What are the signs and symptoms of the condition?

The baby's weight at birth can help predict how well the baby will do. Babies whose birth weight is less than 2,500 grams, or about 5.5 pounds, are called low-birth-weight, or LBW, infants. LBW babies make up only 7% of births. However, they account for two-thirds of newborn deaths. Babies whose birth weight is less than 1,500 grams, or about 3.25 pounds, are called very-low-birth-weight, or VLBW, infants. These babies make up about 1% of births. They account for half of newborn deaths.

There are many problems associated with being born early. One of the problems is respiratory distress syndrome. This occurs when the baby's lungs are too underdeveloped to work properly. A baby with immature lungs may have trouble breathing and need a ventilator. Some babies cannot get enough oxygen, even with a ventilator. The ventilator can sometimes cause damage to the lungs. If high levels of oxygen have to be used, the baby can develop eye problems. Premature babies can have lifelong difficulties with breathing.

Another problem is that these babies have underdeveloped immune systems. That means they are not very good at fighting infection. They can develop severe and deadly infections, such as group B streptococcal septicemia, more easily than a normal newborn. Extremely premature babies usually need to be given antibiotics often and for long periods of time. Some of the antibiotics can cause long-term problems.

When babies are born very early, they can have bleeding in their brains. This can cause mild to severe brain damage. Many extremely premature babies do not develop normally as they grow up. It is hard to predict which babies will have development problems.

Premature babies can also have problems in the gut, the kidneys, or the liver. They can have trouble controlling the level of sugars and salts in their bloodstream. They often develop anemia and sometimes need blood transfusions to treat it.