In John 16, Jesus compared the disciples' sorrow turning to joy with whom?

Answer: A woman giving birth

A woman in labor has pain, but forgets her anguish for joy once her child is born; so their grief would turn to joy.

“A woman has pain in childbirth because her time has come; but when she brings forth her child, she forgets her anguish because of her joy that a child has been born into the world.”— John 16:21 (BSB)