At what age?

Does anyone know at what age babies can start sleeping through the night? My baby girl will be a month old in a few days and at night I have to wake her up for her feedings or she will sleep right through them, but when I wake her up she is definitely hungry. At the hospital I was told I needed to wake her every 4 hours if she wasn't waking up on her own but I was never told that when I had my son 6 years ago.