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THE INFLUENCE OF BIRTH ORDER ON BIRTH WEIGHT: DOES THE SEX OF PRECEDING SIBLINGS MATTER?

Published online by Cambridge University Press:  07 August 2003

KARINE CÔTÉ
Affiliation:
Centre for Addiction and Mental Health and University of Toronto, Toronto, Canada
RAY BLANCHARD
Affiliation:
Centre for Addiction and Mental Health and University of Toronto, Toronto, Canada
MARTIN L. LALUMIÈRE
Affiliation:
Centre for Addiction and Mental Health and University of Toronto, Toronto, Canada

Abstract

The purpose of this study was to investigate whether the well-established relationship between parity and birth weight is affected by the sex composition of siblings, especially for male newborns. Subjects were 856 male and 862 female newborns who weighed at least 2500 g at birth, who were born after 37 completed weeks of gestation, who obtained an Apgar score of 7 or higher, who had the same biological parents as all other children in the sibship, and who lived in the same household. Information on birth weight was collected from hospital records. Results showed that male newborns with older brothers weighed less than male newborns with older sisters. In contrast, the weight of female newborns with older brothers did not differ from the weight of female newborns with older sisters. One explanation of these results is that maternal immunoreactivity to some male-specific feature of the fetus affects prenatal development and consequently reduces birth weight in males. The relation between older brothers and birth weight may have theoretical significance for behavioural variables.

Type
Regular Articles
Copyright
© 2003 Cambridge University Press

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