Antenatal Corticosteroids at the Beginning of the 21st Century

Abstract

Corticosteroids administered to women in preterm labor are the standard of care for reducing neonatal morbidity and mortality associated with prematurity. These agents promote lung development and reduce the incidence of neonatal intraventricular hemorrhage. Several studies have investigated the method by which fetal lung fluid is cleared after birth. This exploration resulted in the elucidation of the Starling equation or the hypothesis that fluid filtration through capillary membranes is dependent on the balance between the pressure blood places on the capillary membranes and the osmotic pressure of the membranes. The clinical observation that a neonate experiences a vaginal squeeze during a vaginal birth may be important, but it can account for only a small percentage of the lung fluid absorbed. Perhaps more importantly, amiloride-sensitive sodium transport channels (ENaCs) have emerged as key factors in the movement of alveolar fluid from the lung into the vascular system. Several potential clinical applications have been developed from this new knowledge about the physiology of lung fluid clearance at birth. Neonates born late preterm or at term by elective cesarean before the onset of labor are more likely to develop respiratory distress than those born vaginally. Based on the mechanism of action of antenatal corticosteroids, these drugs may be beneficial in the clearance of fetal lung fluid in this population. This article reviews how fetal lung fluid is cleared; the pharmacologic effects of corticosteroids on the fetus; and the risks, benefits, and controversies associated with corticosteroid use.

Measuring Physiological Changes during the Transition to Life after Birth

“…Lung liquid clearance by ‘vaginal squeeze' is an old theory some authors still consider as an important mechanism [22]. This theory originates from studies [5,23] performed in 1917 and repeated in 1962 using X-ray imaging showing compression of the fetal chest of term infants passing through the birth canal.…”

“…In contrast, as postural changes during labor can cause lung liquid loss [29], flexion of the fetal trunk, which increases abdominal pressure and elevates the diaphragm, are more likely to cause liquid expulsion [22,23]. …”

The first breaths of life: imaging studies of the human infant during neonatal transition

“…However, the little resistance that the chest offers when it follows the head through the birth canal makes it unlikely that 'vaginal squeeze' significantly influences liquid clearance [14,15]. Postural changes during labor can cause lung liquid loss [16] and flexion of the fetal trunk during delivery, which causes an increase of abdominal pressure and elevation of the diaphragm, are more likely to cause liquid expulsion [11,13].…”

“…Currently, there is still a common belief among caregivers that the vaginal squeeze is important for lung recruitment [13]. However, the little resistance that the chest offers when it follows the head through the birth canal makes it unlikely that 'vaginal squeeze' significantly influences liquid clearance [14,15].…”

Molecular and Physiological Determinants of Pulmonary Developmental Biology: a Review

“…Loss or insuffiency of HIF-2α culminate in impaired pulmonary development, decreased surfactant production, ARDS and even neonatal death [103]. Prenatal and post natal exposure to glucocorticoids (betamethasone, dexamethasone and cortisol) have been demonstrated by various studies, to be helpful for epithelial cell maturation and improved amounts of pulmonary surfactant and suppressed inflammatory response [104,105,106,107]. Other elements that retard IUG include Chest wall anomalies, diaphragmatic hernia, Oligohydroamnios, Rhesus Isoimmunization, Renal anomalies, Myotonic Dystrophy, Anecephaly, Maternal diabetes, Alcohol and Nicotine, while sex hormones and several growth factors discussed in molecular mechanisms of lung growth are also known to affect fetal and neonatal lung development [23].…”