Fertility of mega-urban regions 2020. Only 8 cities, Jakarta (Indonesia), Manila (Philippines), Cairo (Egypt), Karachi (Pakistan), Lagos (Nigeria), Johannesburg (South Africa), Lahore (Pakistan), and Kinshasa (DR Congo), out of 41 on the list, had fertility rates above replacement rate. At the top of the list is "Pearl River Delta", which is Shenzhen (China) and the surrounding metropolitan area (Dongguan, Foshan, Huizhou, Jiangmen, Zhongshan), with 55.7 million people and a total fertility rate of 1.10 children per woman, Tokyo (Japan) with 38.4 million people and a fertility rate of 1.2, Shanghai (China) with 38.0 million people and a fertility rate of 0.95, and Dehli (India) with 30.3 million people and a fertility rate 1.6. The table also shows fertility rates for the country the metro area is in, and you can see it is lower for all 41 metro areas on the table. Which suggests that urbanization causes fertility declines. Though correlation is not causation, as the famous saying goes, so you still have to prove causation. From a Twitter account called "Birth Gauge (@BirthGauge)", a Twitter account apparently created solely for "tracking the global fertility decline".
