Kinda how population curves work actually. Usually parents in developing countries tend to have a lot of children because many of them die shortly after being born. As the GDP per capita and quality of life improves while infant mortality reduces this cultural bias of having more children tends to stick for a while. Meanwhile the existing large population gives rise to an even larger growth in population even though people on average have fewer children.

The world population should stabilise and even reduce by 2300 afaik.