Month of birth and offspring count of women: data from the Southern hemisphere

BACKGROUND Several studies indicate that the month of birth affects later reproductive output of women in the Northern hemisphere. METHODS To investigate whether a comparable but time-shifted effect is also present in the Southern hemisphere where the seasonal variation of the environment is reverse...

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Bibliographic Details
Published in:Human reproduction (Oxford) 2008-05, Vol.23 (5), p.1187-1192
Main Authors: Huber, S., Didham, R., Fieder, M.
Format: Article
Language:English
Subjects:
Adult
Aged
Biological and medical sciences
birth date
European Continental Ancestry Group
Female
Fertility
Gynecology. Andrology. Obstetrics
hemisphere
Humans
Medical sciences
Middle Aged
New Zealand
Parturition
reproduction
season
Seasons
Socioeconomic Factors
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Summary:BACKGROUND Several studies indicate that the month of birth affects later reproductive output of women in the Northern hemisphere. METHODS To investigate whether a comparable but time-shifted effect is also present in the Southern hemisphere where the seasonal variation of the environment is reversed, we analysed the association between birth month and offspring count in post-reproductive New Zealand women. We further examined whether this association differed with the hemisphere of birth as well as the socio-economic background. RESULTS We find that the association between birth month and offspring count of New Zealand women born in the Southern, albeit not Northern, hemisphere is a mirror image of the pattern reported from Austrian women: on average, women born during the Southern hemisphere summer months have fewer children than women born in winter. This association is highly significant within the lowest family income category but insignificant within higher family income categories. CONCLUSIONS This study provides evidence for a causal link between the seasonality of the environment during the pre- and perinatal period and offspring count of women. It further indicates that the main contribution of the birth month effect found in the present study comes from the lowest family income category.
ISSN:0268-1161
1460-2350
DOI:10.1093/humrep/den079