Postnatal adaptation

Postnatal adaptation is a complex process that involves multiple adaptive changes within several organ systems. For successful transition from intrauterine to extrauterine environment, relatively rapid conversion to air breathing and blood flow changes (especially in pulmonary vascular system) must occur simultaneously.

Spontaneous breathing causes water in lungs to be resorbed into blood and lymphatic vessels, thus transforming the liquid lung environment into gaseous one. This enables alveolar gas exchange, which in turn increases partial pressure of oxygen (PaO₂) causing pulmonary vasodilation and circulation changes.

Transformation of circulation happens as the pulmonary blood flow increases while pulmonary hypertension subsides. Consequently, ductal shunting changes to left-right and increased PaO₂ causes ductus arteriosus to close. Transition is very fast (within seconds to minutes) as a newborn cries, pinks up and then starts to have regular and calm breathing pattern.

Adequate blood volume is necessary to facilitate adaptive processes and ensure sufficient oxygen transport and organ/tissue perfusion. Placental transfusion may be considered in order to enhance arterial oxygen content, increasing cardiac output, and improving oxygen delivery.

It involves a shift of placental blood to the neonate immediately after delivery and may be achieved in two different ways: delayed cord clamping and umbilical cord milking. These techniques can help to achieve a greater blood volume at birth (increase of up to 10–15 ml/kg), which may be significant especially in very low birth weight (VLBW) infants.

Conditions requiring a Neonatologist to be present at the delivery

• Preterm delivery
• Breech delivery
• Cesarean section (C-section)
• Instrumental delivery (forceps or vacuum extraction)
• Multiple Birth
• Intrauterine growth restriction
• Perinatal asphyxia
• Congenital malformation

Apgar score

APGAR score reflects postnatal adaptation from the several aspects (see the Table below) and a newborn is scored in the 1^st, 5^th and 10^th minute of life (each aspect can get a score of 0, 1 or 2 points). Therefore, for a physiologic newborn, the score can be 8-10 in the first minutes of life, while babies with APGAR score of 4-7 tend to suffer from mild to moderate perinatal asphyxia. Last but not least, scores of 0-3 indicate severe perinatal asphyxia.

References

① Gill AW. Postnatal cardiovascular adaptation. Arch Dis Child Fetal Neonatal Ed. 2019;104(2):F220-F224. doi:10.1136/archdischild-2017-314453