Transitory Conditions of Newborns

Weight dynamics and metabolism

Loss of initial body weight is a normal process observed in all infants, regardless of birth weight. Maximum weight loss occurs on days 3–4 (sometimes on day 5). For a term infant, the upper limit of the norm is no more than 6–7%. The baseline weight is usually regained by days 6–7 of life, at the latest by day 10.

Pathogenesis of weight loss:

• Energy deficit: physiological underfeeding in the first days causes enhanced catabolism of endogenous fats.
• Fluid deficit: insufficient fluid intake combined with physiological losses (meconium passage, diuresis, respiratory perspiratory loss).

Temperature irregularities (hypothermia, overheating) and dry air in the ward exacerbate fluid loss. Medical intervention is not required; the main management tactic is feeding on demand at the mother's breast.

Regarding the metabolic profile, the first days of life are characterized by a combination of hypoglycemia (decreased glucose levels) and hyperketonemia (increased ketone body levels).

Transitional intestinal catarrh

This condition, also known as physiological dyspepsia, reflects the process of microbiome establishment. Initial colonization begins during childbirth via the birth canal flora and then continues through breast milk. Early breastfeeding is critical: mother's milk serves as the primary source of bifidobacteria.

Phases of intestinal colonization:

1. Aseptic phase: the first 10–20 hours.
2. Phase of initial colonization: days 3–5. Characterized by mixed flora (bifidobacteria, cocci, fungi).
3. Phase of transformation: 2nd week of life. Stabilization of the microbiome occurs with a dominance of bifidobacteria.

During the first two days, meconium (initial stool) is passed. On the 3rd day, the stool becomes transitional: bowel movements become more frequent, containing curds, mucus, and watery spots on the diaper. Microscopy reveals fatty acids and an increased number of leukocytes (up to 30 per high-power field). From days 3–4, mature stool forms: it acquires a yellow color, pasty consistency, and the leukocyte count drops to 12–20. Normally, the frequency of bowel movements in the neonatal period is 3–5 times per day.

Thermal balance disorders

In newborns, heat loss processes dominate over heat production, predisposing them to transitional temperature shifts.

• Transitional hypothermia: occurs due to the sharp temperature change at birth. For prevention, the infant is placed on the mother's abdomen and covered with a warm sterile blanket (this blocks amniotic fluid evaporation). Spontaneous temperature stabilization (homeothermy) occurs by the middle of the first day.
• Transitional hyperthermia: develops on days 3–5. Causes are multifactorial: predominance of catabolism, "protein fever" (fluid deficiency with a protein-rich diet), hypernatremia, reaction to E. coli endotoxins during intestinal colonization, as well as simple overheating. In premature infants, hyperthermia (up to 38.5 °C) easily occurs even from incubator electric heating due to impaired heat loss. It is treated with physical cooling and oral hydration (5% dextrose/glucose, volume of about 200 g/day, but not exceeding 10% of body weight).

Renal function and hormonal crisis

Transitional features of renal function reflect the adaptation of the excretory system:

1. Oliguria: low urine output in the first 3 days due to small fluid intake volume and hemodynamic features.
2. Proteinuria (albuminuria): typical for the first days. Associated with high permeability of the renal filter, massive breakdown of red blood cells, and perinatal venous congestion.
3. Uric acid infarction: occurs in almost all infants. Manifests as the excretion of turbid red urine (leaving brownish-red spots). The cause is hemoconcentration and deposition of uric acid crystals in the tubules (from pyramids to cortex). Resolves spontaneously by the end of the first week with increased diuresis. If signs persist into the second half of the 2nd week, this is pathological.

Hormonal (sexual) crisis includes desquamative vulvovaginitis, metrorrhagia, and physiological mastopathy (breast engorgement). It is important to remember: edema of the external genitalia is not part of this transitional condition.

Class and exam questions

What else to study on this topic

• Mechanisms of microbiome formation and the role of bifidobacteria
• Differential diagnosis of physiological weight loss and pathological hypotrophy
• Features of thermoregulation in extremely premature infants
• Neonatal metabolic profile: causes of hypoglycemia and hyperketonemia

Other topics in «Chapter 2. Neonatology»

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