Preterm (Premature) Newborns

ByArcangela 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.

(See also Overview of General Problems in Newborns.)

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.

Extreme prematurity is the single most common cause of death in newborns. Also, newborns born very prematurely are at increased risk of long-term problems, especially delayed development, cerebral palsy, and learning disorders. Nonetheless, most infants who are born prematurely grow up with no long-term difficulties.

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.

Extremely preterm newborns tend to require a longer stay in the neonatal intensive care unit (NICU) in the hospital until their organs can function well on their own.

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

  • Small size

  • Large head relative to rest of the body

  • Little fat under the skin

  • Thin, shiny, pink skin

  • Veins visible beneath the skin

  • Few creases on soles of feet

  • Scant hair

  • Soft ears, with little cartilage

  • Underdeveloped breast tissue

  • Boys: Small scrotum with few folds; testes may be undescended in very preterm newborns

  • Girls: Labia majora (large lips) not yet covering labia minora (small lips) of the genitals

  • Rapid breathing with brief pauses (periodic breathing), apnea spells (pauses lasting 20 seconds or longer), or both

  • Weak, poorly coordinated sucking and swallowing reflexes

  • Reduced physical activity and muscle tone (a preterm newborn tends not to draw up the arms and legs when at rest as does a full-term 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

  • Inconsistent breathing: The part of the brain that controls regular breathing may be so immature that preterm newborns breathe inconsistently, with short pauses in breathing or periods during which breathing stops completely for 20 seconds or longer (apnea of prematurity).

  • Difficulty coordinating feeding and breathing: The parts of the brain that control reflexes involving the mouth and throat are immature, so preterm newborns may not be able to suck and swallow normally, resulting in difficulty coordinating feeding with breathing.

  • Bleeding (hemorrhage) in the brain: Newborns born very prematurely are at increased risk of bleeding in the brain.

  • Delays in development of motor, intellectual, social, and emotional skills

Underdeveloped digestive tract and liver

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

  • Frequent episodes of spitting-up: Initially, preterm newborns may have difficulty with feedings. Not only do they have immature sucking and swallowing reflexes, but their small stomach empties slowly, which can lead to frequent episodes of spitting up (reflux).

  • Frequent episodes of not tolerating feedings: The intestines of preterm newborns move very slowly, and preterm newborns frequently have difficulty passing stools. Because of the slow movement of the intestinal tract, preterm infants do not easily digest the breast milk or formula they are given.

  • Intestinal damage: Very preterm newborns may develop a serious condition in which part of the intestine becomes severely damaged and may cause infection (called necrotizing enterocolitis).

  • Hyperbilirubinemia: Preterm newborns are prone to developing hyperbilirubinemia. In hyperbilirubinemia, the newborn's liver is slow in clearing bilirubin (the yellow bile pigment that results from the normal breakdown of red blood cells) from the blood. Thus, the yellow pigment accumulates, giving the skin and the whites of the eyes a yellow color (jaundice). Preterm newborns tend to become jaundiced in the first few days after birth. Usually, jaundice is mild and resolves as newborns take in larger amounts during feedings and have more frequent bowel movements (bilirubin is removed in the stool, giving it its initial yellow color). Rarely, very high levels of bilirubin accumulate and put newborns at risk of developing kernicterus. Kernicterus is a form of brain damage caused by deposits of bilirubin in the brain.

Underdeveloped immune system

Infants born very prematurely have low levels of 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) or tissues around the brain (meningitis). 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.

Kidney problems may lead to growth failure and a buildup of acid in the blood (called metabolic acidosis).

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 (RDS). Newborns with breathing problems may need help with breathing with a ventilator (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:

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

Bronchopulmonary dysplasia (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 virusnirsevimabPrevention of RSV).

Underdeveloped eyes

The retina 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 and it occurs after birth. In the most severe cases, the retina detaches from the back of the eye and causes blindness.

Preterm newborns are also at increased risk of developing other eye problems, such as nearsightedness (myopia), misalignment of the eyes (strabismus), or both.

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). 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

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, 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 (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). 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). 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]).

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.

Newborns are examined, and any needed blood, laboratory, hearing, eye, and imaging tests as part of the routine newborn evaluation and screening are done. These screening tests may need to be repeated frequently as the newborn grows and before discharge from the hospital.

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 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)) 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 (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 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) 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 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 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.

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 breast milk, formula, or both 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) or a slow heart rate that requires treatment

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

The survival and overall outcome of preterm newborns have improved dramatically, but problems such as delayed development, cerebral palsy, vision and hearing impairments, attention-deficit/hyperactivity disorder (ADHD), and learning disorders are still more common among preterm infants than full-term infants. The most important factors in determining outcome are

  • 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, combined with identification and treatment of any risk factors or 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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