A premature baby is one who is born too early, before 37 weeks of pregnancy. Each year, about 1 in 10 babies in the United States is born prematurely. Premature babies may not be fully developed at birth. They may have more health problems and may need to stay in the hospital longer than babies born later. Thanks to advances in medical care, even babies born very prematurely are more likely to survive today than ever before.

Your baby’s health care provider may use these terms to describe your baby’s birth:

Late preterm: Your baby is born between 34 and 36 completed weeks of pregnancy.

Moderately preterm: Your baby is born between 32 and 34 weeks of pregnancy.

Very preterm: Your baby is born at less than 32 weeks of pregnancy.

Extremely preterm: Your baby is born at or before 25 weeks of pregnancy.

Some health problems related to premature birth can last a lifetime. Other problems, like intellectual or developmental disabilities, can show up as your baby grows and later in childhood. These are problems with how the brain works that can cause a person to have trouble or delays in physical development, learning, communicating, taking care of himself or getting along with others.

The earlier in pregnancy a baby is born, the more likely he is to have health problems. Babies born before 34 weeks of pregnancy are mostly likely to have health problems, but babies born between 34 and 37 weeks of pregnancy are also at increased risk of having health problems related to premature birth. Some premature babies need to spend time in a hospital’s newborn intensive care unit (also called NICU). This is the nursery in a hospital where sick newborns get medical care. Premature babies stay in the NICU until their organs develop enough to stay alive without medical support. Some babies need NICU care for weeks or months until they can breathe on their own, eat by mouth and maintain their body temperature and body weight.

Do premature babies need special medical care?

Talk to your baby’s health care providers about any health conditions your baby has. He may be healthy enough to go home soon after birth, or he may need to stay in the NICU for special care. Your baby can probably go home from the hospital when he:

Weighs at least 4 pounds

Can keep warm on his own, without the help of an incubator. An incubator is a clear plastic bed that helps keep your baby warm.

Can breastfeed or bottle-feed

Gains weight steadily

Can breathe on his own

Your baby may need special medical equipment, medicine or other treatment after he leaves the hospital. Your baby’s provider and the staff at the hospital can help you with these things and teach you how to take care of your baby at home. They may recommend that you bring your baby to a neonatologist for checkups after your baby leaves the hospital. A neonatologist is a doctor who specializes in caring for premature babies and children. Talk to your baby’s provider if you have any questions about your baby’s health or long-term effects of premature birth. Hospital staff also can help you find parent support groups and other resources in your area that may be able to help you care for your baby.

What kinds of health problems can premature babies have?

Health problems that may affect premature babies include:

Anemia. This is when a baby doesn’t have enough healthy red blood cells to carry oxygen to the rest of the body. Anemia can cause low levels of oxygen and glucose (sugar) in a baby’s blood and make it hard for a baby’s organs to work properly. Premature babies in the NICU may have anemia because they get regular blood tests to check their health. They often can’t make new blood cells quickly enough to replace the blood cells they lose during blood tests. This can lead to anemia.

Breathing problems. These include:

Apnea of prematurity (also called AOP). This is a pause in breathing for 15 to 20 seconds or more. It may happen together with a slow heart rate called bradycardia.

Bronchopulmonary dysplasia (also called BPD). This is a lung disease that can develop in premature babies as well as babies who have treatment with a breathing machine. Babies with BPD have a higher risk of lung infections than other babies and BPD sometimes leads to lung damage.

Respiratory distress syndrome (also called RDS). If a baby has RDS, her lungs can’t make enough of a substance called surfactant. Surfactant is a slippery substance that keeps small air sacs in a baby's lungs from collapsing. 

Infections or neonatal sepsis. Premature babies can get infections more easily than other babies because their immune systems aren’t fully developed. The immune system protects your body from infection. Infection in premature babies can lead to sepsis, when the body has an extreme response to infection. Sepsis can be life-threatening. 

Intraventricular hemorrhage (also called IVH). This is bleeding in the fluid-filled spaces (also called ventricles) in the brain. The more premature a baby is, the more likely he is to have IVH.

Newborn jaundice. This is when your baby’s skin and the white parts of his eye look yellow. It’s caused by the build-up of a substance called bilirubin in your baby’s blood. Jaundice happens when a baby’s liver isn't fully developed or isn't working well.

Necrotizing enterocolitis (also called NEC). This is a common, but very serious problem that can affect a newborn baby’s intestines. Intestines are long tubes that are part of your digestive system. Your baby’s digestive system helps his body break down food, take in nutrients and remove waste. NEC happens when the tissue of the intestine is injured (damaged) or begins to die.

Patent ductus arteriosus (also called PDA). This is a heart condition that happens when a blood vessel called the ductus arteriosus doesn’t close properly. The ductus arteriosus helps blood go around a baby’s lungs before birth. Once a baby’s born and her lungs fill with air, the ductus arteriosis isn’t needed anymore and usually closes on its own a few days after birth. If it doesn’t close properly, too much blood may flow into the lungs. This can cause heart and breathing problems.

Retinopathy of prematurity (also called ROP). This is an eye disease that happens when a baby’s retina’s don’t fully develop in the weeks after birth. The retina is the nerve tissue that lines the back of the eye. ROP usually affects both eyes. Most babies with ROP have a mild case and don’t need treatment. But babies with severe ROP can have vision problems or blindness.