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Preterm (Premature) Newborns


Arcangela Lattari Balest

, MD, University of Pittsburgh, School of Medicine

Reviewed/Revised Oct 2022
Topic Resources

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

  • A previous preterm birth, multiple births, poor nutrition during pregnancy, late prenatal care, infections, assisted reproductive techniques (such as in vitro fertilization), and high blood pressure can increase the risk of a preterm birth.

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

  • 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 of survivors have mild or no long-term problems.

  • Early prenatal care may decrease the risk of a preterm birth.

  • 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).

Gestational age refers to how far along the fetus is. The gestational age is 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

  • Moderately 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.

Causes of Preterm Birth

The causes of preterm birth are frequently unknown. However, there are many known risk factors for preterm birth. Adolescents and older women, women of lower socioeconomic status, and women who have less formal education are at increased risk of preterm birth.

Risk factors from a previous pregnancy:

Risk factors before or during pregnancy:

However, most women who deliver a preterm newborn have no known risk factors.

Early prenatal care may decrease the risk of preterm birth.

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.

Extremely preterm newborns tend to require a longer stay in the 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 9% of newborns need special care after birth due to prematurity, problems... read more ) in the hospital until their organs can function well on their own. Late preterm newborns, on the other hand, may have only a few organ systems, if any, 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 of certain causes of 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, 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. Kidney problems may lead to growth failure and a buildup of acid in the blood (called metabolic acidosis Acidosis Acidosis is caused by an overproduction of acid that builds up in the blood or an excessive loss of bicarbonate from the blood (metabolic acidosis) or by a buildup of carbon dioxide in the blood... read more ).

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.

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 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 glucose 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) 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.

Heart problems

A common issue among less mature 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 9% of newborns need special care after birth due to prematurity, problems... read more ).

Diagnosis of Preterm Newborns

  • Appearance of the newborn

  • Gestational age

Doctors usually know whether a baby is born prematurely based on the newborn's calculated gestational age and physical features observed after birth. They examine the newborn and do any needed blood, laboratory, hearing, eye, and imaging tests as part of the routine newborn evaluation Physical Examination of a Newborn A newborn is usually given a thorough physical examination by a health care professional within the first 24 hours of life. The examination begins with a series of measurements, including weight... read more Physical Examination of a Newborn and screening Newborn Screening Tests Screening tests are done to detect health conditions that are not yet causing symptoms. Many serious disorders that are not apparent at birth can be detected by various screening tests. Early... read more . These screenings may need to be repeated frequently as the newborn grows and before discharge from the hospital.

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 itself is rare if infants are born at less than 23 weeks of gestation. Infants born at 23 to 24 weeks may survive, but few survive without some degree of neurologic injury. 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 stopping smoking may be the best approach to reducing the risk of prematurity. However, many of the conditions that increase the risk of prematurity cannot be avoided. In all cases, women 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.

Assisted reproductive techniques Assisted Reproductive Technologies Assisted reproductive technologies involve working with sperm and eggs or embryos in a laboratory (in vitro) with the goal of producing a pregnancy. (See also Overview of Infertility.) If treatment... read more Assisted Reproductive Technologies often result in multiple pregnancies (twins, triplets, and more). These pregnancies have a significantly increased risk of preterm delivery and its complications. However, a technique called elective single embryo transfer, which is the implantation of a single embryo, reduces the risk of a multiple pregnancy and may be considered a good option for some women.

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 uses high-frequency (ultrasound) waves bounced off internal structures to produce a moving image. It uses no x-rays. Ultrasonography of the heart (echocardiography) is one 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 9% of newborns need special care after birth due to prematurity, problems... read more ) between the newborn and the mother or father 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 unexplained 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 to sleep because sleeping on the stomach also increases the risk of SUID (see also 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 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

  • Taking an adequate amount of milk without special assistance

  • Gaining weight steadily

  • Able to maintain a normal body temperature in a crib

  • No longer having pauses in breathing (apnea of prematurity)

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 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 can be found here. Some hospitals offer an inspection service, but casual advice provided by an uncertified hospital staff member should not be considered equivalent to inspection 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.

More Information

The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.

  • Safe to Sleep®: Information for parents and caregivers about safe sleep practices for infants

  • National Highway Traffic Safety Administration: Child car seat inspection station locator: Information about where to get an installed car seat inspected or where to get help with installation

Drugs Mentioned In This Article

Generic Name Select Brand Names
Adbeon, Alphatrex, Beta 1 Kit, Beta Derm , Betanate , Betatrex, Beta-Val, BSP 0820, Celestone, Del-Beta , Diprolene, Diprolene AF, Diprosone, Luxiq Foam, Maxivate, ReadySharp Betamethasone, Sernivo, Valisone
Alymsys, Avastin, MVASI, Zirabev
Afrezza, Exubera
Cafcit, NoDoz, Stay Awake, Vivarin
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