What is the sex ratio at birth?

INTRODUCTION

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).

METHODS

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.

RESULTS

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.

DISCUSSION

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.