This paper analyses the effect of fertility decline on the sex ratio at birth in various regions of the world including the states and provinces of India and China. Two important findings emerge. First, we find that there is no monotonic relationship between sex ratio and fertility decline; rather there is a distinct zig-zag pattern, worsening of the sex ratio when odd (5, 3 and 1) levels of fertility are approached and improvement when the move is towards even (4 and 2) fertility levels. This augurs well for the future of this important gender bias variable – the model forecasts that India will have little sex preference at birth when it reaches the expected fertility level of 2 in 2016. The second major conclusion pertains to the estimate of the proportion of couples practicing sex-selection at birth (the missing girl at birth). This is most often no more than 2 percent of all births, a number considerably smaller than commonly assumed.