Of the 110 billion people to have ever been born, maybe 2 billion have been born into more comfortable circumstances than the median child born in the United States today.
It’s absolutely capable of changing demography.
It’s not capable of providing consistent timing of pregnancies.
This Planned Parenthood link says in theory 96% effective, in reality 78% effective. (Caveat: their definition of "effective" is not quite clear.)
https://www.plannedparenthood.org/learn/birth-control/withdr...