Identification of the pigment in amniotic fluid of erythroblastosis as bilirubin

Amniotic epithelium in rhesus incompatibility: light and electron microscopic examination

Human amniotic epithelium from patients with normal pregnancy (normal amniotic epithelium) and from patients with materno-fetal rhesus incompatibility has been examined under the light and electron microscope. In comparison with normal amniotic epithelium, the epithelium in rhesus incompatibility displays the following morphological changes: 1. Unequal distribution and variable shape of the plump microvilli 2. Considerable narrowing of the intercellular spaces 3. Vacuolization of the cytoplasm 4. Absence of glycogen granules 5. Thickening of the basal membrane. There is a direct correlation between the morphological changes in the amniotic epithelium and the severity of the disease. Since rhesus factors are present only in erythrocytes, it is probably that these changes are not based on a direct immune conflict. On the contrary, they are more likely due to fetal hypoxia and to the cytotoxic effect of unbound, unconjugated bilirubin in the amniotic fluid.

Kinetics of bilirubin photodegradation with application to amniotic fluid

By spectrophotometric methods we have studied the photodegradation of bilirubin in simple solution and in amniotic fluid and have found that: (1) the photodegradation process can be described by kinetics which are first-order in concentration and second-order in time; (2) the photodegradation products of bilirubin do not prevent the determination of the absorbance of the parent compound; (3) although the rate of the photodegradation process depends upon both the oxygen partial pressure and the irradiation intensity, the determination of the original bilirubin absorbance is independent of both of these parameters so long as they are constant over the period of photodegradation; (4) other chromagens in amniotic fluid (including hemoglobin and methemoglobin) experience little photodegradation in the time required to degrade bilirubin; (5) several absorbance measurements over a short (approximately five-minute) period of photodegradation are sufficient for the determination of the original bilirubin absorbance for the complete range of interest in amniotic fluid with an accuracy of about five percent.