Appendix 6. Prematurity - Review of Medical Embryology Book

Introduction: any newborn infant born alive who weighs 2500 g (5.50 lb) or less is considered a premature infant. This would include some infants of apparently full-term gestation
Signs of premature infancy (clinical and x-ray features)

WEIGHT AND LENGTH are less than 2500 g and 47 cm at birth. The gestation period is usually 28 to 36 weeks
THE CRY is more feeble than that of a full-term infant, sucking is weaker, and there is general weakness with sluggish movements
THE SKIN is thin and wrinkled, there are abundance of lanugo and minimal amount of subcutaneous tissue, and the nails are soft
THE HEAD appears large, but the circumference is less than 33 cm, with a characteristic widened face
THE TEMPERATURE is low and unstable
THERE IS A TENDENCY to cyanosis and irregular respirations
JAUNDICE may be prominent and continue longer than in full-term infants
FEEDING DIFFICULTIES are common with vomiting more frequent and a tendency to loose stools
INITIALLY THE WEIGHT LOSS is often greater and weight recovery not rapid, in contrast to a full-term infant
THE DISTAL FEMORAL AND PROXIMAL TIBIAL OSSIFICATION CENTERS may be absent. In the full-term infant, these are present including those of the calcaneus, cuboid, talus, and proximal tibia

A WEAK GAG AND COUGH REFLEX and an immature respiratory center that requires stronger afferent stimuli for response; incompletely developed alveoli; reduced vascularity of the pulmonary capillaries, sparse pulmonary elastic tissue; poor muscle tone and weak movements of the intercostal muscles and diaphragm plus softness and pliability of the bones of the thoracic cage which reduces intrathoracic pressure; and the presence of fetal hemoglobin which releases oxygen less readily to tissues
CYANOSIS OF THE EXTREMITIES and edema; paucity of vascular elastic tissue and low body reserves of vitamin C, resulting in capillary fragility and potential hemorrhage
SUCKING REFLEX is very weak and hepatic immaturity predisposes to the development of increased bilirubinemia with jaundice. The slow rate of secretion of digestive enzymes and gastric acid causes diminished tolerance, resulting in vomiting, diarrhea, and poor absorption of fats and minerals
DECREASED RENAL FUNCTION produces dehydration and acidosis
THE FAULTY CONTROL OF BODY TEMPERATURE is associated with hypothermia and hyperthermia due to inadequate function of the sweating mechanism, decreased body insulation (less fatty tissue), and low total heat production due to body inactivity and poor muscle development
THE POOR STORAGE OF MINERALS, vitamins, and immune materials makes the premature infant subject to rickets, anemia, and a variety of infections

THE SURVIVAL RATE is directly in proportion to the weight of the premature infant at birth, and the prognosis improves as the period of gestation is lengthened
PREMATURITY is one of the leading primary causes of neonatal deaths, and most of these occur in the first 24 hours, fewer in the second 24 hours, and even fewer after that
THE MAJOR CONTRIBUTING FACTORS FOR DEATH include anoxia, intracranial hemorrhage, hyaline membrane with resorption atelectasis, pneumonia and other infections, congenital malformations, and blood dyscrasias