FROM GESTATION TO NEONATAL LIFE IN THE CANINE SPECIES: MATERNAL AND FETAL PHYSIOLOGY AS PREDICTORS OF PERINATAL OUTCOME

Abstract

The objective of this work is to deepen and generate an integrated vision of the physiological and pathological aspects that may appear during the gestation of, childbirth or neonatal adoption, with special emphasis on the determination of risk factors through the use of biomarkers, which allow clinical decisions to be made. Progesterone is primarily responsible for maintaining gestation, which is secreted by the corpus luteums. The sudden drop in the hair is one of the first indicators that labor is beginning. However, other hormones with estrogen do not appear to play a major role during this process. Recent studies support the theory that fetal maturation and increased fetal cortisol may play a key role in the onset of labor. In addition, prolactin has been determined to be an important luteotropic hormone in maintaining progesterone levels. Birth planning is very important, especially in those pregnancies where there is a high risk of dystocia, as well as in case you want to schedule a cesarean section. That is why different parameters are used, such as: plasma progesterone levels, heart rate monitoring, control of other measurements such as biparietal diameter, gastrointestinal motility or echogenicity of the kidneys. The neonatal period is defined as the first three to four weeks of the animal's life, which represent a critical stage. During this time, neonates require rapid adaptation in terms of thermoregulation, respiratory and metabolic functions, and immunity. These adaptations require maternal care, colostrum intake, optimal temperature control and adequate environmental hygiene. The most common causes of neonatal morbidity and mortality include hypothermia, hypoglycemia, hypoxia, dehydration, aspiration pneumonia, congenital malformations, and sepsis. Hypoglycemia is particularly frequent in low birth weight puppies due to limited glycogen reserves and immature hepatic gluconeogenesis. Blood glucose levels below 50 mg/dL are associated with neurological depression, seizures, and death. Similarly, hypothermia can impair metabolic enzyme function, reduce gastrointestinal motility, and exacerbate hypoglycemia and immune suppression. Neonates are highly vulnerable to heat loss due to their high surface area-to-volume ratio and lack of brown adipose tissue. Perinatal hypoxia can be affected by prolonged labour or even the use of anaesthetic agents during a caesarean section, which can increase the likelihood of neonatal death. This hypoxia in turn favors the appearance of acidosis, bradycardia, multi-organ alterations... During the delivery process or in caesarean sections, aspiration of meconium may occur, which causes aspiration pneumonia, which can in turn promote respiratory distress and an increase in neonatal mortality due to unknown cause. Congenital malformations such as hydrocephalus, anasarca or skeletal malformations can also contribute to neonatal losses. Many of these causes are usually racially biased. That is why the objective is to determine quantifiable biomarkers that allow neonatal viability to be assessed, such as: blood glucose, lactate, pH or cortisol levels. It has now been observed that high lactate values are related to anaerobic metabolism and poorer perfusion; while pH values below 7.1 suggest metabolic acidosis with a poor prognosis. On the other hand, high levels of cortisol in the amniotic fluid or in the neonatal serum reflect intrauterine stress that is also correlated with low Apgar scores. Therefore, this review tries to bring together the most relevant literature, as well as different clinical strategies in canine reproduction and neonatology, emphasizing early detection, preventive care or intervention based on objective evidence. That is why a set of parameters such as hormonal measurements, fetal monitoring, use of neonatal care tools or the use of biomarkers are used, with the aim of reducing neonatal mortality and improvising the health of mothers and newborns.