Answer:
the change in workers availability.
Step-by-step explanation:
Since the Urban areas typically have larger amount of job opportunities , high fertility rate can be accommodated in Urban Areas.
The opposite happened in Rural Area. Since this regions tend to be lacking in job opportunities, having high fertility rates typically increase the rate of unemployment in the future.
One thing that people do to deal with this problem is through commute. They have their family in rural areas and travel for longer hours everyday to work in Urban areas.