Merck Manual

Please confirm that you are a health care professional

honeypot link

Preterm Infants

By

Arcangela Lattari Balest

, MD, University of Pittsburgh, School of Medicine

Reviewed/Revised Nov 2023
View PATIENT EDUCATION
Topic Resources

An infant born before 37 weeks of gestation is considered preterm.

In 2021 in the United States, 10.48% of births were preterm (1 General references An infant born before 37 weeks of gestation is considered preterm. In 2021 in the United States, 10.48% of births were preterm ( 1), and in 2018, 26.53% of births were early term (significantly... read more ), and in 2018, 26.53% of births were early term (significantly increased from 26% in 2017) (2 General references An infant born before 37 weeks of gestation is considered preterm. In 2021 in the United States, 10.48% of births were preterm ( 1), and in 2018, 26.53% of births were early term (significantly... read more ). Preterm infants, even late preterm infants who are the size of some full-term infants, have increased morbidity and mortality compared to full-term infants because of their prematurity.

Gestational age

Gestational age Gestational Age Gestational age and growth parameters help identify the risk of neonatal pathology. Gestational age is the primary determinant of organ maturity. Neonatal gestational age is usually defined... read more is defined as the number of weeks between the first day of the mother's last normal menstrual period and the day of delivery. More accurately, the gestational age is the difference between 14 days before the date of conception and the date of delivery. Gestational age is not the actual embryologic age of the fetus, but it is the universal standard among obstetricians and neonatologists for discussing fetal maturation.

Birthweight

Preterm infants tend to be smaller than term infants. The Fenton growth charts provide a more precise assessment of growth vs gestational age (see figures and ).

Preterm infants are categorized by birthweight:

  • < 1000 g: Extremely low birthweight (ELBW)

  • 1000 to 1499 g: Very low birthweight (VLBW)

  • 1500 to 2500 g: Low birthweight (LBW)

General references

  • 1. Hamilton BE, Martin JA, Osterman MJ: Births: Provisional Data for 2021. National Center for Health Statistics. National Vital Statistics System, Vital Statistics Rapid Release Program, no 20. Hyattsville, MD. National Center for Health Statistics. 2022.

  • 2. Martin JA, Hamilton BE, Osterman MJ: Births in the United States, 2018. NCHS Data Brief, no 346. Hyattsville, MD. National Center for Health Statistics. 2019.

  • 3. Howson CP, Kinney MV, Lawn JE, editor: Born Too Soon: The Global Action Report on Preterm Birth. New York, March of Dimes, PMNCH, Save the Children, World Health Organization, 2012.

Etiology of Prematurity

Preterm delivery may be

  • Indicated because of obstetric risks or complications

  • Spontaneous because of preterm labor

Obstetric risks or complications

The American College of Obstetricians and Gynecologists (ACOG) recommends late preterm delivery in conditions such as multiple gestation with complications Complications Multifetal pregnancy is presence of > 1 fetus in the uterus. Multifetal (multiple) pregnancy occurs in up to 1 of 30 deliveries. Risk factors for multiple pregnancy include Ovarian stimulation... read more , preeclampsia Preeclampsia and Eclampsia Preeclampsia is new-onset or worsening of existing hypertension with proteinuria after 20 weeks gestation. Eclampsia is unexplained generalized seizures in patients with preeclampsia. Diagnosis... read more , placenta previa Placenta Previa Placenta previa is implantation of the placenta over or near the internal os of the cervix. It typically manifests as painless vaginal bleeding after 20 weeks gestation; the source of bleeding... read more / placenta accreta Placenta Accreta Placenta accreta is an abnormally adherent placenta, resulting in delayed delivery of the placenta. Placental function is normal, but trophoblastic invasion extends beyond the normal boundary... read more , and prelabor rupture of membranes Prelabor Rupture of Membranes (PROM) Prelabor rupture of membranes is leakage of amniotic fluid before onset of labor. Diagnosis is clinical. Delivery is recommended when gestational age is ≥ 34 weeks and is generally indicated... read more (1 Etiology references An infant born before 37 weeks of gestation is considered preterm. In 2021 in the United States, 10.48% of births were preterm ( 1), and in 2018, 26.53% of births were early term (significantly... read more ).

ACOG recommends delivery as early as 32 weeks in selected cases involving multiple gestation with complications. Quasi-elective delivery earlier than 32 weeks is done on a case-by-case basis to manage severe maternal and/or fetal complications.

Spontaneous preterm delivery

Past obstetric or gynecologic history:

Obstetric risk factors related to the current pregnancy:

Multiple gestation is an important risk factor; 59% of twins and > 98% of higher-order multiples are delivered prematurely. Many of these infants are very preterm; 10.7% of twins, 37% of triplets, and > 80% of higher-order multiples are delivered at < 32 weeks of gestation (4 General references An infant born before 37 weeks of gestation is considered preterm. In 2021 in the United States, 10.48% of births were preterm ( 1), and in 2018, 26.53% of births were early term (significantly... read more ).

Lifestyle or demographic risk factors:

It is unclear how much risk some of these lifestyle or demographic risk factors contribute independent of their effect on other risk factors (eg, nutrition, access to medical care).

Etiology references

Complications of Prematurity

The incidence and severity of complications of prematurity increase with decreasing gestational age and birthweight. Some complications (eg, necrotizing enterocolitis, retinopathy of prematurity, bronchopulmonary dysplasia, intraventricular hemorrhage) are uncommon in late preterm infants.

Most complications relate to dysfunction of immature organ systems. In some cases, complications resolve completely; in others, there is residual organ dysfunction.

Central nervous system (CNS)

CNS complications include

Infants born before 34 weeks of gestation have inadequate coordination of sucking and swallowing reflexes and need to be fed intravenously or by gavage. When to begin oral feedings is based on the infant's display of readiness cues for feeding, physiologic stability, and lack of need for advanced respiratory support (eg, ventilator, high-flow nasal catheters, CPAP). Evaluation for signs of feeding readiness does not begin until after 32 weeks postmenstrual age.

The periventricular germinal matrix (a highly cellular mass of embryonic cells that lies over the caudate nucleus on the lateral wall of the lateral ventricles of a fetus) is prone to hemorrhage, which may extend into the cerebral ventricles (intraventricular hemorrhage Intraventricular hemorrhage and/or intraparenchymal hemorrhage The forces of labor and delivery occasionally cause physical injury to the infant. The incidence of neonatal injury resulting from difficult or traumatic deliveries is decreasing due to increasing... read more Intraventricular hemorrhage and/or intraparenchymal hemorrhage ). Infarction of the periventricular white matter (periventricular leukomalacia) may also occur for reasons that are incompletely understood. Hypotension, inadequate or unstable brain perfusion, and blood pressure peaks (as when fluid or colloid is given rapidly IV) may contribute to cerebral infarction or hemorrhage. Periventricular white matter injury is a major risk factor for cerebral palsy Cerebral Palsy (CP) Cerebral palsy refers to a group of nonprogressive conditions characterized by impaired voluntary movement or posture and resulting from prenatal developmental malformations or perinatal or... read more and neurodevelopmental delays.

Preterm infants, particularly those with a history of sepsis Neonatal Sepsis Neonatal sepsis is invasive infection, usually bacterial, occurring during the neonatal period. Signs are multiple, nonspecific, and include diminished spontaneous activity, less vigorous sucking... read more , necrotizing enterocolitis Necrotizing Enterocolitis Necrotizing enterocolitis is an acquired disease, primarily of preterm or sick neonates, characterized by mucosal or even deeper intestinal necrosis. It is the most common gastrointestinal emergency... read more Necrotizing Enterocolitis , hypoxia, and intraventricular and/or periventricular hemorrhages or leukomalacia, are at risk of developmental and cognitive delays (see also Childhood Development Childhood Development Descriptions of development are often divided into specific domains, such as gross motor, fine motor, language, cognition, and social/emotional growth. These designations are useful, but substantial... read more ). These infants require careful follow-up during the first year of life to identify auditory, visual, and neurodevelopmental delays. Careful attention must be paid to developmental milestones Developmental Milestones* Developmental Milestones* , muscle tone, language skills Language and Speech Development Descriptions of development are often divided into specific domains, such as gross motor, fine motor, language, cognition, and social/emotional growth. These designations are useful, but substantial... read more , and growth Physical Growth of Infants and Children Physical growth includes attainment of full height and appropriate weight and an increase in size of all organs (except lymphatic tissue, which decreases in size). Growth from birth to adolescence... read more (weight Weight Physical growth includes attainment of full height and appropriate weight and an increase in size of all organs (except lymphatic tissue, which decreases in size). Growth from birth to adolescence... read more , length Length Physical growth includes attainment of full height and appropriate weight and an increase in size of all organs (except lymphatic tissue, which decreases in size). Growth from birth to adolescence... read more , and head circumference Head Circumference Physical growth includes attainment of full height and appropriate weight and an increase in size of all organs (except lymphatic tissue, which decreases in size). Growth from birth to adolescence... read more ). Infants with identified delays in visual skills should be referred to a pediatric ophthalmologist. Infants with auditory and neurodevelopmental delays (including increased muscle tone and abnormal protective reflexes) should be referred to early intervention programs that provide physical, occupational, and speech therapy. Infants with severe neurodevelopmental problems may need to be referred to a pediatric neurologist or neurodevelopmental pediatrician.

Ocular

Ocular complications include

Retinal vascularization is not complete until near term. Preterm delivery and the therapies needed to treat it (eg, supplemental oxygen) may interfere with the normal vascularization process, resulting in abnormal vessel development and sometimes defects in vision including blindness. Incidence of ROP is inversely proportional to gestational age. Disease usually manifests between 32 weeks and 34 weeks of gestational age.

Incidence of myopia and strabismus increases independently of ROP.

Infectious

Pulmonary

Pulmonary complications include

Surfactant production is often inadequate to prevent alveolar collapse and atelectasis, which result in respiratory distress syndrome (hyaline membrane disease). Many other factors can contribute to respiratory distress in the first week of life. Regardless of the cause, many extremely preterm and very preterm infants have persistent respiratory distress and an ongoing need for respiratory support. Some infants are successfully weaned off support over a few weeks; others develop chronic lung disease (bronchopulmonary dysplasia) with need for prolonged respiratory support using a high-flow nasal cannula, continuous positive airway pressure Continuous Positive Airway Pressure (CPAP) Initial stabilization maneuvers include mild tactile stimulation, head positioning, and suctioning of the mouth and nose followed as needed by Supplemental oxygen Continuous positive airway... read more (CPAP) or other noninvasive ventilatory assistance, or mechanical ventilation Mechanical Ventilation Initial stabilization maneuvers include mild tactile stimulation, head positioning, and suctioning of the mouth and nose followed as needed by Supplemental oxygen Continuous positive airway... read more . Respiratory support may be given with room air or with supplemental oxygen. If supplemental oxygen is required, the lowest oxygen concentration that can maintain target oxygen saturation levels of 90 to 95% should be used (see table ).

In addition, the American College of Obstetricians and Gynecologists recommends maternal RSV vaccination between 32 and 36 6/7 weeks of gestation, if birth is expected during the RSV season, to prevent RSV lower respiratory tract infection in infants (1 Complications references An infant born before 37 weeks of gestation is considered preterm. In 2021 in the United States, 10.48% of births were preterm ( 1), and in 2018, 26.53% of births were early term (significantly... read more ). However, it is uncertain whether maternal RSV vaccination will benefit many preterm infants because timing of birth may not allow timely administration of the vaccine.

Gastrointestinal

Gastrointestinal complications include

  • Feeding intolerance, with increased risk of aspiration

  • Necrotizing enterocolitis

Feeding intolerance is extremely common because preterm infants have a small stomach, immature sucking and swallowing reflexes, and inadequate gastric and intestinal motility. These factors hinder the ability to tolerate both oral and nasogastric feedings and create a risk of aspiration. Feeding tolerance usually increases over time.

Necrotizing enterocolitis Necrotizing Enterocolitis Necrotizing enterocolitis is an acquired disease, primarily of preterm or sick neonates, characterized by mucosal or even deeper intestinal necrosis. It is the most common gastrointestinal emergency... read more Necrotizing Enterocolitis usually manifests with bloody stool, feeding intolerance, and a distended, tender abdomen. Necrotizing enterocolitis is the most common surgical emergency in the preterm infant. Complications of neonatal necrotizing enterocolitis include bowel perforation with pneumoperitoneum, intra-abdominal abscess formation, stricture formation, short bowel syndrome, septicemia, and death.

Cardiac

The overall incidence of structural congenital heart defects among preterm infants is low. The most common cardiac complication is

The ductus arteriosus is more likely to fail to close after birth in preterm infants. The incidence of PDA increases with increasing prematurity; PDA occurs in almost half of infants whose birthweight is < 1750 g and in about 80% of those < 1000 g. About one third to one half of infants with PDA have some degree of heart failure. Preterm infants 29 weeks of gestation at birth who have respiratory distress syndrome Respiratory Distress Syndrome in Neonates Respiratory distress syndrome is caused by pulmonary surfactant deficiency in the lungs of neonates, most commonly in those born at < 37 weeks gestation. Risk increases with degree of prematurity... read more have a 65 to 88% risk of a symptomatic PDA. If infants are ≥ 30 weeks of gestation at birth, the ductus closes spontaneously in 98% by the time of hospital discharge.

Renal

Renal complications include

Renal function is limited, so the concentrating and diluting limits of urine are decreased.

Late metabolic acidosis and growth failure may result from the immature kidneys’ inability to excrete fixed acids, which accumulate with high-protein formula feedings and as a result of bone growth. Sodium and bicarbonate are lost in the urine.

Metabolic

Metabolic complications include

  • Hypoglycemia and hyperglycemia

  • Hyperbilirubinemia

  • Metabolic bone disease (osteopenia of prematurity)

  • Congenital hypothyroidism

Hyperbilirubinemia Neonatal Hyperbilirubinemia Jaundice is a yellow discoloration of the skin and eyes caused by hyperbilirubinemia (elevated serum bilirubin concentration). The serum bilirubin level required to cause jaundice varies with... read more occurs more commonly in the preterm as compared to the term infant, and kernicterus Kernicterus Kernicterus is brain damage caused by unconjugated bilirubin deposition in basal ganglia and brain stem nuclei. Normally, bilirubin bound to serum albumin stays in the intravascular space. However... read more (brain damage caused by hyperbilirubinemia) may occur at serum bilirubin levels as low as 10 mg/dL (170 micromol/L) in small, sick, preterm infants. The higher bilirubin levels may be partially due to hepatic excretion mechanisms that are inadequately developed for extrauterine life, including deficiencies in the uptake of bilirubin from the serum, its hepatic conjugation to bilirubin diglucuronide, and its excretion into the biliary tree. Decreased intestinal motility enables more bilirubin diglucuronide to be deconjugated within the intestinal lumen by the luminal enzyme beta-glucuronidase, thus permitting increased reabsorption of unconjugated bilirubin (enterohepatic circulation of bilirubin). Conversely, early feedings increase intestinal motility and reduce bilirubin reabsorption and can thereby significantly decrease the incidence and severity of physiologic jaundice. Uncommonly, delayed clamping of the umbilical cord (which has several benefits and is generally recommended) may increase the risk of hyperbilirubinemia by allowing the transfusion of RBCs thus increasing RBC breakdown and bilirubin production.

Metabolic bone disease with osteopenia is common, particularly in extremely preterm infants. It is caused by inadequate intake of calcium, phosphorus, and vitamin D and is exacerbated by administration of diuretics and corticosteroids. Breast milk also has insufficient calcium and phosphorus and must be fortified. Supplemental vitamin D is necessary to optimize intestinal absorption of calcium and control urinary excretion.

Congenital hypothyroidism Hypothyroidism in Infants and Children Hypothyroidism is thyroid hormone deficiency. Symptoms in infants include poor feeding and growth failure; symptoms in older children and adolescents are similar to those of adults but also... read more , characterized by low thyroxine (T4) and elevated thyroid-stimulating hormone (TSH) levels, is much more common among preterm infants than full-term infants. In infants with a birthweight of < 1500 g, the rise in TSH may be delayed for several weeks, necessitating repeated screening for detection. Transient hypothyroxinemia, characterized by low T4 and normal TSH levels, is very common among extremely preterm infants; treatment with L-thyroxine is not beneficial (2 Complications references An infant born before 37 weeks of gestation is considered preterm. In 2021 in the United States, 10.48% of births were preterm ( 1), and in 2018, 26.53% of births were early term (significantly... read more ).

Temperature regulation

The most common temperature regulation complication is

Preterm infants have an exceptionally large body surface area to volume ratio. Therefore, when exposed to temperatures below the neutral thermal environment, they rapidly lose heat and have difficulty maintaining body temperature. The neutral thermal environment is the environmental temperature at which metabolic demands (and thus calorie expenditure) to maintain normal body temperature (36.5 to 37.5° C rectal) are lowest.

Complications references

Diagnosis of Prematurity

  • Obstetric history and postnatal physical parameters

  • Fetal ultrasonography

  • Screening tests for complications

A diagnosis of prematurity depends on the best estimate of gestational age Gestational Age Gestational age and growth parameters help identify the risk of neonatal pathology. Gestational age is the primary determinant of organ maturity. Neonatal gestational age is usually defined... read more . Neonatal gestational age is usually defined by counting the number of weeks between the first day of the mother's last normal menstrual period and the date of delivery. However, determining gestational age based on the last menstrual period may be inaccurate if a pregnant patient has irregular menses. Alternatively, sometimes the approximate or exact date of conception is known if ovulation tests or assisted reproductive technologies were used. Also, based on the first fetal ultrasound in a pregnancy, the estimated gestational age may be changed if the ultrasonographic results differ sufficiently from the menstrual dating. After delivery, newborn physical examination findings also allow clinicians to estimate gestational age, which can be confirmed by the .

Along with appropriate testing for any identified problems or disorders, routine evaluations include pulse oximetry, complete blood count, electrolytes, bilirubin level, blood culture, serum calcium, alkaline phosphatase, and phosphorus levels (to screen for osteopenia of prematurity), hearing evaluation, cranial ultrasonography (to screen for intraventricular hemorrhage and periventricular leukomalacia), and screening by an ophthalmologist for retinopathy of prematurity (depending on gestational age). Weight should be obtained and plotted on a growth chart every day. Length and head circumference should be plotted on an appropriate growth chart at weekly intervals. Head circumference should be obtained more often, sometimes daily, if hydrocephalus Diagnosis Hydrocephalus is accumulation of excessive amounts of cerebrospinal fluid, causing cerebral ventricular enlargement and/or increased intracranial pressure. Manifestations can include enlarged... read more Diagnosis is a concern.

As with older neonates, routine newborn screening tests Screening Tests for Newborns Screening recommendations for newborns vary by clinical context and regulatory requirements. In the United States, the Health Resources & Services Administration recommends screening for all... read more are done at 24 to 48 hours of age. Unlike full-term infants, preterm infants, especially extremely preterm infants, have a high rate of false-positive results (1 Diagnosis reference An infant born before 37 weeks of gestation is considered preterm. In 2021 in the United States, 10.48% of births were preterm ( 1), and in 2018, 26.53% of births were early term (significantly... read more ). Mild elevations of several amino acids and abnormal acylcarnitine profiles are common and slight elevations of 17-hydroxyprogesterone levels and low thyroxine (T4) levels (typically with normal thyroid-stimulating hormone levels) are often present. Extremely preterm infants and very preterm infants are at risk of a delayed presentation of congenital hypothyroidism and should be periodically screened.

X-rays, often obtained for other reasons, may provide evidence of osteopenia and/or unsuspected fractures. DXA scanning Dual-energy x-ray absorptiometry (DXA) Osteoporosis is a progressive metabolic bone disease that decreases bone mineral density (bone mass per unit volume), with deterioration of bone structure. Skeletal weakness leads to fractures... read more Dual-energy x-ray absorptiometry (DXA) and quantitative ultrasonography scanning may detect osteopenia but are not in widespread use.

Diagnosis reference

Preterm, Very Preterm, and Extremely Preterm Infants

A preterm infant is an infant born before 37 weeks of gestation. Very preterm infants are 28 to 31 6/7 weeks. Extremely preterm infants are < 28 weeks.

Complications

The incidence and severity of complications of preterm infants Complications An infant born before 37 weeks of gestation is considered preterm. In 2021 in the United States, 10.48% of births were preterm ( 1), and in 2018, 26.53% of births were early term (significantly... read more increase with decreasing gestational age and birthweight. Some complications (eg, necrotizing enterocolitis Necrotizing Enterocolitis Necrotizing enterocolitis is an acquired disease, primarily of preterm or sick neonates, characterized by mucosal or even deeper intestinal necrosis. It is the most common gastrointestinal emergency... read more Necrotizing Enterocolitis , retinopathy of prematurity Retinopathy of Prematurity Retinopathy of prematurity is a bilateral disorder of abnormal retinal vascularization in premature infants, especially those of lowest birth weight. Outcomes range from normal vision to blindness... read more , bronchopulmonary dysplasia Bronchopulmonary Dysplasia (BPD) Bronchopulmonary dysplasia is chronic lung disease of the neonate that typically is caused by prolonged ventilation and is further defined by degree of prematurity and extent of supplemental... read more Bronchopulmonary Dysplasia (BPD) , intraventricular hemorrhage Intraventricular hemorrhage and/or intraparenchymal hemorrhage The forces of labor and delivery occasionally cause physical injury to the infant. The incidence of neonatal injury resulting from difficult or traumatic deliveries is decreasing due to increasing... read more Intraventricular hemorrhage and/or intraparenchymal hemorrhage ) occur primarily in infants delivered at < 34 weeks.

Symptoms and Signs

The preterm infant is small, usually weighing < 2.5 kg, and tends to have thin, shiny, pink skin through which the underlying veins are easily seen. Little subcutaneous fat, hair, or external ear cartilage exists. Spontaneous activity and tone are reduced, and extremities are not held in the flexed position typical of term infants.

In males, the scrotum may have few rugae, and the testes may be undescended. In females, the labia majora do not yet cover the labia minora.

Reflexes develop at different times during gestation. The Moro reflex begins by 28 to 32 weeks of gestation and is well established by 37 weeks. The palmar reflex starts at 28 weeks and is well established by 32 weeks. The tonic neck reflex starts at 35 weeks and is most prominent at 1 month postterm.

Evaluation

  • Monitoring in a neonatal intensive care unit (NICU)

  • Screening for complications

NICU monitoring and screening

Serial physical examinations are important in monitoring infants' progress and detecting new problems (eg, respiratory problems, jaundice). Frequent weight assessments are necessary to optimize weight-based medication dosages and feeding.

Intraventricular hemorrhage Intraventricular hemorrhage and/or intraparenchymal hemorrhage The forces of labor and delivery occasionally cause physical injury to the infant. The incidence of neonatal injury resulting from difficult or traumatic deliveries is decreasing due to increasing... read more Intraventricular hemorrhage and/or intraparenchymal hemorrhage in extremely preterm infants may be clinically silent, and a routine cranial ultrasound is recommended for these infants. The incidence of IVH decreases with increasing gestational age, so routine screening of preterm infants > 32 weeks is not considered useful unless they had significant complications. Most IVHs occur in the first week of life and, unless there are clinical indications of hemorrhage, the highest yield is obtained by scanning at 7 to 10 days of age. Extremely preterm infants are at risk of periventricular leukomalacia, which may develop later in the course (with or without hemorrhage), so they should have cranial ultrasonography at 6 weeks of age. Infants with moderate or severe hemorrhages should be followed using head circumference measurements and periodic cranial ultrasonography to detect and monitor hydrocephalus; there is no benefit in repeat scanning of infants with minor hemorrhage without clinical indication (1 Evaluation reference An infant born before 37 weeks of gestation is considered preterm. In 2021 in the United States, 10.48% of births were preterm ( 1), and in 2018, 26.53% of births were early term (significantly... read more ). However, close neurodevelopmental follow-up is recommended for infants who have any hemorrhage.

Later screening

Screening for retinopathy of prematurity Retinopathy of Prematurity Retinopathy of prematurity is a bilateral disorder of abnormal retinal vascularization in premature infants, especially those of lowest birth weight. Outcomes range from normal vision to blindness... read more is recommended for infants born ≤ 1500 g or ≤ 30 weeks of gestational age and for larger and more mature infants who have had an unstable clinical course. The first examination is done according to a schedule based on the infant's gestational age (see table ). Examinations are usually repeated at 1- to 3-week intervals depending on the initial findings and are continued until the retina is mature. Some of these follow-up examinations are done after the infant is discharged. The use of digital photographic retinal images is an alternate method of examination and follow-up in areas where a skilled examiner is not routinely available.

Table

Screening for Retinopathy of Prematurity

Gestational Age* at Birth

Gestational Age* at First Examination

Postmenstrual

Chronologic

22 weeks

31 weeks

9 weeks

23 weeks

31 weeks

8 weeks

24 weeks

31 weeks

7 weeks

25 weeks

31 weeks

6 weeks

26 weeks

31 weeks

5 weeks

27 weeks

31 weeks

4 weeks

28 weeks

32 weeks

4 weeks

29 weeks

33 weeks

4 weeks

30 weeks

34 weeks

4 weeks

Older gestational age, high-risk factors†

Not applicable

4 weeks

* Postmenstrual gestational age.

† Some of high-risk factors include, eg, infants with hypotension requiring inotropic support, infants who received oxygen supplementation for more than a few days, and infants who received oxygen without saturation monitoring.

Data from Fierson WM, American Academy of Pediatrics Section on Ophthalmology, American Academy of Ophthalmology, American Association for Pediatric Ophthalmology and Strabismus, American Association of Certified Orthoptists: Screening examination of premature infants for retinopathy of prematurity. Pediatrics 142(6):e20183061, 2018. doi: 10.1542/peds.2018-3061

Evaluation reference

Treatment of Preterm Infants

  • Supportive care

Specific disorders are treated as discussed elsewhere in THE MANUAL.

General supportive care of the preterm infant is best provided in a NICU or special care nursery and involves careful attention to the thermal environment, using servo-controlled incubators. Scrupulous adherence is paid to handwashing before and after all patient contact. Infants are continually monitored for apnea, bradycardia, and hypoxemia until 35 weeks of gestation.

Parents should be encouraged to visit and interact with the infant as much as possible within the constraints of the infant’s medical condition. Skin-to-skin contact between the infant and parent (kangaroo care) is beneficial for infant health and facilitates parental bonding. It is feasible and safe even when infants are supported by ventilators and infusions.

Feeding

Feeding should be by nasogastric tube until coordination of sucking, swallowing, and breathing is established at about 34 weeks of gestation, at which time breastfeeding Breastfeeding (See also Nutrition in Infants.) Breast milk is the nutrition of choice for young infants. The American Academy of Pediatrics (AAP) recommends exclusive breastfeeding for a minimum of 6 months... read more is strongly encouraged. Most preterm infants tolerate breast milk, which provides immunologic and nutritional factors that are absent in cow’s milk formulas. However, breast milk does not provide sufficient calcium, phosphorus, and protein for very low-birthweight infants (ie, < 1500 g), for whom it should be mixed with a breast milk fortifier. Alternatively, specific preterm infant formulas that contain 20 to 24 kcal/oz (2.8 to 3.3 joules/mL) can be used.

In the initial 1 or 2 days, if adequate fluids and calories cannot be given by mouth or nasogastric tube because of the infant’s condition, IV parenteral nutrition with protein, glucose, and fats is given to prevent dehydration and undernutrition. Breast milk or preterm formula feeding via nasogastric tube can satisfactorily maintain caloric intake in small, sick, preterm infants, especially those with respiratory distress or recurrent apneic spells. Feedings are begun with small amounts (eg, 1 to 2 mL every 3 to 6 hours) to stimulate the gastrointestinal tract. When tolerated, the volume and concentration of feedings are slowly increased over 7 to 10 days. In very small or critically sick infants, total parenteral hyperalimentation via a peripheral IV or a percutaneously or surgically placed central catheter may be required for a prolonged period of time until full enteral feedings can be tolerated.

Hospital discharge

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

  • Taking an adequate amount of formula and/or breast milk without special assistance

  • Gaining weight steadily

  • Able to maintain a normal body temperature in a crib

  • No longer having apnea or bradycardia requiring intervention

Most preterm infants are ready to go home when they are at 35 to 37 weeks of gestational age and weigh 2 to 2.5 kg. However, there is wide variation. Some infants are ready for discharge earlier and some require longer stays in the hospital. The length of time the infant stays in the hospital does not affect the long-term prognosis.

Preterm infants should be transitioned to the supine sleeping position before hospital discharge. Parents should be instructed to keep cribs free of fluffy materials including blankets, quilts, pillows, and stuffed toys, which have been associated with an increased risk of sudden unexplained infant death Sudden Unexpected Infant Death (SUID) and Sudden Infant Death Syndrome (SIDS) Sudden unexpected infant death (SUID) is a term used to describe any unexpected and sudden death in a child less than 1 year of age, which often occurs during sleep or in the infant's sleep... read more (SUID).

Because preterm infants are at risk of apnea, oxygen desaturation, and bradycardia while in a car seat, the American Academy of Pediatrics currently recommends that before discharge all preterm infants have their oxygen saturation monitored for 90 to 120 minutes while seated in the car seat that they will use after discharge. However, there are no agreed-upon criteria for passing or failing the test, and a recent report from the Canadian Paediatric Society (CPS) found that the car seat test had poor reproducibility and did not predict risk of mortality or neurodevelopmental delay. Thus, the CPS does not recommend routine testing before discharge (1 Evaluation reference An infant born before 37 weeks of gestation is considered preterm. In 2021 in the United States, 10.48% of births were preterm ( 1), and in 2018, 26.53% of births were early term (significantly... read more ). Given the concerns about the car seat test, a common-sense approach to car travel is for a newly discharged preterm infant to be observed by a non-driving adult during all car seat travel until the infant has reached the due date and has remained consistently able to tolerate being in the car seat. Because the infant's color needs to be observed, travel should be limited to daylight hours. Long trips should be broken up into 45- to 60-minute segments so that the infant 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 only be given by a certified car seat expert.

After discharge, extremely preterm and very preterm infants should receive careful neurodevelopmental follow-up and appropriate early referral to intervention programs as needed for physical, occupational, and language therapy.

Treatment references

Prognosis for Preterm Infants

Prognosis varies with presence and severity of complications, or the presence of multiple births, but usually mortality and likelihood of intellectual disability and other complications decrease greatly with increasing gestational age and birthweight (see table ).

Table

Prevention of Preterm Delivery

Although early and appropriate prenatal care is important overall, there is no good evidence that such care or any other interventions decrease the incidence of preterm birth.

The use of tocolytics to arrest preterm labor and provide time for prenatal administration of corticosteroids to hasten lung maturation is discussed elsewhere (see Preterm Labor Treatment Labor (contractions resulting in cervical change) that begins before 37 weeks gestation is considered preterm. Risk factors include prelabor rupture of membranes, uterine abnormalities, infection... read more ).

Key Points

  • There are many risk factors for preterm birth, but they are not present in most cases.

  • Complications include hypothermia, hypoglycemia, respiratory distress syndrome, apneic episodes, intraventricular hemorrhage, developmental delay, sepsis, retinopathy of prematurity, hyperbilirubinemia, necrotizing enterocolitis, and poor feeding.

  • Mortality and likelihood of complications decrease greatly with increasing gestational age and birthweight.

  • Treat disorders and support body temperature and feeding.

  • Although women who have consistent prenatal care have a lower incidence of preterm birth, there is no evidence that improved prenatal care or other interventions decrease the incidence of preterm birth.

More Information

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

Late Preterm Infants

An infant born between 34 and 36 6/7 weeks of gestation is considered late preterm.

Complications of Late Preterm Infants

Although clinicians tend to focus on the more dramatic and obvious manifestations of problems of infants born < 34 weeks of gestation, late preterm infants are at risk of many of the same disorders (see complications of preterm infants Complications An infant born before 37 weeks of gestation is considered preterm. In 2021 in the United States, 10.48% of births were preterm ( 1), and in 2018, 26.53% of births were early term (significantly... read more ). Compared to term infants, they have longer hospital stays and higher incidence of readmission and diagnosed medical disorders. Most complications relate to dysfunction of immature organ systems and are similar to, but typically less severe than, those of infants born more prematurely. However, some complications of prematurity (eg, necrotizing enterocolitis Necrotizing Enterocolitis Necrotizing enterocolitis is an acquired disease, primarily of preterm or sick neonates, characterized by mucosal or even deeper intestinal necrosis. It is the most common gastrointestinal emergency... read more Necrotizing Enterocolitis , retinopathy of prematurity Retinopathy of Prematurity Retinopathy of prematurity is a bilateral disorder of abnormal retinal vascularization in premature infants, especially those of lowest birth weight. Outcomes range from normal vision to blindness... read more , bronchopulmonary dysplasia Bronchopulmonary Dysplasia (BPD) Bronchopulmonary dysplasia is chronic lung disease of the neonate that typically is caused by prolonged ventilation and is further defined by degree of prematurity and extent of supplemental... read more Bronchopulmonary Dysplasia (BPD) , intraventricular hemorrhage Intraventricular hemorrhage and/or intraparenchymal hemorrhage The forces of labor and delivery occasionally cause physical injury to the infant. The incidence of neonatal injury resulting from difficult or traumatic deliveries is decreasing due to increasing... read more Intraventricular hemorrhage and/or intraparenchymal hemorrhage ) are uncommon in late preterm infants. In most cases, complications resolve completely.

Complications more common among late preterm infants include the following:

Evaluation of Late Preterm Infants

  • Routine screening for complications

There are variations in practice in the care of late preterm infants, particularly with respect to the gestational age and/or birthweight at which infants are routinely admitted to a NICU. Some hospitals routinely admit infants < 35 weeks of gestation to the NICU, whereas others may have a cutoff of < 34 weeks. Still other hospitals have a discretionary approach. Regardless of the location of the infant, all late preterm infants need close monitoring of the following:

  • Temperature: There is a high risk of hypothermia, and some late preterm infants may need to be in an incubator. The infant's temperature should be routinely assessed. For infants who are in the mother's hospital room, the temperature of the room should be maintained at 22 to 25° C (72 to 77° F), similar to that recommended for newborn care areas.

  • Weight: Depending on the infant's intake, there may be excessive weight loss, dehydration, and hypernatremia. The infant should be weighed daily and the percent weight loss should be calculated and tracked. Electrolytes should be checked if the weight loss exceeds 10%.

  • Feedings and intake: Late preterm infants may breastfeed or bottle feed poorly and take insufficient amounts of milk. Nasogastric feeding assistance is commonly needed, particularly in infants who are < 34 weeks of gestation. Because the mother's milk may take 1 to 4 days to come in, supplementation with donor milk or formula may be necessary. The amount of milk that the infant receives as well as either the number of wet diapers or the urine output (calculated as mL/kg/hour) should be tracked.

  • Glucose: Early hypoglycemia (within the first 12 hours of life) is common, so early feeding and blood glucose screening as recommended by the American Academy of Pediatrics (1 Evaluation reference An infant born before 37 weeks of gestation is considered preterm. In 2021 in the United States, 10.48% of births were preterm ( 1), and in 2018, 26.53% of births were early term (significantly... read more ) for the first 24 hours of life should be done. In addition, some experts recommend continued screening every 12 hours until discharge to detect infants with hypoglycemia due to insufficient milk intake.

Evaluation reference

Treatment of Late Preterm Infants

  • Supportive care

  • Specific treatment for complications

Identified disorders are treated. For infants without specific conditions, support is focused on body temperature and feeding.

Late preterm infants can be stressed by the metabolic demands of maintaining a normal core temperature of 36.5 to 37.5° C (97.7 to 99.5° F), which roughly corresponds to an axillary temperature of 36.5 to 37.3° C (97.7 to 99.1° F). The environmental temperature at which metabolic demands (and thus calorie expenditure) to maintain body temperature in the normal range are lowest is the thermoneutral temperature. A normal core temperature can be maintained at lower environmental temperatures at the cost of increased metabolic activity, so a normal core temperature is no assurance that the environmental temperature is adequate. Once the core temperature falls below normal, the environmental temperature is below what is called the thermoregulatory range and therefore far below the thermoneutral range. In clinical practice, a room with a temperature of 22.2 to 25.6° C (72 to 78° F) combined with skin-to-skin contact under blankets, swaddling with multiple blankets, and wearing a hat may provide a thermoneutral environment for a large and somewhat more mature late preterm infant. Smaller and less mature late preterm infants usually require an incubator for a period of time to provide a thermoneutral environment.

Breastfeeding Breastfeeding (See also Nutrition in Infants.) Breast milk is the nutrition of choice for young infants. The American Academy of Pediatrics (AAP) recommends exclusive breastfeeding for a minimum of 6 months... read more is strongly encouraged. Breast milk, which provides immunologic and nutritional factors that are absent in cow’s milk formulas, is well tolerated by late preterm infants. If infants do not suck and/or swallow adequately, feedings should be given by nasogastric gavage beginning with small amounts and gradually increasing over time.

Prognosis for Late Preterm Infants

Prognosis varies with presence and severity of complications. In general, mortality and the likelihood of complications decrease greatly with increasing gestational age and birthweight.

Respiratory issues typically resolve without long-term sequelae. Apneic episodes typically resolve when infants reach the age at which they would have been by 37 to 38 weeks of gestation and almost always by 43 weeks.

Prognosis reference

  • 1. Woythaler M: Neurodevelopmental outcomes of the late preterm infant. Semin Fetal Neonatal Med 24(1):54-59, 2019. doi: 10.1016/j.siny.2018.10.002

Key Points

  • Although late preterm infants (born between ≥ 34 weeks and < 36 6/7 weeks of gestation) may appear to be similar in size and appearance to term infants, they are at increased risk of complications.

  • Complications include hypothermia, hypoglycemia, poor feeding, excessive weight loss, respiratory distress, hyperbilirubinemia, and an increased likelihood of readmission after discharge.

  • Treat disorders and support body temperature and feeding.

  • Monitor neurodevelopmental status and provide appropriate referral to address any disabilities.

Drugs Mentioned In This Article

Drug Name Select Trade
BEYFORTUS
Synagis
Calcidol, Calciferol, D3 Vitamin, DECARA, Deltalin, Dialyvite Vitamin D, Dialyvite Vitamin D3, Drisdol, D-Vita, Enfamil D-Vi-Sol, Ergo D, Fiber with Vitamin D3 Gummies Gluten-Free, Happy Sunshine Vitamin D3, MAXIMUM D3, PureMark Naturals Vitamin D, Replesta, Replesta Children's, Super Happy SUNSHINE Vitamin D3, Thera-D 2000, Thera-D 4000, Thera-D Rapid Repletion, THERA-D SPORT, UpSpring Baby Vitamin D, UpSpring Baby Vitamin D3, YumVs, YumVs Kids ZERO, YumVs ZERO
View PATIENT EDUCATION
NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
quiz link

Test your knowledge

Take a Quiz! 
iOS ANDROID
iOS ANDROID
iOS ANDROID
TOP