I have taken up the habit of feeding my newborn every 4 hours during the day, since we left the maternity. However, sometimes when the time to feed her comes, she's sleeping.
Should I wait until she wakes up by herself, or should I wake her up ?
You should talk to your pediatrician because the answer can depend on your baby and how well she drinks on an ad-lib diet (she gets to decide when and how much to drink).
When our baby was in the hospital (due to complications related to being a preemie), they would wake him up every 3 hours initially to feed him and then later changed that to 4 hours. He was later switched to ad-lib feeding. However, they took into considerations his needs (he was underweight) and I'm not sure what is recommended in general.
probably Joe has posted almost perfect link that covers answer in most cases. yet, just want to emphasis on one thing. you also need to listen to your baby. To see if baby's growth chart is fine you will have to wait until next doctor's appointment when they do wight and height check up and let you know how his growth chart looks.
in most cases as hospital suggests, new born baby needs food at every 2 hours during first 4 weeks and after that you can skip wake up calls during night. Because their belly is too small and i guess it can store something 25-35ml of liquid only. But again if baby is growing fast s/he may need feeding more frequently. mom will easily be able to tell if baby is actually eating or sleeping/playing while holding it. If baby is not hungry even by trying you can not make him/her eat more.
we just stick to 2 hour schedule in beginning and we were very happy when doctor said his chart looks perfect, no need to change anything and do what you are doing.
At least for 1 week see if 2hour schedule works. you should wake baby up at max 3 hours. if baby is not hungry and not eating even after 3hour, then let him/her sleep again. s/he will wake up when feels hungry.
slowly you get better idea what baby wants and accordingly you can adjust the feeding schedule. 1 hour plus/minus in schedule is not to worry.
Also another reason behind feeding at regular interval is, that controls the mom's milk production cycle. milk production will happen only if there is demand. is demand is consistent then production will be also regularly. and that why hospital also suggest that if baby skip some feeding interval mom should do the Pumping so her body doesn't stop cycle of milk production.
hope this will relieve some of your concerns.