A change in behavior may be one of the first signs of illness in a newborn. It's normal for a baby's activity, appetite, and cries to vary from day to day, even hour to hour. But a distinct change in any of these areas may signal illness.

Generally, if your baby is alert and active when awake, is feeding well, and can be comforted when crying, occasional differences in these areas are normal. Consult your baby's doctor if you are worried about your baby's behavior. Some changes may mean an illness is present.

Lethargic or listless babies appear to have little or no energy. They are drowsy or sluggish. They may also sleep longer than usual. They may be hard to wake for feedings and, even when awake, are not alert or attentive to sounds and visual cues. Sometimes this can develop slowly and a parent may not notice the gradual change. Lethargy may be a sign of infection or other condition, such as low sugar (blood glucose). Ask your baby's doctor if your baby becomes lethargic or has a change in activity level.

Some babies have trouble feeding due to a sucking problem. This may show up when a baby starts out at birth with a strong, vigorous suck and over time becomes less effective at feedings. Or it may show up when a baby starts out with a weak suck and does not eat effectively. This is especially common if they were born prematurely. Babies with a weak suck may not pull strongly or have a good latch while breastfeeding. You may not hear your baby swallowing or gulping during feedings. Your breasts may not feel full right before a feeding, or you may not notice your breasts getting softer (emptying) after a feeding. If you notice your baby is unable to empty the breast effectively or suck at the bottle effectively, or if feedings take longer than 30 minutes, ask your baby's doctor.

• After the first day or so, most newborns are ready to eat every 2 to 4 hours. They will show signs of hunger by sucking on fingers or a hand, crying, and making rooting motions. A sick baby may refuse feedings. A baby who sleeps continuously and shows little interest in feeding may be ill.
• Spitting up and dribbling milk with burps or after feedings is fairly common in newborns. This is because the sphincter muscle is weak and immature. The sphincter muscle is between the stomach and the tube from the mouth to the stomach (the esophagus). But forceful or projectile vomiting, or spitting up large amounts of milk after most feedings, can mean a problem. Formula-fed babies may vomit after overfeeding, or because of an intolerance to formula. In breastfed or formula-fed babies, a physical condition that prevents normal digestion may cause vomiting. Discolored or green-tinged vomit may mean the baby has a blocked intestine.
• Weight loss up to about 10% of birth weight is normal in the first 5 to 7 days after birth. But the baby should reach their birth weight in 10 to 14 days. Signs a baby is not gaining weight may include a thin, drawn face, loose skin, and fewer wet or soiled diapers. Newborns should have at least 3 wet diapers a day. By 1 week of age, a baby should have at least 5 wet diapers a day. Most doctors want to see a newborn in the office at the end of the first week to check their weight. Lack of weight gain or continued weight loss in a young baby may be a sign of illness or other conditions that need to be treated.

Feeding problems can be a sign of other conditions and may lead to serious illness if untreated. Talk with your baby's doctor if your baby has any trouble taking or digesting feedings.

All babies cry. This is their only way of communicating their needs to you. Babies also develop different types of cries for different needs, including:

• Hunger
• Sleepiness
• Loneliness
• Needing a diaper change
• Pain

At first, parents may not know how to interpret cries. But they usually can comfort their baby by meeting those needs. But a baby who is always fretful and fussy, or cries for long periods, may be ill. Also, a baby may be very irritable if they are hurting. Jitteriness or trembling may also be signs of illness. Colic is crying that starts around 2 weeks of age, occurs in spells, lasts for a total of 2 to 3 or more hours daily, several times a week, and is difficult to stop. There are many theories and plenty of expert opinions, but no one is really sure about the causes of colic.

Check your baby carefully to make sure there isn't a physical problem, such as clothing pinching the baby, or a diaper pin sticking the baby. There may be a thread or even a hair tightly wound on a finger or toe. Look at your baby's belly for signs of swelling. Check to make sure your baby isn't too warm or cool. Call your baby's doctor right away if your baby is crying for longer than usual or has other signs of illness.