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Premature baby
Last reviewed: 05.07.2025
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A premature baby is a baby born before 37 weeks of gestation.
The full gestational age is 40 weeks. Children born before 37 weeks of gestation have an increased incidence of complications and mortality, which is approximately proportional to the degree of prematurity. Preterm birth is one of the main causes of neonatal morbidity and mortality.
Previously, any baby weighing less than 2.5 kg at birth was considered premature. This definition is incorrect because many babies weighing less than 2.5 kg at birth are full-term or post-term but small for their gestational age; they have different appearances and different problems. Babies weighing less than 2.5 kg at birth are considered low birth weight, and babies weighing less than 1500 g are considered very low birth weight.
What causes a baby to be born prematurely?
The cause of preterm birth with prior or premature rupture of membranes is usually unknown. However, maternal history often reveals low socioeconomic status; inadequate prenatal care; poor nutrition; low education; unmarried status; history of preterm birth; and intercurrent illnesses or infections (eg, bacterial vaginosis). Other risk factors include placental abruption and preeclampsia.
Signs of a premature baby
Physical examination findings correlate with gestational age. Prenatal ultrasound, if performed, also determines gestational age.
A premature baby is small, usually weighing less than 2.5 kg at birth, and most often has thin, shiny, pink skin through which the subcutaneous veins are easily visible. The baby has little subcutaneous fat, little hair, and weak cartilages of the outer ear. Spontaneous motor activity and muscle tone are reduced, and the limbs are not held in the flexed position typical of full-term newborns. In boys, scrotal folding may be poorly expressed, and the testicles may not descend into the scrotum. In girls, the labia minora are not yet covered by the labia majora. Reflexes develop at different times during intrauterine development. The Moro reflex begins to appear by the 28th to 32nd week of gestation and is well elicited by the 37th week of gestation. The palmar reflex begins to be elicited at the 28th week and is well elicited by the 32nd week. At 35 weeks, the tonic cervical reflex begins to appear, most clearly manifested at 1 month after birth.
Complications in premature babies
Most complications are associated with dysfunction of immature organs and systems.
Lungs
Surfactant production is often insufficient to prevent alveolar collapse and atelectasis, leading to respiratory distress syndrome.
Central nervous system
Infants born before 34 weeks of gestation have inadequate coordination of the sucking and swallowing reflexes and require parenteral nutrition or tube feeding. Immaturity of the respiratory center at the base of the brain leads to episodes of apnea (central apnea). Apnea may also result from subglottic obstruction (obstructive apnea). These two variants may be combined (mixed apnea).
The periventricular germinal matrix (embryonic cells located above the caudate nucleus on the lateral wall of the lateral ventricles, found only in the fetus) predisposes to hemorrhages that may extend into the ventricular cavity (intraventricular hemorrhage), and white matter infarctions in the periventricular area (periventricular leukomalacia) may also occur for reasons that are not fully understood. Hypotension, inadequate or unstable cerebral perfusion, and blood pressure spikes (eg, when intravenous fluids are given rapidly) may contribute to cerebral infarctions or hemorrhages.
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Infections
Sepsis or meningitis occurs approximately 4 times more often. The increased likelihood of developing infections is a consequence of the use of permanent intravascular catheters and tracheal intubation, the presence of a violation of the integrity of the skin and a significantly reduced level of immunoglobulins in the blood serum.
Thermoregulation
Premature babies have an exceptionally high surface area to mass ratio. Therefore, if the baby is in an environment with a temperature lower than neutral, he will lose heat quickly and have difficulty maintaining his body temperature.
Gastrointestinal tract
The small stomach and immaturity of the sucking and swallowing reflexes prevent oral or nasogastric feeding and create a risk of aspiration. Necrotizing enterocolitis develops very often.
Kidneys
Renal function is reduced, including concentrating function. Late metabolic acidosis and growth failure may result from the inability of immature kidneys to excrete bound acids that accumulate during high-protein feeding and as a result of bone growth. Na and HCO3 are absent from the urine.
Metabolic problems
Hypoglycemia and hyperglycemia.
Hyperbilirubinemia is more common, and scleral icterus may develop at serum bilirubin levels as low as 10 mg/dL (170 μmol/L) in small, sick, immature neonates. The higher bilirubin levels may be due in part to inadequate hepatic excretion mechanisms, including failure to uptake bilirubin from the blood, to conjugate it from the liver to bilirubin diglycuronide, and to excrete it into the biliary tract. Reduced intestinal motility allows more bilirubin diglycuronide to be deconjugated in the intestinal lumen by the enzyme beta-glucuronidase, resulting in increased reabsorption of unconjugated bilirubin (enterohepatic circulation of bilirubin). In contrast, early feeding increases intestinal motility and decreases bilirubin reabsorption and can therefore significantly reduce the incidence and severity of physiological jaundice. Rarely, late cord clamping increases the risk of significant hyperbilirubinemia because it facilitates the transfusion of large numbers of red blood cells, thus increasing red blood cell breakdown and bilirubin formation.
Treatment of diseases in premature babies
General supportive care is best provided in a neonatal intensive care unit or special care unit and includes careful attention to maintaining appropriate temperature using servo-controlled incubators; special attention to hand washing before and after all patient contact. The patient should be monitored for episodes of apnea, bradycardia, and hypoxemia until 34.5–35 weeks of gestation.
Parents should be encouraged to visit and interact with the child as much as the child's condition allows.
Feeding a premature baby
The premature infant should be fed by nasogastric tube until coordination of sucking, swallowing, and breathing is established, around 34 weeks of gestation, when breastfeeding should be encouraged. Most premature infants tolerate breast milk well, as it provides nutrients and immune protective factors that are lacking in cow's milk-based formulas. However, breast milk does not provide sufficient calcium, phosphorus, and protein for very low birth weight infants (i.e., <1500 g), for whom supplementation with breast milk is necessary. Preterm formulas containing 20-24 kcal/oz (2.8-3.3 J/ml) may be used as an alternative.
In the early days, if the infant's condition does not permit adequate fluid and caloric intake by mouth or nasogastric tube, intravenous 10% glucose and electrolyte solution may be given to prevent dehydration and malnutrition. Continuous flow of breast milk or formula via nasogastric or nasojejunal tube may satisfactorily maintain intake in small sick premature infants, especially in the presence of respiratory distress syndrome or recurrent episodes of apnea. Feedings are initiated in small amounts (eg, 1–2 mL every 3–6 hours) to stimulate the gastrointestinal tract. If tolerated, the volume and concentration are slowly increased over 7–10 days. Very small or critically ill infants may require total parenteral nutrition via a peripheral intravenous catheter or a central catheter (percutaneous or surgical) until enteral feedings are tolerated.
How to prevent the birth of a premature baby?
The risk of preterm birth can be reduced by ensuring that all women, particularly those in high-risk groups, have access to early and appropriate prenatal care, including advice on the importance of avoiding alcohol, smoking and illicit drugs.
What is the prognosis for a premature baby?
A premature baby has a variable prognosis, which varies depending on the presence and severity of complications, but generally survival increases significantly with increasing gestational age and birth weight. Babies with birth weights between 1250 g and 1500 g have a survival rate of about 95%.