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Preterm (Premature) Newborns

By

Arcangela Lattari Balest

, MD, University of Pittsburgh, School of Medicine

Reviewed/Revised Jan 2024
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A preterm newborn is a baby delivered before 37 weeks of gestation. Depending on when they are born, preterm newborns may have underdeveloped organs that are not be ready to function outside of the uterus.

  • A previous preterm birth, multiple gestation (such as twins), poor nutrition during pregnancy, lack of regular prenatal care, infections, use of assisted reproductive technologies (such as in vitro fertilization), and high blood pressure can increase the risk of a preterm birth.

  • If organs are underdeveloped, preterm newborns may have difficulty breathing and feeding and are prone to bleeding in the brain, infections, and other problems.

  • Preterm birth can sometimes be delayed for a brief period by giving the mother medications to slow or stop contractions.

  • When an infant is expected to be delivered significantly early, doctors can give the mother injections of a corticosteroid to speed the development of the fetus’s lungs and help prevent bleeding in the brain (intraventricular hemorrhage).

  • The earliest and smallest preterm newborns are at far greater risk of having problems, including developmental problems.

  • Although some preterm newborns grow up with permanent problems, the majority have mild or no long-term problems.

Gestational age refers the number of weeks of pregnancy. The gestational age is determined by counting the number of weeks between the first day of the mother's last menstrual period and the day of delivery. This time frame is often adjusted according to other information doctors receive, including the results of early ultrasound scans, which give additional information regarding the gestational age. The baby is estimated to be due (the due date) at 40 weeks of gestation.

Newborns are classified by gestational age as preterm if they are delivered before 37 weeks of gestation. Preterm infants are further categorized as

  • Extremely preterm: Delivered before 28 weeks of gestation

  • Very preterm: Delivered at 28 to before 32 weeks of gestation

  • Moderate preterm: Delivered at 32 to before 34 weeks of gestation

  • Late preterm: Delivered at 34 to before 37 weeks of gestation

About 1 of every 10 infants born in the United States is born before full term. Greater degrees of prematurity are associated with greater risks of serious and even life-threatening complications.

Risk Factors for Preterm Birth

The causes of preterm birth are frequently unknown. Although there are many known risk factors for preterm birth, there is no identifiable cause for most preterm deliveries.

Risk factors related to a previous pregnancy:

Risk factors related to the current pregnancy:

Risk factors related to maternal health or personal history:

Symptoms of Preterm Newborns

Preterm newborns usually weigh less than 5½ pounds (2.5 kilograms), and some weigh as little as 1 pound (½ kilogram). Symptoms often depend on immaturity of various organs.

Late preterm newborns may have only a few, if any, organ systems that need time to mature. Late preterm newborns may stay in the hospital until they can regulate their body temperature and the level of sugar (glucose) in their blood, eat well, and gain weight.

The immune system in any preterm newborn is also underdeveloped, and therefore preterm newborns are prone to infections.

Physical Features of a Preterm Newborn

Complications of Preterm Birth

Most complications of prematurity are caused by underdeveloped and immature organs and organ systems. The risk of complications increases with the degree of prematurity. Risk of complications also depends in part on the presence in the mother of certain risk factors for prematurity, such as infection, diabetes, high blood pressure, or preeclampsia.

Underdeveloped brain

Several problems arise when an infant is born before the brain is fully developed. These problems include

Underdeveloped digestive tract and liver

An underdeveloped digestive tract and liver can cause several problems, including the following:

Underdeveloped immune system

Infants born very prematurely have low levels of antibodies Antibodies One of the body's lines of defense ( immune system) involves white blood cells (leukocytes) that travel through the bloodstream and into tissues, searching for and attacking microorganisms and... read more Antibodies , which are proteins in the blood that help protect against infection. Antibodies from the mother cross the placenta late in the pregnancy and help protect the newborn from infection at birth.

Preterm newborns have fewer of their mother's protective antibodies and therefore are at higher risk of developing infections, especially infection in the blood (sepsis in the newborn Sepsis in Newborns Sepsis is a serious bodywide reaction to infection spread through the blood. Newborns with sepsis appear generally ill—they are listless, do not feed well, often have a gray color, and may have... read more ) or tissues around the brain (meningitis Bacterial Meningitis in Newborns Bacterial meningitis is inflammation of the layers of tissue surrounding the brain and spinal cord (meninges) caused by bacteria. Newborns with bacterial meningitis are usually irritable, vomit... read more ). The use of invasive devices for treatment after birth, such as catheters in blood vessels and breathing tubes (endotracheal tubes), further increases the risk of developing serious bacterial infections.

Underdeveloped kidneys

Before delivery, waste products produced in the fetus are removed by the placenta and then excreted by the mother’s kidneys. After delivery, the newborn’s kidneys must take over these functions. Kidney function is diminished in very preterm newborns but improves as the kidneys mature. Newborns with underdeveloped kidneys may have difficulty regulating the amount of salt and other electrolytes as well as water in the body.

Underdeveloped lungs

The lungs of preterm newborns may not have had enough time to fully develop before birth. The tiny air sacs called alveoli that absorb oxygen from the air and remove carbon dioxide from the blood are not formed until about the beginning of the last third of pregnancy (third trimester). In addition to this structural development, the tissues of the lungs must make a fatty material called surfactant. Surfactant coats the inside of the air sacs and allows them to remain open throughout the breathing cycle, making it easy to breathe. Without surfactant, the air sacs tend to collapse at the end of each breath, making breathing very difficult. Usually, the lungs do not make surfactant until about 32 weeks of pregnancy, and production is typically not adequate until about 34 to 36 weeks.

These factors mean that babies born early are at risk of breathing problems, including respiratory distress syndrome Respiratory Distress Syndrome in Newborns Respiratory distress syndrome is a lung disorder in premature newborns in which the air sacs in their lungs do not remain open because a substance that coats the air sacs called surfactant is... read more (RDS). Newborns with breathing problems may need help with breathing with a ventilator Mechanical Ventilation Mechanical ventilation is use of a machine to aid the movement of air into and out of the lungs. Some people with respiratory failure need a mechanical ventilator (a machine that helps air get... read more (a machine that helps air get in and out of the lungs). The more preterm the newborn, the less surfactant is available, and the greater the likelihood that respiratory distress syndrome will develop.

There is no treatment to make the lung structure mature more rapidly, but with adequate nutrition, the lungs continue to mature over time.

There are two approaches to increase the amount of surfactant and reduce the likelihood and severity of respiratory distress:

  • Before birth: Corticosteroid medications such as betamethasone increase surfactant production in the fetus and are given to the mother by injection when a preterm delivery is anticipated, typically 24 to 48 hours before delivery.

  • After birth: Doctors may give surfactant directly into the newborn's windpipe (trachea).

Bronchopulmonary dysplasia Bronchopulmonary Dysplasia (BPD) Bronchopulmonary dysplasia is a chronic lung disorder in newborns caused by extended use of a ventilator (a machine that helps air get in and out of the lungs), extended need for supplemental... read more (BPD) is a chronic lung disorder that can occur in preterm newborns, particularly the least mature infants. Most infants who have BPD have had respiratory distress syndrome and needed treatment with a ventilator. In BPD, the lungs develop scar tissue and the infant needs continued help with breathing, sometimes with a ventilator. In most cases, the infant very slowly recovers from the disease.

Infants who are born prematurely are at increased risk of becoming seriously ill if they are infected with respiratory syncytial virus Respiratory Syncytial Virus (RSV) Infection and Human Metapneumovirus Infection Respiratory syncytial virus infection and human metapneumovirus infection cause upper and sometimes lower respiratory tract infections. Respiratory syncytial virus is a very common cause of... read more (RSV). To prevent RSV, some infants are given a medication called nirsevimab or, if nirsevimab is not available, a medication called palivizumab. Additionally, pregnant people who are expected to give birth during RSV season can receive an RSV vaccine later in the third trimester. This vaccine given during pregnancy helps protect the newborn from RSV for about 6 months after birth because protective antibodies transfer from mother to fetus through the placenta (see also Prevention of RSV Prevention Respiratory syncytial virus infection and human metapneumovirus infection cause upper and sometimes lower respiratory tract infections. Respiratory syncytial virus is a very common cause of... read more ).

Underdeveloped eyes

The retina Structure and Function of the Eyes The structures and functions of the eyes are complex. Each eye constantly adjusts the amount of light it lets in, focuses on objects near and far, and produces continuous images that are instantly... read more is the light-sensitive tissue at the back of the eye. The retina is nourished by blood vessels on its surface. The blood vessels grow from the center of the retina to the edges during the course of the pregnancy and do not finish growing until near term.

In preterm infants, particularly the least mature infants, the blood vessels may stop growing and/or grow abnormally. Many preterm infants need extra oxygen, and this also can cause the blood vessels of the retina to grow abnormally. The abnormal vessels can bleed or cause scar tissue that can pull on the retina. This disorder is called retinopathy of prematurity Retinopathy of Prematurity (ROP) Retinopathy of prematurity is a disorder of premature infants in which the small blood vessels in the back of the eye (retina) grow abnormally. Retinopathy of prematurity is strongly associated... read more and it occurs after birth. In the most severe cases, the retina detaches from the back of the eye and causes blindness.

Preterm infants, particularly those born before 31 weeks of gestational age, typically have periodic eye examinations so doctors can look for abnormal development of the blood vessels. If there is a high risk of retinal detachment, doctors may use laser treatments or give a medication called bevacizumab.

Difficulty regulating blood sugar, mineral, and hormone levels

Because preterm newborns have difficulty feeding and maintaining normal blood sugar (glucose) levels, they are often treated with glucose solutions given by vein (intravenously) or given small, frequent feedings. Without regular feedings, preterm newborns may develop low blood sugar levels (hypoglycemia Hypoglycemia Hypoglycemia is abnormally low levels of sugar (glucose) in the blood. Hypoglycemia is most often caused by medications taken to control diabetes. Much less common causes of hypoglycemia include... read more ). Most newborns with hypoglycemia do not develop symptoms. Other newborns become listless with poor muscle tone, feed poorly, or become jittery. Rarely, seizures develop.

Preterm newborns are also prone to developing high blood sugar levels (hyperglycemia Diabetes Mellitus (DM) in Children and Adolescents Diabetes mellitus is a disorder in which blood sugar (glucose) levels are abnormally high because the body does not produce enough insulin or fails to respond normally to the insulin produced... read more Diabetes Mellitus (DM) in Children and Adolescents ) if they have an infection or bleeding in the brain or receive too much glucose intravenously. However, hyperglycemia rarely causes symptoms and can be controlled by limiting the amount of glucose given to the newborn or by using insulin for a short period of time.

Preterm newborns, particularly extremely preterm infants, may develop metabolic bone disease. Metabolic bone disease is a reduction in the minerals in bone. A preterm newborn may have inadequate mineral reserves because most calcium and phosphorus reserves are acquired between 25 and 40 weeks of gestation.

Some preterm newborns do not produce enough thyroid hormone (have hypothyroidism) because of their prematurity. Sometimes, it is difficult to differentiate the temporary hypothyroidism in a preterm newborn from permanent congenital hypothyroidism Hypothyroidism in the Newborn Hypothyroidism is decreased production of thyroid hormone. Hypothyroidism in the newborn may occur if there is a structural problem with the thyroid gland. Symptoms may include delayed growth... read more , which usually results from a defect in thyroid gland development. Preterm newborns sometimes need to be treated with thyroid hormone for some period of time. At first, newborns may have no symptoms. Later, if hypothyroidism remains undiagnosed or untreated, various symptoms develop. The newborn may become sluggish (lethargic) and have a poor appetite, yellowing of the skin (jaundice), low muscle tone, constipation, and a low heart rate. Eventually, if still untreated, the infant may develop dry, cool, mottled skin, coarse facial features (such as a flat, broad nasal bridge and a puffy face), coarse hair, abdominal swelling, low blood pressure, a low number of red blood cells (anemia), and an enlarged tongue.

Heart problems

A common issue among preterm infants is a patent ductus arteriosus Patent Ductus Arteriosus In patent ductus arteriosus (PDA), the blood vessel connecting the pulmonary artery and the aorta (ductus arteriosus) fails to close as it usually does shortly after birth. Patent ductus arteriosus... read more Patent Ductus Arteriosus (PDA). The ductus arteriosus is a blood vessel in the fetus that connects the two large arteries leaving the heart, the pulmonary artery and the aorta (see Normal Fetal Circulation Normal Fetal Circulation About one in 100 babies is born with a heart defect. Some are severe, but many are not. Defects may involve abnormal formation of the heart's walls or valves or of the blood vessels that enter... read more ). In a full-term infant, the muscle wall of the ductus arteriosis closes the blood vessel in the first few hours or days of life. In preterm infants, however, the blood vessel may stay open, resulting in excessive blood flow through the lungs and requiring more work from the heart.

In most preterm infants, the PDA eventually closes on its own, but medications are sometimes given to help the PDA close more quickly. In some cases, a surgical procedure to close the PDA is done.

Difficulty regulating body temperature

Body temperature is maintained by the brain. Because preterm newborns do not have a mature brain, they have trouble regulating their body temperature.

Preterm newborns have a large skin surface area relative to their weight compared to full-term newborns, so they tend to lose heat rapidly and have difficulty maintaining normal body temperature, especially if they are in a cool room, there is a draft, or they are near a window when it is cold outside. If the baby is not kept warm, the body temperature falls (called hypothermia Hypothermia Hypothermia (dangerously low body temperature) is often regarded as a cold injury, because it can be caused or made worse by exposure to cold surroundings. Being in an environment that is too... read more ). Newborns who have hypothermia gain weight poorly and may have a number of other complications. To prevent hypothermia, preterm babies are kept warm in an incubator or with an overhead radiant warmer (see Neonatal intensive care unit [NICU] Neonatal intensive care unit (NICU) Problems in newborns may develop Before birth while the fetus is growing During labor and delivery After birth About 10% of newborns need some special care after birth due to prematurity, problems... read more ).

Diagnosis of Preterm Newborns

  • Gestational age and appearance of the newborn

  • Screening tests

Doctors base a diagnosis of prematurity on the best estimate of the newborn's gestational age. The gestational age is calculated by counting the number of weeks between the first day of the mother's last normal menstrual period and the date of delivery. Sometimes gestational age is calculated by reviewing the first ultrasound of the fetus that was taken early in pregnancy. How the newborn looks after birth can also help doctors estimate gestational age.

Treatment of Preterm Newborns

  • Treatment of complications

Treatment of prematurity involves managing the complications resulting from underdeveloped organs. All specific disorders are treated as needed. For instance, preterm newborns may be given treatments that help with breathing problems (such as mechanical ventilation for lung disease and surfactant treatment), antibiotics for infections, blood transfusions for anemia, and laser surgery for eye disease or they may need special imaging studies like echocardiography Echocardiography and Other Ultrasound Procedures Ultrasonography is a type of medical imaging that uses high-frequency (ultrasound) waves to produce a moving image of internal organs and other tissues. Echocardiography is ultrasonography of... read more Echocardiography and Other Ultrasound Procedures for heart problems.

Parents are encouraged to visit and interact with their newborn as much as possible. Skin-to-skin contact (also called kangaroo care—see Neonatal intensive care unit (NICU) Neonatal intensive care unit (NICU) Problems in newborns may develop Before birth while the fetus is growing During labor and delivery After birth About 10% of newborns need some special care after birth due to prematurity, problems... read more ) between the newborn and parents is beneficial to the newborn whenever possible and facilitates bonding.

Parents of all infants should remove fluffy materials including blankets, quilts, pillows, and stuffed toys from the infant's crib at home because these items may increase the risk of sudden unexpected infant death Sudden Infant Death Syndrome (SIDS) Sudden infant death syndrome is the sudden, unexpected death, usually during sleep, of a seemingly healthy infant between 1 month and 1 year of age. The cause of sudden infant death syndrome... read more (SUID). Infants at home should be placed on their back and not their stomach for every sleep because sleeping on the stomach also increases the risk of sudden infant death syndrome (SIDS) (see also Prevention of SIDS Sudden Infant Death Syndrome (SIDS) Sudden infant death syndrome is the sudden, unexpected death, usually during sleep, of a seemingly healthy infant between 1 month and 1 year of age. The cause of sudden infant death syndrome... read more and the Safe to Sleep campaign).

Very preterm newborns

Very preterm newborns may need to be hospitalized in a neonatal intensive care unit for days, weeks, or months. They may require a breathing tube and a machine that helps air get in and out of the lungs (ventilator Mechanical Ventilation Mechanical ventilation is use of a machine to aid the movement of air into and out of the lungs. Some people with respiratory failure need a mechanical ventilator (a machine that helps air get... read more ) until they are able to breathe on their own.

They receive nutrition into their veins until they can tolerate feedings into their stomach through a feeding tube Tube Feeding Tube feeding may be used to feed people whose digestive tract is functioning normally but who cannot eat enough to meet their nutritional needs. Such people include those with the following... read more Tube Feeding and eventually feedings by mouth. The mother’s breast milk is the best food for preterm infants. Use of breast milk Breastfeeding Breast milk is the ideal food for newborns and infants. Although babies may be fed breast milk or formula, the World Health Organization (WHO) and American Academy of Pediatrics (AAP) recommend... read more Breastfeeding decreases the risk of developing an intestinal problem called necrotizing enterocolitis Necrotizing Enterocolitis (NEC) Necrotizing enterocolitis is injury to the inner surface of the intestine. This disorder occurs most often in newborns who are premature and/or seriously ill. The abdomen may be swollen, stools... read more and infections. Because breast milk is low in some nutrients like calcium, it may need to be mixed with a fortifying solution for newborns who have a very low birthweight. Infant formulas made specifically for preterm infants that are high in calories also can be used when necessary.

Very preterm newborns may require a medication that prompts them to breathe, such as caffeine, until the part of the brain that controls regular breathing has matured.

To keep warm, these newborns need to be kept in an incubator until they are able to maintain a normal body temperature.

Extremely preterm newborns

Extremely preterm newborns require all the same care as very preterm newborns. Like very preterm newborns, these newborns cannot be released from the hospital until they are able to breathe on their own, take oral feedings, maintain a normal body temperature, and gain weight.

Discharge from the hospital

Preterm infants typically remain hospitalized until their medical problems are under satisfactory control and they are

Most preterm infants are ready to go home when they are at 35 to 37 weeks of gestational age and weigh 4 to 5 pounds (2 to 2.5 kilograms). However, there is wide variation. The length of time the infant stays in the hospital does not affect the long-term prognosis.

Because preterm newborns are at risk of stopping breathing (apnea) and of having low levels of oxygen in the blood and a slow heart rate while in a car seat, many hospitals in the United States do a car seat challenge test before preterm babies are discharged. The test is done to determine whether babies are stable in the semi-reclined position of a car seat. This test is usually done using the car seat provided by the parents. Preterm babies, including those who pass the test, should be observed by a non-driving adult during all car seat travel until the babies have reached the due date and have remained consistently able to tolerate being in the car seat. Because the baby's color should be observed, travel should be limited to daylight hours. Long trips should be broken up into 45- to 60-minute segments so that the baby can be taken out of the car seat and repositioned.

Surveys show that most car seats are not installed optimally, so a check of the car seat by a certified car seat inspector is recommended. Inspection sites in the United States can be found through the National Highway Traffic Safety Administration. Some hospitals offer an inspection service. Car seat installation advice should be given only by a certified car seat expert.

The American Academy of Pediatrics recommends that car seats be used only for vehicular transportation and not as an infant seat or bed at home. Many doctors also recommend that parents do not put preterm infants in swings or bouncy seats for the first few months at home.

After discharge, preterm infants are carefully monitored for developmental problems and receive physical, occupational, and speech and language therapy as needed.

Prognosis for Preterm Newborns

  • Birthweight

  • Degree of prematurity

  • Whether the mother was given corticosteroids for 24 to 48 hours before a preterm delivery

  • Complications that arise after birth

The sex of the baby also affects the likelihood of a good outcome: girls have a better prognosis than boys who have the same degree of prematurity.

Survival is rare if infants are born at less than 23 weeks of gestation. Infants born at 23 to 24 weeks may survive, but most have some neurologic problems. Most infants born after 27 weeks of gestation survive without neurologic problems.

Prevention of Preterm Birth

Regular prenatal care Medical Care During Pregnancy Ideally, a couple who is thinking of having a baby should see a doctor or other health care practitioner to discuss whether pregnancy is advisable. Usually, pregnancy is very safe. However,... read more , combined with identification and treatment of any risk factors or complications of pregnancy Complications of Pregnancy , and not smoking or using alcohol or illicit drugs may be the best approaches to reducing the risk of prematurity. However, many of the conditions that increase the risk of prematurity cannot be avoided. In all cases, pregnant people who think they may be in preterm labor or have had rupture of the membranes should contact their obstetrician immediately to arrange for appropriate evaluation and treatment.

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