In our 30s, fertility declines - after 35, exponentially so -- and specifically for women.

CNN: Reproduction without sex, a liberating future

But Kenya and Uganda also did well on child deaths, though their fertility declines have stalled recently.

ECONOMIST: African child mortality

Given that my own research focused on infertility and IVF, I knew a woman's fertility declines rapidly at age 35 and becomes negligible by age 40.

CNN: Women, consider freezing your eggs

If the high-fertility nations were to see dramatic declines in Total Fertility Rates (TFRs, the number of children per woman during her reproductive life-time) we would need to see drastic cuts in reproductive rates in at least 40% of all nations and that would have to start today.

FORBES: Pro-Planet Is Pro-Choice

Other countries achieved similar declines in fertility during the same period.

ECONOMIST: China's population