A premature birth means a baby is born too early. The birth takes place before the 37th week of pregnancy. A typical pregnancy lasts about 40 weeks.

Premature babies often have serious health problems, especially when they're born very early. These problems often vary. But the earlier a baby is born, the higher the risk of health challenges.

A newborn can be:

• Late preterm, born between 34 and 36 completed weeks of pregnancy.
• Moderately preterm, born between 32 and 34 weeks of pregnancy.
• Very preterm, born between 28 and 32 weeks of pregnancy.
• Extremely preterm, born before 28 weeks of pregnancy.

Most premature births happen in the late preterm stage.

Your baby may have very mild symptoms of premature birth or more-serious health problems.

Some signs of being born too early include:

• Small size, with a head that's large compared with the body.
• Features that are sharper and less rounded than a full-term baby's features due to a lack of cells that store fat.
• Fine hair that covers much of the body.
• Low body temperature, mainly right after birth in the delivery room.
• Trouble breathing.
• Feeding problems.

The following tables show the median birth weight, length and head circumference of premature babies at different gestational ages for each sex.

Special care

If you give birth to a preterm baby, your baby will likely need to stay in a special nursery unit at the hospital. Some infants need to spend time in a unit that cares for them and closely tracks their health day and night. This is called a neonatal intensive care unit (NICU).

A step down from the NICU is an intermediate care nursery, which provides less intensive care. Special nursery units are staffed with health care providers and a team that's trained to help preterm babies.

Your baby may need extra help feeding and adapting right after delivery. Your health care team can help you understand what's needed and what your baby's care plan will be. Feel free to ask them questions.

Often, the exact cause of premature birth isn't clear. But certain things can raise the risk.

Some risk factors linked to past and present pregnancies include:

• Pregnancy with twins, triplets or other multiples.
• A span of less than six months between pregnancies. It's ideal to wait 18 to 24 months between pregnancies.
• Treatments to help you get pregnant, called assisted reproduction, including in vitro fertilization.
• More than one miscarriage or abortion.
• A previous premature birth.

Some health problems can raise the risk of premature birth, such as:

• Problems with the uterus, cervix or placenta.
• Some infections, mainly those of the amniotic fluid and lower genital tract.
• Ongoing health problems such as high blood pressure and diabetes.
• Injuries or trauma to the body.

Lifestyle choices also can raise the risk of a preterm pregnancy, such as:

• Smoking cigarettes, taking illicit drugs or drinking alcohol often or heavily while pregnant.
• Being underweight or overweight before pregnancy.
• Becoming pregnant before the age of 17 or after 35.
• Going through stressful life events, such as the death of a loved one or domestic violence.

For unknown reasons, Black and Native people in the United States are more likely to have premature births than are women of other races. But premature birth can happen to anyone. In fact, many preterm births have no known risk factors.

Not all premature babies have health complications. But being born too early can cause short-term and long-term medical problems. In general, the earlier a baby is born, the higher the risk of complications. Birth weight plays a key role too.

Some problems may be clear at birth. Others may not show up until later.

Short-term complications

In the first weeks, the complications of premature birth may include:

• Breathing problems. A premature baby may have trouble breathing due to being born with lungs that aren't fully developed. If the baby's lungs lack a substance that allows the lungs to expand, the baby may have trouble getting enough air. This is a treatable problem called respiratory distress syndrome.

  It's common for preterm babies to have pauses in their breathing called apnea. Most infants outgrow apnea by the time they go home from the hospital. Some premature babies get a less common lung disorder called bronchopulmonary dysplasia. They need oxygen for a few weeks or months, but they often outgrow this problem.

• Heart problems. Some common heart problems that premature babies have are patent ductus arteriosus (PDA) and low blood pressure. PDA is an opening between two important blood vessels, the aorta and the pulmonary artery. This heart defect often closes on its own. But without treatment it can lead to problems such as heart failure. That's when the heart can't pump blood as well as it should. Low blood pressure may need to be treated with fluids given through a vein, medicines and sometimes blood transfusions.
• Brain problems. The earlier a baby is born, the greater the risk of bleeding in the brain. This is called an intraventricular hemorrhage. Most hemorrhages are mild and resolve with little short-term impact. But some babies may have larger brain bleeding that causes permanent brain injury.

• Temperature control problems. Premature babies can lose body heat quickly. They don't have the stored body fat of a full-term infant. And they can't make enough heat to counter what's lost through the surface of their bodies. If body temperature drops too low, it can lead to a dangerous problem called hypothermia.

  Hypothermia in a premature baby can lead to breathing problems and low blood sugar levels. A preterm infant also may use up all of the energy gained from feedings just to stay warm. That's why smaller premature babies need extra heat from a warmer or an incubator at first.

• Digestive problems. Premature infants are more likely to have digestive systems that aren't fully developed. This can lead to problems such as necrotizing enterocolitis (NEC). With NEC, the cells lining the bowel wall are injured. This problem can happen in premature babies after they start feeding. Premature babies who receive only breast milk have a much lower risk of getting NEC.
• Blood problems. Premature babies are at risk of blood problems such as anemia and newborn jaundice. With anemia, the body doesn't have enough red blood cells. All newborns have a slow drop in red blood cell count during the first months of life. But that drop may be greater in premature babies. With newborn jaundice, the skin and eyes look yellow. It happens because the baby's blood contains too much of a yellow-colored substance from the liver or red blood cells. This substance is called bilirubin. Jaundice has many causes, but it is more common in preterm babies.
• Metabolism problems. Premature babies often have problems with metabolism. That's the process by which the body changes food and drink into energy. Some premature babies may have a very low level of blood sugar. This can happen because premature infants often have smaller amounts of stored blood sugar than do full-term babies. Premature babies also have more trouble turning their stored sugar into more-usable, active forms of blood sugar.
• Immune system problems. It's common for premature babies to have immune systems that aren't fully developed. This can lead to a higher risk of illnesses. An infection in a premature baby can quickly spread to the bloodstream and cause a life-threatening problem called sepsis.

Long-term complications

Over the long term, premature birth may lead to health problems such as:

• Cerebral palsy. This group of disorders can cause problems with movement, muscle tone or posture. It can be due to an infection or poor blood flow. It also can stem from an injury to a newborn's brain, either early during pregnancy or while the baby is still young.
• Trouble learning. Premature babies are more likely to lag behind full-term babies on different milestones. A school-age child who was born too early might be more likely to have learning disabilities.
• Vision problems. Premature infants may get an eye disease called retinopathy of prematurity. This happens when blood vessels swell and grow too much in the light-sensing tissue at the back of the eye, called the retina. Sometimes these overgrown vessels slowly scar the retina and pull it out of place. When the retina is pulled away from the back of the eye, it's called retinal detachment. Without treatment, this can harm vision and cause blindness.
• Hearing problems. Premature babies have a higher risk of losing some hearing. All babies should have their hearing checked before they go home from the hospital.
• Dental problems. Preterm babies may be more likely than full-term babies to have defects with the hard outer covering of the teeth, called enamel. Infants born very or extremely early also may be more likely to have teeth that take longer to develop.
• Behavior and mental health problems. Children who were born early may be more likely than kids born full term to have certain mental health troubles, as well as delays in development.
• Ongoing health issues. Premature babies are more likely to have long-term health issues than are full-term infants. Illnesses, asthma and feeding problems are more likely to develop or linger. Premature infants also are at higher risk of sudden infant death syndrome (SIDS). That's when an infant dies for unclear reasons, often while asleep.

The exact cause of preterm birth is often unknown. But some things can be done to help lower the risk of preterm birth, including:

• Taking progesterone supplements. Progesterone is a hormone that plays a role in pregnancy. A lab-made version of it may be able to lower the risk of preterm birth if you've had a premature baby before. It also may lower the risk of preterm birth if you have a short cervix. The cervix is the lower end of the uterus, which opens during labor so a baby can be born.

• Cervical cerclage. This is a surgery that's done during pregnancy. Your provider may suggest it if you have a short cervix and you've had a preterm birth before.

  During this procedure, the cervix is stitched closed with a strong suture. This may give the uterus extra support. The suture is removed when it's time to have the baby. Ask your provider if you need to stay away from vigorous activity during the rest of your pregnancy.

One thing that doesn't help prevent preterm birth is staying in bed. Bed rest can raise the risk of blood clots, weaker bones and less muscle strength. It might even make preterm birth more likely.

A premature baby in the NICU may need to have many tests. Some tests are ongoing. Other exams may be done only if the NICU staff thinks the baby might have a certain health problem.

Tests your premature baby may need include:

• Breathing and heart rate monitoring. The baby's breathing and heart rate are tracked constantly. Blood pressure readings are done often too.
• Fluid input and output measurement. The NICU team tracks how much fluid your baby takes in through feedings and through a vein. The team also watches how much fluid your baby loses through wet or soiled diapers.

• Blood tests. Blood samples are taken by pricking the heel or placing a needle in a vein. These tests let the NICU staff closely watch the levels of important substances in your baby's blood, such as calcium and blood sugar. A blood sample also may be checked to look for signs of problems such as anemia or illnesses.

  Your baby's health care provider may need the NICU staff to take many blood samples. If so, the staff may insert a thin tube into a vein in the stump of the baby's cut umbilical cord. This way, the staff won't have to stick your baby with a needle each time blood is needed.

• Echocardiography. This imaging test is an ultrasound of the heart. It checks for problems with the way the heart works. It uses sound waves to make moving images on a display screen.
• Ultrasound. This imaging test may be done to check the brain for bleeding or fluid buildup. Or it can be used to check the organs in the stomach area for problems with the digestive tract, liver or kidneys.
• Eye exam. An eye doctor called an ophthalmologist may check your baby's eyes and vision to look for problems with the retina.

More tests may be needed if your baby has other health problems.

The neonatal intensive care unit (NICU) or special care nursery closely tracks your premature baby's health.

Supportive care

This type of care for your baby may include:

• Being placed in an incubator. The incubator is an enclosed plastic bassinet that your baby will probably stay in. It's kept warm to help the baby stay at a regular body temperature. Later on, NICU staff may show you a way to hold your baby with direct skin-to-skin contact. This is known as "kangaroo care."
• Tracking of your baby's vital signs. Sensors may be taped to your baby's body to track blood pressure, heart rate, breathing and temperature. A machine called a ventilator or a device called CPAP may be used to help your baby breathe.
• Having a feeding tube. At first your baby may receive fluids and nutrients through a tube in a vein. Breast milk may be given later through a tube passed through your baby's nose and into the baby's stomach. When your baby is strong enough to suck, breastfeeding or bottle-feeding often can be done.
• Getting enough fluids. Your baby needs a certain amount of fluids each day. The exact amount depends on the baby's age and health. The NICU team will closely track fluid, sodium and potassium levels to make sure that your baby's fluid levels stay on target. If fluids are needed, they'll be given through a tube in a vein.
• Spending time under bilirubin lights. To treat infant jaundice, your baby may be placed under a set of special lights. These lights help your baby's system break down extra bilirubin. That's a yellow-colored substance that builds up in the body if the liver can't process it all. Your baby will wear a protective eye mask while under the lights to rest more easily.
• Receiving blood from a donor. Some preterm babies need blood transfusions. This can be due to certain health problems, or because many blood samples have been taken for tests.

Medications

Medicines may be given to your baby for different reasons. For instance, some medicines help the lungs and heart work better. Depending on your baby's health, the medicines they receive may include:

• Surfactant, which is used to treat respiratory distress syndrome.
• Fine-mist or medicines given in a vein to strengthen breathing and heart rate.
• Antibiotics for an illness caused by bacteria, or if there's a risk of such an illness.
• Diuretics, which make the baby pee more to manage excess fluid.
• A shot of medicine into the eye to stop the growth of new blood vessels, which could cause the eye disease retinopathy.
• Medicine that helps close the heart defect called patent ductus arteriosus.

Surgery

Sometimes surgery is needed to treat a premature baby's health problems. Talk with your baby's health care team to understand which complications may lead to surgery. Learn about the types of surgery that might be needed to treat these problems too.

Taking your baby home

The following signs mean your baby is ready to go home:

• Can breathe without support.
• Has a stable body temperature.
• Can breastfeed or bottle-feed.
• Is gaining weight over time.
• Is free of major health problems.

The hospital may let a baby go home before meeting one of these requirements. But the baby's medical team and family first need to set up and agree on a plan for home care and follow-up health care.

Your baby's health care team will help you learn how to care for your baby at home. Before your baby can leave the hospital, your baby's nurse or a hospital discharge planner may ask you questions about:

• Where you live and who you live with.
• Other children in the home.
• Adult relatives and friends who may help you care for your baby.
• Who the baby's primary health care provider will be.

The thought of bringing your baby home from the hospital might make you feel relieved, excited and nervous. You can do some things ahead of time to prepare for life at home:

• Understand how to care for your baby. Before you leave the hospital, take a course in infant CPR. This can save the lives of babies who stop breathing. Ask your baby's medical team any questions you might have, and take notes.

  Make sure you're comfortable caring for your baby. This is very important if you'll need to use health monitors or give your infant medicines, oxygen or other treatments. Ask what symptoms to call your baby's health care provider about, such as breathing or feeding problems.

• Discuss feedings. Ask the medical team about your baby's need for extra nutrition. The team might suggest that you use products such as breast milk fortifier supplements or preterm infant formula. Keep in mind that premature babies often eat less and may need to be fed more often than full-term babies. Find out how much and how often your baby should eat.
• Limit contact with other people. Premature babies are more likely to get serious illnesses than are other newborns. Try to keep your baby away from crowded places as much as you can. And make sure everyone who comes into contact with your baby washes their hands first. Ask people who are ill to put off their visit until they are well.

• Protect your baby from RSV. Premature babies have a higher risk of getting a serious illness called RSV infection. This disease is caused by a virus. It affects the lungs and other organs involved in breathing.

  There are a few options to protect premature babies from severe RSV infection. One is an RSV vaccine for pregnant people that helps protect babies from birth through 6 months of age. The other is an antibody product given to the infant. This product is called nirsevimab (Beyfortus). Rarely, when nirsevimab is not available or a child is not eligible for it, another antibody product called palivizumab may be given.

• Follow a suggested schedule for checkups. Discuss your baby's need for future health checkups with your baby's care provider and any specialists. At first, your baby may need to see a primary care provider every week or two. That way the baby's growth, health needs and care can be watched closely.

• Get your baby vaccinated. Vaccines help protect people from dangerous diseases. It's suggested that vaccines be given to premature babies who are in stable health based on their age. Your baby's care team may talk to you about a schedule for when your baby should receive each vaccine. Delays in this schedule are common. Work with your baby's care provider to make sure your baby gets every vaccine on the schedule.

  Also make sure that other family members in your home are up to date on their vaccines, including shots for the flu and COVID-19. Family members and adult caregivers also should check with their health care providers to find out if they're up to date on their pertussis vaccine for whooping cough. If you're pregnant, make sure you're up to date on this vaccine too.

• Note any delays in development. Over the coming months, your baby's care provider may watch for any signs that the baby is taking longer than usual to reach key milestones. Babies who are at risk of such delays or disabilities may need more tests. You may be referred to services and support systems that can help, called early intervention services. The rules that determine who gets to use these services vary based on where you live.

Caring for a premature baby can be very tiring. You may be anxious about your baby's health. You also might feel angry, guilty or overwhelmed.

Some of these tips may help during this hard time:

• Learn everything you can about your baby's health. Talk to your baby's health care providers. Ask for pamphlets, books and trusted websites to get more information about taking care of your preterm baby.
• Take care of yourself. Get as much rest as you can. Eat healthy foods too. You'll feel stronger and better able to care for your baby.
• Build up your milk supply. Use a breast pump until your baby is able to breastfeed. Ask the hospital staff for help. They can show you how to use a breast pump and find the supplies you'll need to store milk.
• Accept help from others. Let friends and family help you. They could care for your other children, prepare food, clean the home or run errands. This helps you save your energy for your baby.
• Keep a journal. Write down the details of your baby's progress, along with your own thoughts and feelings. You may want to include pictures of your baby. That way you can see how much your child changes from week to week.
• Find good listeners for support. Talk to your partner or spouse, friends, family, or your baby's caregivers. The NICU social worker often can be helpful. If you're interested, your baby's caregivers may be able to suggest a support group in your area or online. Many parents find it very helpful to talk to other parents who take care of a preterm infant.

Caring for a premature baby is a great challenge. Take it one day at a time. Despite the worries and setbacks, celebrate your preemie's strength and ability to adapt. Cherish the time you can spend getting to know your child.

As the parent of a premature baby in the neonatal intensive care unit (NICU), you'll talk with many care providers for your baby. Members of the NICU team caring for your infant may include:

• Neonatal nurse — A registered nurse who has special training in caring for premature and high-risk newborns.
• Neonatal nurse practitioner — An experienced neonatal nurse who has completed extra training to assist doctors called neonatologists in caring for newborns.
• Pediatrician — A doctor who treats children from birth through the end of childhood.
• Neonatologist — A pediatrician who is trained to treat health problems in newborns.
• Pediatric resident — A doctor who is being trained to treat children.
• Respiratory therapist — A provider who helps care for newborns with breathing-related problems.
• Pediatric surgeon — A surgeon who is trained to do surgery for newborns and children.

You also might meet with a pediatric social worker. This professional can help you find services that might be useful during and after your baby's hospital stay.

Ideally, you'll work together with your baby's care providers. Over time, they can show you how to hold, feed and care for your baby.

What you can do

It's OK to ask the NICU care team any questions you have about your baby's condition. Or you can write down your questions and get answers when you're ready.

For instance, you could ask:

• How is my baby's health? Has anything changed?
• How does this equipment help my baby?
• Why are you giving my baby medicine?
• What types of tests does my baby need?

You also can ask how to help care for your baby:

• When can I hold my baby? Will you show me how?
• When can I try to breastfeed or bottle-feed my baby?
• Who should I contact if I have questions about my baby's care?
• Can I bring in a blanket or family photos to personalize my baby's incubator?

You may have questions about taking your baby home too:

• When will my baby be able to come home?
• What do I need to know about caring for my baby once we're home?
• How often do we need to come back to the hospital for follow-up visits?

During your baby's time in the NICU, feel free to ask the staff how you can become more involved in your baby's care. It can give you confidence as a new parent. It also can make life easier once you bring your child home.