How will we know if our newborn baby is ill? We're worried that we won't be able to tell.

Some things to watch out for:

• Temperament - If your baby seems like her usual sunny, happy self and is feeding well, she's probably not seriously ill. This doesn't mean that you shouldn't make an appointment to see your doctor if she has a fever or the sniffles. But a baby who has a runny nose and a big smile is probably not as sick as a baby who has a runny nose and is lethargic.

• Unusual crying - If your baby suddenly starts crying more than usual and you can't comfort her in the usual ways, or if her cry is weak or unusually high-pitched, she may be seriously ill. The opposite is also true -- if your baby seems unhappy and doesn't cry but is unusually inactive and difficult to wake from sleep, call your doctor.

• Appetite - How hungry your baby is varies from day to day. But if she is hungry she should feed vigorously. A baby who tires easily from sucking or loses interest in nursing or feeding is probably sick. Also, if you notice your baby regurgitating her food more than usual, with more effort, or if the milk spit up is greenish in color, she may be sick.

• Abnormal bowel movements - Young babies, especially breastfed babies, may have very soft or liquid bowel movements. However, if your baby has diarrhea (watery stools), her tummy may be upset. Monitor her bowel movements and see whether the diarrhea continues. Make sure she is drinking lots of fluids or breastfeeding as often as usual so she doesn't get dehydrated. Your baby should wet a minimum of six diapers a day.

If your baby is acting sleepy and begins to have small, hard, or dry bowel movements, or if her stool is streaked with blood or mucus, or has the consistency of jelly, call your doctor.

• Difficulty breathing - If your baby's breathing is labored or if she's having trouble breathing at all, get help immediately.

• Fever - Although the presence of fever in a baby is a signal that she is sick, the fever alone is usually not a reason to be worried. A baby can have a low-grade fever and be seriously ill, or a high fever and be only mildly ill. However, if a baby under three months of age has a fever higher than 100 degrees F or 37.7 degrees C, she should be examined. If an older baby has a fever but appears completely well otherwise, observe her for a day to see whether she develops other symptoms.

If you're still in doubt, make an appointment with your doctor anyway. It's important for you to get peace of mind, and doctors expect to see tiny babies quite often .They know that they can become ill quite quickly. They also know they get better quickly too!