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

Buy it in advance and also the right flange size as the standard ones given might not be suitable. You can do so by measuring your nipple + 4mm. It’s important to get the right flange size from day 1 so that you can start pumping effectively and get the flow going. I had to wait 4 days for the right flange to arrive and the first 4 days yielded very little milk for me. Once I got the size right it was a breeze to pump.