In the 18th and 19th centuries, Paris and other French cities experienced low fertility while the opposite was the case for Montreal, London, New York, Berlin and Amsterdam.

In cities today with diverse ethnicities, fertility rates often diverge. Mostly Jewish Jerusalem has a 40% Arab population. Since 2000, the fertility rate of its Jews increased from 3.8 to 4.3 while that of its Arabs decreased from 4.5 to 2.8.

London’s white British majority population saw its fertility rate decrease since 2000 from 1.6 to 1.3. London’s large Pakistani population, meanwhile, increased slightly to 2.45. Paris tells a similar story: the native population’s fertility rate fell while the immigrant rate remained stable.

In New York, the majority white non-Hispanic population rate rose from 1.2 to 1.6 while its black population plummeted from 2.3 to 1.5.

Same city, different populations, different result. Urbanization per se tells us little about effects on fertility rates.