Classification and criteria of prematurity
Birth weight is not an absolute criterion for the degree of prematurity, since in 20–30% of cases weight and height may correspond to a full-term infant. The most objective criterion is gestational age. However, to determine the management and nursing strategy, three weight groups are distinguished:
- LBW (low birth weight): 1500–2500 g.
- VLBW (very low birth weight): 1000–1500 g.
- ELBW (extremely low birth weight): 1000 g and below.
The etiology of preterm birth includes social and biological factors (age, nutrition, paternal smoking increases the risk of severe malformations by 2–2.5 times), burdened obstetrical and gynecological history (short interval between births, previous abortions), and maternal diseases.
External signs of immaturity (somatoscopy)
The child's appearance directly depends on the degree of immaturity. Extremely premature infants (VLBW and ELBW) are characterized by prominent marker signs:
- Skin: thinned, wrinkled, dark red (plethora), abundantly covered with fine hair (lanugo).
- Subcutaneous adipose tissue: practically absent. The proportion of brown fat is critically small — about 1% (whereas in LBW infants it is about 6%).
- Bones: cranial vault bones are pliable, sutures and lateral fontanelles are open. Auricles are flat, featureless, and tightly pressed to the skull due to cartilage underdevelopment.
- Genitalia: in boys, cryptorchidism is pronounced (scrotum is smooth, testes are not descended), in girls, the pudendal cleft gapes due to underdevelopment of the labia majora, clitoris is hypertrophied.
Neurological status and thermoregulation
The severity of the condition in extremely premature infants is determined by the functional immaturity of the central nervous and autonomic systems. Patients with LBW show only moderate hypotonia (partial flexion posture) and a slight decrease in reflexes.
In VLBW and ELBW, diffuse muscular hypotonia is observed (the child lies with extended limbs — «frog posture»), and reflexes fade to the point of areflexia. Vital reflexes (sucking and swallowing) may be absent, which requires tube feeding.
Immaturity of the thermoregulation center is extremely dangerous. Infants with ELBW are unable to maintain body temperature (poikilothermia). Due to the lack of subcutaneous adipose tissue and brown fat, they rapidly cool down to 32–34 °C, which leads to a fatal outcome without adequate care.
Physical development in the first year of life
The main pattern of development in premature infants is catch-up growth. The rates of weight and length gain are inversely proportional to birth indicators. For example, a body mass of 800–1000 g increases by 8–10 times by one year, while a weight of 2001–2500 g increases by only 4–5 times. Height by the end of the first year reaches 65–75 cm (absolute gain of 30–35 cm).
The first month is a period of complex adaptation. Physiological weight loss is more pronounced (8–12%), and its recovery is delayed (in children with a gestational age of less than 32 weeks, weight returns to initial values only by the end of the first month).
Equalization of physical parameters with peers usually occurs by 3 years of age, and in ELBW children, the process can drag on to 8–9 years. LBW children compensate for psychomotor skills by the end of the 1st year, and ELBW children by the 3rd year of life.
The rule of catch-up growth: «The smaller the start, the larger the multiplier.» A weight of 1 kg at one year is multiplied by 10, while a weight of 2.5 kg is multiplied by only 4.
Class and exam questions
Is a premature infant required to weigh less than 2500 g?
No, body weight is not an absolute criterion. In 20–30% of cases, the anthropometric data of a premature infant may correspond to a full-term baby.
How to distinguish a pathological neurological symptom from a sign of prematurity?
Symptoms like muscle hypotonia and lethargy are physiological for premature infants. However, the «setting-sun sign» or rigidity always indicate central nervous system damage.
Why are extremely premature infants prone to rapid hypothermia?
This is due to the immaturity of the thermoregulation center, the practical absence of subcutaneous adipose tissue, and the critically small proportion of brown fat (about 1%).
What else to study on this topic
- Pathogenesis of transient hyperbilirubinemia and the risk of kernicterus
- Early and late anemia of prematurity: timing of manifestation and treatment
- Characteristics of the respiratory pattern and respiratory distress syndrome
- Hemodynamic instability and patent ductus arteriosus (PDA)
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