I have heard this tripe spouted by women “I left my brain in x maternity ward 21 years ago”
A colleague once warned me about baby brain telling me “just you wait”
When the time came and I had returned to work he tried to suggest that my missing something he had said was evidence of this. I informed him in no uncertain terms that I just had less time and energy to waste on his bull shit
Baby brain is a myth ... hormones, discomfort, lack of sleep all cause lesser cognitive ability ...women suffer longer because of the tolls of pregnancy but any new father will also stop being the sharpest pick in the box. Tell him to fuck off and come back on broken sleep.