context: Wouldn't it be great if your newborn came home from the hospital with a set of instructions and rules that spelled out exactly when you need to call the pediatrician? But she doesn't. And your little one can't tell you what's wrong. So it's important to know the signs of serious problems. Trouble breathing. If your baby is breathing more than 60 breaths a minute, having pauses in breathing, or has a bluish tint to her skin, lips, and nails, it could be a lung or heart condition. Fever. If the baby's temperature measured in the rectum is 100.4 F or higher, she has a fever. For the first 3 months of your baby's life, take temperatures in the rectum, not in the ear, mouth, or under the armpit. Fever in newborns may be due to a serious condition such as bacterial meningitis or sepsis, a bloodstream infection. Both can be life-threatening if they aren't treated right away. Before you call, write down your child's temperature and the exact time you took it. Blood in vomit or stool. It may just be due to diaper rash, but it could also be a sign of a more serious stomach condition. Yellowish skin or eyes. This can be a sign of jaundice, which usually develops between the second and fourth day after birth. You can check by pressing gently on your infant's forehead -- if the skin looks yellow, she may have mild jaundice. Most hospitals check your newborn for jaundice before she goes home, but it can develop in breastfed babies anytime during the first week of life. Your pediatrician will check for it during the first office visit, 1-3 days after the baby leaves the hospital. Your baby is sleeping more than usual or won't wake up. It's true that most newborns can sleep pretty much through anything. But if your baby won't stir even after you've undressed her or prodded her a bit, it's time to call the doctor. Not eating. If your newborn refuses several feedings in a row or seems to be eating less than usual, check with your doctor. Not peeing. A healthy newborn has 6 to 8 wet diapers in 24 hours after day 4 of life. If she has fewer than that, she may be dehydrated. Other signs include sunken eyes and a sunken fontanel (the soft spot on your baby's head), and no tears when crying. Diarrhea. This can be hard to notice in a newborn, especially a breastfeeding one, as she has frequent, soft stools. If you suddenly notice more frequent bowel movements (for example, several while eating) or very watery ones, it could be diarrhea. Call your pediatrician if it goes on for 6-8 diaper changes. Constipation. Your newborn should have a bowel movement at least once a day during the first month. If she doesn't, call your doctor, as the baby may not be eating enough. After that, a formula-fed infant should have one at least one a day, but breastfed infants can go several days or even a week without one. If your baby is 1 month or older and is constipated (no pooping, or hard stool), you can try giving apple or pear juice (1 ounce a day for every month of life, so a 2-month-old would get 2 ounces). If that doesn't help after a day or two, call your pediatrician. A cold that doesn't get better. Even newborns come down with colds. Most of the time, the congestion and runny nose is uncomfortable for your little one but isn't serious. But call the doctor if your baby is so stuffed up she has trouble feeding or sleeping, if she seems especially cranky, or if nasal symptoms last longer than 10-14 days. Vomiting. It's normal for your newborn to spit up small amounts of milk within an hour after being fed. But if the flow is particularly forceful and happens more than two or three times in a day, call your doctor. It could indicate an infection, gastroesophageal reflux disease, or, in rare cases, pyloric stenosis, a thickening of stomach muscles that requires surgery. Tender belly button or penis. If your baby's umbilical area or penis (for circumcised boys) becomes red or starts to ooze or bleed, it could be a sign of a bacterial infection, and it needs antibiotic treatment right away. Diaper rash that doesn't go away. More than half of all babies get redness around their diaper area. You can treat it with a thick layer of zinc oxide or petroleum, but if it doesn't get better within 48 to 72 hours, bleeds, or you see pus-filled sores, call your doctor. Your baby may have a yeast or bacterial infection and will need medication. If you're worried, pick up the phone. It's always best to err on the side of caution, especially when it comes to newborns. Pediatricians' offices are used to fielding calls from anxious parents and can always help ease your worries or tell you what to do. Before calling your doctor, make sure to have a pen and paper to write down any instructions he might give. You should also have the following information on hand: Her temperature Any medical problems your baby has The names and doses of any medicine your newborn takes Your baby's immunization records