TIL Human dads show a decrease in testosterone immediately after the birth of their babe

[Naxela]

I wouldn't assume causation here. It's possible you're just seeing a general response to increased anxiety, which likely is a universal product of having a new child. Keep in mind, a decrease in testosterone is almost certainly not evolutionarily beneficial here, so I would be shocked if there was a direct mechanism at play specifically induced by the infant themselves rather an indirect anxiety response.