Fit fertility rates with a gamma density $$ f(x)= R \frac{1}{\Gamma(b)c^b}(x-d)^{b-1}\exp\left(\frac{x-d}{c}\right),\quad x>d $$ The parameters \(R\), \(b\), \(c\) and \(d\) are chosen to minimize the square of the absolute error in fertility rates.