You will notice that many developing countries show a birth rate peak at around 1980. This is an artifact of the use of "net" birth rates.

Using net birthrates means that as the infant mortality rate drops ...as it did in most developing countries during the period 1950-1980, then the net birth rate rises and peaks around 1980 at which stage the real reduction in birth rate starts to be the dominant factor.

I need to fix this by the adoption of actual infant mortality rates.

It does not however affect long term population predictions.