Couples being apart and malnutrition are explanations that can only account for a small portion of the drop in fertility rates. The explanation is quite simple, during difficult times, people have a hard time finding jobs, so marriages are postponed, and even couples who do cohabitate go to great extents to avoid pregnancies.

OTOH, when the economy is healthy and/or there’s great deal of optimism about the future, people marry sooner and have plenty of kids.