Factors influencing success in the fetal-neonatal transition in dogs.

Fetal-neonatal transition is a physiological process requiring numerous neonatal organic and autonomous adaptations, such as onset of pulmonary respiration, clearance of airway fluid, and adequate ventilation of airspaces, in addition to activation of thermoregulatory mechanisms and cardio-vascular changes. When a newborn does not fully and rapidly perform its adaptive functions due to negative factors, the chances of neonatal morbidity and mortality increase significantly. Factors that can influence the success of the fetal-neonatal transition are, but not restricted to: placental morphology and functionality, meconium-stained amniotic fluid, litter and neonatal features, and the delivery conditions. Placental vascular morphofunctionality related to erythrocyte clusters, hemosiderin granules and overall iron metabolism in marginal hematomas influence neonatal vitality. When fetuses release meconium into the amniotic fluid, there is neonatal hypoxia exacerbation, low efficiency in tissue oxygenation and thermoregulatory challenges. The birth weight and sex of the neonates are related to pulmonary maturity at birth, directly influencing respiratory efficiency of heavier and female puppies. Regarding obstetric conditions, c-section neonates experience delays in pulmonary clearance, respiratory adaptation, and reflex responses, while vaginal-born neonates are subjected to higher oxidative stress. However, in c-section of large litters, the last puppies delivered have higher systemic protein oxidation compared to the first one or those born via vaginal delivery, indicating that oxidative challenge increases with longer surgical times. In conclusion, successful fetal-neonatal transition depends on characteristics prior to birth, as well as the influence of factors during labor (obstetric conditions), individual or litter factors, among other maternal factors that warrant further investigation.