Low birth weight is a term used to describe babies who are born weighing less than 5 pounds, 8 ounces (2,500 grams). An average newborn usually weighs about 8 pounds. A low-birth-weight baby may be healthy even though they are small. But a low-birth-weight baby can also have many serious health problems.

Because most babies in the NICU are too small or sick to take milk feedings, medicines and fluids are often given through their veins or arteries.

Hypocalcemia is when a person doesn't have enough calcium in the blood. In babies, it’s called neonatal hypocalcemia. Your baby can get it at different times and from different causes.

Hyperbilirubinemia happens when there is too much bilirubin in your baby’s blood. Bilirubin is made by the breakdown of red blood cells. It’s hard for babies to get rid of bilirubin. It can build up in their blood, tissues, and fluids.

Hydrops fetalis is severe swelling (edema) in an unborn baby or a newborn baby. It is a life-threatening problem.

Vitamin K deficiency bleeding is a problem that occurs in some newborns. It happens during the first few days of life. This condition used to be called hemorrhagic disease of the newborn.

Respiratory distress syndrome (RDS) is a common problem in premature babies. It causes babies to need extra oxygen and help with breathing.

Very low birth weight is a term used to describe babies who are born weighing less than 3 pounds, 4 ounces. It is very rare that babies are born this tiny. Only about 1 in 100 babies born in the U.S. are very low birth weight.

Spina bifida is a birth defect that causes problems with the spine, spinal cord, and the surrounding nerves.

Craniosynostosis is a condition where one or more of the bones of the skull close too early. This can cause problems with normal brain and skull growth.