After reading the many reviews and info on these bottles and giving birth to a colicky baby, I purchased TWO packs of these bottles (all different style/size nipples & bottle types). When she was a newborn they seemed way to fast.....I put them away for a month and they got them out again.....these things LEAK like there is no tomorrow! My baby is soaked after she tries to eat with one of these and they get the diaper bag, fridge--pretty much anywhere you put them--soaked in milk! I called the company and they said don't overfill (I don't), don't heat w/ parts in bottle (we don't), and don't shake with liquid (don't do that either--geez these bottles have a lot of rules!)and THEY STILL LEAK. The Gerbers that we got free at the hospital with their disposable nipples work much better. I wouldn't recommend these.