This seems counterintuitive, but turns out that as infant mortality is reduced, population sizes also decrease, because parents don't need to anticipate that their babies are going to die.
Se kuulostaa järjenvastaiselta, mutta itse asiassa lapsikuolleisuuden laskiessa väestönkootkin pienenevät, koska vanhempien ei tarvitse ennakoida lastensa kuolevan.