A change in behavior may be one of the first signs of illness in a newborn. Although a baby's activity level, appetite, and cries normally vary from day to day, even hour to hour, 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 have concerns about your baby's behavior. Some behavior changes may indicate an illness is present, including the following.

Listlessness or lethargy

A lethargic or listless baby may appear to have little energy. They may seem unusually drowsy or sluggish and may sleep longer than normal. These babies can be difficult to wake for feedings and, even when awake, may not be alert or responsive to sounds and visual stimulation.

Sometimes lethargy develops gradually, making it difficult for parents to recognize the change right away. Lethargy can be a sign of an infection or another condition, such as low blood glucose (blood sugar). Contact your baby's doctor if your baby becomes lethargic or shows a significant change in activity level.

Watch for:

• Sleeping much longer than usual
• Difficulty waking for feedings
• Low energy or unusual sluggishness
• Reduced alertness when awake
• Limited response to sounds or visual stimulation

Poor feeding

Feeding problems may include difficulty sucking at the breast or bottle, lack of interest in feeding, excessive spitting up, or weight loss.

Watch for:

• Difficulty sucking or latching
• Decreased interest in feeding
• Feedings that take longer than 45 minutes
• Frequent vomiting or excessive spitting up
• Weight loss or poor weight gain

Feeding problems can be a sign of underlying medical conditions and, if left untreated, may lead to serious illness. Consult your baby's doctor if your baby has difficulty taking or digesting feedings.

Difficulty sucking

Problems with sucking may become apparent when a baby who initially had a strong, vigorous suck gradually becomes less effective during feedings. In other cases, a baby may have a weak suck from birth and struggle to feed effectively. This is especially common in babies born prematurely.

Babies with a weak suck may not latch well during breastfeeding or may not pull strongly enough to feed effectively. Parents may not hear swallowing during feedings. A breastfeeding parent's breasts may not feel full before feedings or noticeably softer afterward. Bottle-fed babies with a weak suck may need additional stimulation of the nipple to encourage sucking. Feedings for both breastfed and bottle-fed babies with a weak suck may take an unusually long time, often longer than 45 minutes.

Signs of a weak suck may include:

• Poor latch during breastfeeding
• Weak or ineffective sucking
• Little or no swallowing heard during feedings
• Need for extra stimulation to continue sucking
• Unusually long feeding sessions

Lack of interest in feeding

After the first day or so, most newborns are ready to feed every 3 to 4 hours and show signs of hunger by sucking on their fingers or hands, crying, and rooting. A baby who is ill may show little interest in feeding or refuse feedings altogether. A newborn who sleeps continuously and does not wake to feed may also be ill.

Signs to watch for:

• Refusing feedings
• Sleeping through expected feeding times
• Little interest in feeding cues
• Not waking to eat

Vomiting and excessive spitting up

Spitting up small amounts of milk during burping or after feedings is common in newborns. This occurs because the sphincter muscle between the stomach and the esophagus (the tube connecting the mouth and stomach) is still immature.

However, forceful or projectile vomiting, or spitting up large amounts of milk after most feedings, may indicate a problem. In formula-fed babies, vomiting may occur because of overfeeding or a formula intolerance. In both breastfed and formula-fed babies, vomiting can sometimes be caused by a physical condition that interferes with normal digestion.

Contact your baby's doctor if you notice:

• Forceful or projectile vomiting
• Large amounts of milk spit up after most feedings
• Persistent vomiting
• Green-tinged or discolored vomit, which may be a sign of an intestinal obstruction

Weight loss

It is normal for newborns to lose up to about 10% of their birth weight during the first 2 to 3 days after birth. However, most babies should return to their birth weight by 10 to 11 days of age.

Most doctors recommend a weight check at the end of the first week of life. A lack of weight gain or continued weight loss in a young baby may be a sign of illness or another condition that requires treatment.

Possible signs of poor weight gain include:

• Thin or drawn facial appearance
• Loose skin
• Fewer wet diapers
• Fewer soiled diapers
• Continued weight loss after the first few days of life

Persistent crying or irritability

All babies cry—it is their primary way of communicating their needs. Babies may develop different cries to express hunger, tiredness, loneliness, discomfort from a wet diaper, or pain. At first, parents may find it difficult to interpret these cries, but over time they usually learn how to comfort their baby by meeting those needs.

If your child is unusually fussy, first check carefully for things that may be causing discomfort, such as tight or pinching clothing, diaper irritation, a hair or thread wrapped around a finger or toe, or a swollen belly that could indicate trapped gas.

A baby who is persistently fussy, difficult to console, or crying for unusually long periods may be ill. Babies may also become very irritable when they are in pain. Colic, a common intestinal condition, can cause prolonged, inconsolable crying.

Watch for:

• Crying longer than usual
• Difficulty consoling your baby
• Constant fussiness or irritability
• Jitteriness or trembling
• Other signs of illness along with crying

If you can't identify any source of the discomfort and your baby is crying longer than usual or has other signs of illness, contact your child's doctor promptly.