Do you buy a breast pump before or after you've had the baby?

I would suggest to buy first as I bought it after I delivered thinking that baby could latch on me without a pump. My baby was admitted to the hospital again one day after discharging from hospital due to dehydration. I did not know I was not providing enough milk and baby was not latching long enough (fell asleep) so he went into dehydration and jaundice raised and had to go under phototherapy. Most doctors will recommend to latch on, but for my case.. I did not know my milk supply wasn’t enough and I blamed myself for making baby ill. Now As I bought the spectra S1 double pump, I was able to see the amount and top up with formula if not sufficient. I feel more safe and secure knowing he’s drinking enough.