Avent nipples get clogged

[jubuguls]

Our Avent nipples constantly get clogged while feeding. They start off fine and during the feeding session, the nipples get clogged and my baby is just sucking without getting any food. We constantly have to check the drip on the nipples, run cold water through the nipples or change nipples during the middle of the feeding. When we run cold water through, it clears up the nipples temporarily.

We are using size 1 nipples(for newborns - she is 20 days old). We sterilize the bottles after each feeding and check the flow before each feeding. We feed her either formula (concentrate & powder) and/or breast milk but they all seem to clog the nipples at different times.

Any ideas? User error? Or should I just buy some different bottles/ nipples?

Thanks!