"But changing gender in humans..."

Thank you for sharing an "alternative fact".  Now consider educating yourself:

https://www.washingtonpost.com/news/morning-mix/wp/2017/08/02/transgender-man-gives-birth-to-baby-boy-love-is-possible-he-says-so-is-being-a-loving-family/?utm_term=.3e56e392df55

He was even taking testosterone supplementation at the time he became pregnant.  This is a complex issue that doesn't lend itself to superficial assumptions.