What is the sex ratio at birth?

The sex ratio at birth (male divided by total births: M/F is often quoted as approximating 0.515. Many factors have been shown to influence this ratio, and these include both acute events and chronic circumstances, both of which may be man-made or natural. This study was carried out in order to attempt to narrow down the range for M/F from a large and internationally recognised dataset of countries reporting live births to the World Health Organisation (WHO). Male and female live births were obtained from a WHO (Health for All - HFA) database for the five year period 1996-2000, for all countries reporting to WHO, and for which these values were reported. This study analysed 88,875,750 live births. M/F is estimated at 0.5147 (95% CI: 0.5146-0.5148), quite close to the widely quoted value of 0.515. M/F may be less due to female foeticide which cannot be accurately assessed, an unavoidable limitation. Other limitations for M/F estimates such as these are broad, cyclic secular variations, broad demographic population changes, chronic stress and an overall declining M/F in industrialised countries.

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Declaration of competing interest There are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome.