Neonatal Adaptation and Birth Stress

Birth stress and endocrine response

The birth process is a serious biomechanical test for the fetus, acting as a powerful stressor. This stress triggers a cascade reaction of hormonal systems necessary for survival in new conditions.

In the very first hours of life, the sympathoadrenal and pituitary systems are activated:

• There is a massive release of catecholamines and glucocorticoids.
• This stimulates the production of tropic hormones (TSH, ACTH) and thyroxine.
• High levels of glucocorticoids in the infant's blood are due to the functioning of the single "mother–placenta–fetus" system and the supply of hormones from the mother.
• Due to the maturity of the thyroid gland, the newborn undergoes a short-term state of physiological hyperthyroidism.

Respiratory system and first breath

For the lungs to begin functioning, they need to be cleared of fetal fluid and filled with air (aeration). The trigger for the first breath is the peak concentration of catecholamines.

Lung clearance proceeds in two stages:

1. Mechanical: part of the fluid is simply squeezed out by the compression of the chest in the birth canal.
2. Resorptive: fluid remnants are absorbed into the blood within two hours under the influence of adrenaline.

Aeration takes only a few minutes. To prevent the lungs from collapsing, surfactant is required — a substance whose synthesis begins as early as the 2nd trimester of intrauterine development.

Hemodynamic restructuring

With the onset of breathing, pulmonary circulation is activated, pressure in its vessels drops, and systemic vascular resistance increases.

The transition to extrauterine circulation is accompanied by the closure of fetal communications:

• Ductus arteriosus (ductus arteriosus Botalli) spasms due to oxygen and closes within 24–48 hours.
• Foramen ovale (foramen ovale) closes functionally by 3 months, and anatomically obliterates by one year.
• Ductus venosus (ductus venosus) gradually transforms into the ligamentum teres hepatis (ligamentum teres hepatis) by the end of the second week.

In the first 1–2 days, transitional circulation is observed with blood shunting through still open ducts and the foramen.

Metabolism and homeostasis

Immediately after birth, the kidneys become involved in maintaining the internal environment, driven by decreased vascular resistance and increased renal blood flow. General immaturity and birth stress determine metabolic features:

• Glycolytic (anaerobic) energy metabolism temporarily predominates.
• Transitory acidosis occurs (pH recovers by the end of the 1st day).
• Hypoglycemia and hyperketonemia are typical in the first hours and days.
• Hypocalcemia and hypomagnesemia develop during the first two days.

Later, the catabolic phase is replaced by an anabolic one: the child begins to intensively gain weight and develop.

Class and exam questions

What else to study on this topic

• Stages and mechanisms of fetal fluid resorption from the lungs
• Hormonal profile of the newborn in the first hours of life (role of ACTH and TSH)
• Hemodynamic shunts in transitional circulation
• Phases of metabolic adaptation: from catabolism to anabolism

Other topics in «Chapter 2. Neonatology»

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