduce the risk of reproductive disorders 6 furthering support for a relationship between temperature and female fertility. Although at least one study points to other factors besides temperature that play a role more significant role at the country-level on female fertility 7. Maternal birth season effects female fertility outcomes 8 , including in both hunter/gather societies (e.g., Hiwi of Venezuela) 9 and industrialized societies 8,10. Birth season can affect later risk of disease through alterations in the prenatal environment that alter growth patterns and processes 11. In addition, the known relationship between temperature and fertility 6 could also manifest itself in a birth season relationship. The main biological mechanism underlying a birth season relationship with female fertility remains the hypothesis that oocytes' exposure to high temperatures at birth and shortly thereafter results in increased oocyte

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Section: Maternal Birth Season Determines Characteristics Of Offsprinmentioning

confidence: 96%

Female Reproductive Performance and Maternal Birth Month: A Comprehensive Meta-Analysis Exploring Multiple Seasonal Mechanisms

Boland

Fieder²,

John

et al. 2020

Sci Rep

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“…In humans, male births exceed female births and this ratio is conventionally referred to M/F, denoting male births divided by total births. M/F may be influenced by a large number of factors (1) and has been shown to exhibit seasonal variation in various parts of the world (2).…”

Section: Introductionmentioning

confidence: 99%

Racial Differences in Seasonal Variation in Election and Non-election Years in the Male to Female Ratio at Birth in the United States

Grech¹,

Borg²

2016

West Indian Med J

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“…This convention will be used in this paper. A wide variety of factors have been shown to influence the sex ratio at birth (SR), and these include secular and geographical variation (Pavic, 2015), as well as seasonal trends (Melnikov, 2015). However, toxins, including exogenous chemicals (James, 1987), as well as endogenous hormones produced by stress, invariably lower the sex ratio at birth (James, 2004).…”

Section: Introductionmentioning

confidence: 99%

Effects of Stressful Events in France (1968) and Japan (1995) on the Sex Ratio at Birth

2016

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Males are usually born in excess of females. The sex ratio at birth (SR) is often expressed as the ratio of male to total births. A wide variety of factors have been shown to influence SR, including terrorist attacks, which have been shown to reduce SR. This paper reviews the effects on SR outcomes of the stressful events in France in 1968 (in association with the student and worker riots) and in Japan following the Aum Shinrikyo religious cult's attack on the Tokyo subway using sarin nerve gas in 1995. Both countries displayed seasonal variation in SR. France exhibited a decline in SR in 1968 (p=0.042), with a particularly strong dip in May of that year (p=0.015). For Japan, there was no statistically significant dip for 1995 but there was a significant dip in June of that year (p=0.026). The SR dips follow catastrophic or tragic events if these are perceived to be momentous enough by a given populace. It is believed that SR slumps may be caused by population stress, which is known to lead to the culling of frail/small male fetuses. It has been observed that these fluctuations are comparable in intensity to a substantial proportion of quoted values for perinatal mortality, potentially making this a public health issue.

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Seasonal inconstancy of human sex ratio at birth

Cited by 10 publications

References 40 publications

Female Reproductive Performance and Maternal Birth Month: A Comprehensive Meta-Analysis Exploring Multiple Seasonal Mechanisms

Female Reproductive Performance and Maternal Birth Month: A Comprehensive Meta-Analysis Exploring Multiple Seasonal Mechanisms

Racial Differences in Seasonal Variation in Election and Non-election Years in the Male to Female Ratio at Birth in the United States

Effects of Stressful Events in France (1968) and Japan (1995) on the Sex Ratio at Birth

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