After baby is when you should start. I've heard pumping before baby can put you into labor? But I don't know if there is any truth to that
Your milk doesn't come in until after you have the baby anyway. And doing it early can cause uterus contractions that can lead to labor. You don't want to over stimulate your uterus either. So just wait.
Don't pump until after u have your baby. It causes contractions and my sent u to labor. Way more painful one. Since over stimulating ur nipples causes you to have alot of more pain. Besides your baby needs the colostrum as his first feeding and you don't produce milk til a 24 hours to 48 hours after delivery.