POST-MATURITY
Babies born after 42 completed weeks of gestation are termed post-mature, post-term or post-dated babies.
Generally, beyond the term-gestation, placenta cannot sustain adequate fetal growth and develops degenerative changes, leading to fetal hypoxia, distress, growth retardation and sometimes, death.
Etiology: Most cases are idiopathic and born to Primiparous mothers. Rare causes include fetal anencephaly (delayed labor induction) or chromosomal defects, e.g. Seckel's syndrome.
Clinically signs of post-maturity include:
• Long, thin and wasted appearance with low birth weight, due to fetal dysplasia.
• Lack of vernix caseosa with peeling of skin, long nails and deep sole creases at birth.
• Yellowish staining of skin, nails and umbilical cord, due to in utero passage of meconium.
• Complications, e.g. meconium aspiration syndrome, birth asphyxia are common.
Management of these babies includes close monitoring for fetal distress, management of birth asphyxia and meconium aspiration syndrome, and prevention of hypoglycemia by early feeding. Application of oil on skin prevents it from peeling and dryness.
Temperature regulation is the one of the most important aspect of neonatal care, even in normal newborns. Fetus, who enjoys an isothermic environment (37°C) in utero, is suddenly exposed to low environmental temperature at birth, leading to rapid drop in body temperature (~ 0.3°C/min) by all modes of heat loss: (a) evaporation of amniotic fluid, (b) convection due to wind movements, (c) radiation due to temperature gradient, and (d) conduction to substances in contact with skin, e.g. linens.
Normal thermoregulation: Sudden cooling of neonatal skin stimulates cutaneous thermoreceptors, which convey the information to heat regulation centers in pre-optic anterior hypothalamus. Efferents from these centers are mainly sympathetic (adrenergic) in nature and stimulate various mechanisms for heat conservation and production, as follows:
• Heat conservation by peripheral vasoconstriction;
• Heat production by increased muscular activity, e.g.
crying, limb movements, etc. Shivering mechanisms are not mature in newborns.• Heat production by metabolic thermogenesis.
Metabolic thermogenesis is the predominant mode of heat production in newborns, which involves oxidation of metabolic fuels (brown fat) in presence of glucose and oxygen. Brown fat is a highly active metabolic substrate due to large number of mitochondria, predominantly present at the nape of neck, interscapular region, axilla, groin, and around kidneys and adrenals. In a FT-AGA baby, brown fat accounts for ~4% of body weight. Since most of it accumulates in last trimester, preterms have much lesser brown fat, and hence, more susceptible for hypothermia.
Thermoneutral environment: Human body can maintain its temperature only within a limited range, beyond which hypothermia or pyrexia results. However, maintenance of temperature even within this range requires constant metabolic activity, either to generate the heat or to increase evaporative heat loss, e.g. sweating.
Thermoneutral environment is the narrow range of temperature at which baby can maintain its temperature with minimum metabolic activity and oxygen requirements. It varies according to gestation, birth weight and postnatal age, ranging from ~33-31°C in full terms to ~35-33°C in VLBWs (higher value of the range is for first day of life and lower value is for 4th day onwards).
WHO recommends that neonatal temperature should be recorded in axilla once a day in apparently healthy term babies, thrice a day in healthy LBW (2-2.5 kg), 6-hourly in healthy VLBW lt;2 kg and every 2 hourly in sick newborns, using digital thermometer (mercury thermometers have been phased out). Low-reading rectal thermometer must be avoided due to risk of injury but may be used in sick, hypothermic babies with due care, gently inserted ~3 cm (2 cm in preterms) after greasing.
Rectal temperature represents body-core temperature, ~0.5-1.0°C higher than surface temperature.
Clinically too, temperature may be roughly assessed by touching the baby by the dorsum of hand on abdomen and hand/feet. Normal both abdomen and limbs should be warm. Warm abdomen and cold limbs indicate quot;cold stressquot; and cold abdomen and feet indicate quot;Hypothermiaquot;.
Spectrum of temperature in newborns spans from severe hypothermia (lt;32°C) to moderate hypothermia (32-35.9°C), cold stress (36-36.4°C), normal temperature (36.4-37.4°C), fever or hyperthermia (37.5-38.5°C) and hyperpyrexia (gt;38.5°C).
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