Human amniotic and fetal neonatal pharyngeal fluids

Testing for fetal lung maturation: a biochemical "window" to the developing fetus

Fetal lung maturity testing represents a major milestone in perinatology. This article critically evaluates specific controversies regarding the methodologies used to measure pulmonary surfactant in AF and how well each of these techniques performs both in principle and application. The clinical utility of fetal lung maturity testing as it applies to particularly difficult complications of pregnancy is discussed. These technical and clinical issues are framed by the scientific and empiric evidence that is used as the rationale for such testing and its implementation in the effective management of preterm delivery.

Pulmonary surfactant: hydrophobic nature of the mucosal surface of the human amnion

The contact angle has been measured for a drop of saline placed upon the rinsed mucosal surface of the amnion in eleven human placental membranes obtained from normal births at full term. The contact angle averaged 70 degrees, indicating a hydrophobic surface comparable with graphite (86 degrees), polyethylene (94 degrees) or oxyntic tissue (85 degrees) which is also exposed to endogenous surface-active phospholipids in vivo. By comparison, four pre-term placentas with an average gestation period of 29.5 weeks gave a mean contact angle of 32 degrees, indicating that hydrophobicity of the placenta increases with maturity (41 weeks) and might well be imparted by adsorbed surfactants present in amniotic fluid and known to render other surfaces hydrophobic. Since the mucosal epithelium of the amnion is exposed to the same surfactants in the same physical state as the fetal alveolar wall, the above results imply that this surface may also be hydrophobic, as indicated in the adult lung by other studies. The concept of surfactant directly adsorbed to the pulmonary tissue surfaces is discussed in connexion with its possible functional advantages in 'de-watering' the lung at birth, maintaining homeostasis by water repellency , releasing airway surfaces and lymph ducts glued by protein and lubricating tissue respiratory movement.

Methods of evaluating fetal lung maturity

Respiratory distress syndrome occurs in infants born with immature lungs. The immature fetal lung lacks an adequate supply of surfactant, a phospholipid-rich substance which is produced in the type II cells of the alveolar epithelium. In the fetus, surfactant is secreted into the potential air spaces of the lung and passes into the amniotic fluid as gestation proceeds. It is now clear that most methods currently in use for assessing fetal lung maturity depend on the detection of a sudden release of surfactant into the amniotic fluid as the lung reaches a critical stage of maturity. These methods, which include the lecithin/sphingomyelin ratio, the lung profile, total phospholipid or lecithin concentration, fluorescence depolarization, lamellar body phospholipid concentration, and the "shake" test, are reviewed in the light of recent understanding of the nature of surfactant. In assessing each method, we have examined possible sources of error in performing the test in the laboratory, factors which could theoretically limit its ability to reflect the state of fetal lung maturity and current information regarding its reliability, in terms of clinical performance. Guidelines for future research in this area are also suggested.

Fetal respiration. A review

During recent years respiratory movements by the human fetus have been rediscovered. The types of movements have been defined, and their dependence on some physiologic conditions has been described. Pharmacologic agents influence not only the occurrence of the movements but also their rate and depth. A tidal flow of fluid between lung and amnionic sac has been established, which may play an important role in lung development. Demonstration of this route for exchange of water and soluble substances identifies the lung as an organ very likely involved in exchange between fetal compartments. Additionally, the deposition in the lung of the particulate matter contained in amnionic fluid may not be proof of pathologic aspiration as previously thought.

Phosphatidylcholine content and fatty acid composition of tracheal and gastric liquids from premature and full-term newborn infants

The phosphatidylcholine content and fatty acid composition of tracheal and gastric liquids from newborn full-term and premature (30-36 weeks) infants were studied. Phosphatidylcholine accounted for about 70% of the total phospholipids in both liquids from the full-term infants but only 55-57% of those from the prematures. There was a significant correlation between tracheal and gastric liquids in the fatty acid composition of phosphatidylcholine. There were significant differences in fatty acid composition between the full-term and premature liquids. These differenences were most apparent in the gastric liquid. It is suggested that phospholipid or fatty acid analysis of tracheal or gastric liquids from newborn infants can be used in the assessment of pulmonary maturity.

The origin of amnitoic fluid lecithin

Lecithin has been measured in amniotic fluid, pharyngeal aspirate, fetal and maternal plasma and fetal membranes from the same pregnancy. In the amniotic fluid from a term pregnancy 79 per cent of the lecithin is found in the reconstituted precipitate of centrifuged fluid. It is suggested that the lecithin of amniotic fluid may originate from sources other than fetal lung and that lecithin concentration is therefore a measure of overall fetal maturity.