I always thought effects such as environmental chemical pollution (estrogen analogs), overreliance on nighttime lighting / artificial temperature regulation and

I always thought effects such as environmental chemical pollution (estrogen analogs), overreliance on nighttime lighting / artificial temperature regulation and dietary issues leading to obesity (both previous items reducing fertility), and increasing cost of raising children (leading to higher investment in fewer children) are some of the main factors leading to decreases in birth rate in developed nations.