For a scientific critique of the prenatal urinary fluoride study read
https://openparachute.wordpress.com/2017/09/21/fluoride-pregnancy-and-the-iq-of-offspring/

and

https://openparachute.wordpress.com/2017/09/24/maternal-urinary-fluorideiq-study-an-update/

The study has several flaws and cannot explain any more than about 3% of the variation of IQ values. This usually means the considered factor has no role.