Myoglobin in third trimester amniotic fluid of human pregnancy--a potential indicator of fetal hypoxia.

195 amniotic fluid samples from the third trimester were examined for their content of myoglobin by means of radio-immunoassay. 151 of the samples were obtained intrapartum, the rest (44) was taken antepartum by transabdominal amniocentesis within one week prior to delivery. Depending on the myoglobin levels measured, different amniotic fluid groups were defined: (A) amniotic fluids containing no myoglobin or traces of it (less than 3 ng/ml), (B) amniotic fluids with moderately elevated myoglobin levels (3-10 ng/ml), (C) amniotic fluids with high myoglobin levels (greater than 10 ng/ml). Myoglobin levels above 3 ng/ml could be measured in 98 of the 151 samples taken intrapartum. In the amniotic fluids drawn antepartum the proportion of "myoglobin-positive" samples (greater than 3 ng/ml) amounted to only 22.7% (10 out of 44 samples). In pregnancies with amniotic fluids showing high myoglobin levels intrapartum, the prevalence of meconium staining of the samples, pathological cardiotocograms intrapartum and metabolic acidoses in umbilical artery blood samples was significantly higher than in pregnancies with myoglobin-negative amniotic fluids. The frequency of cesarean sections for fetal distress rose with increasing myoglobin levels in amniotic fluid, being 5.7, 13, and 18.2% in Group A, B and C respectively. In the pregnancies in which the amniotic fluid samples were taken antepartum, the prevalence of meconium-stained amniotic fluid increased with elevating amniotic fluid myoglobin (p less than 0.05, Group A vs. Group C). The frequency of cesarean sections for fetal distress and of neonatal depression immediately after delivery was considerably heightened in the cases with myoglobin-positive amniotic fluids antepartum compared to those with myoglobin-negative liquor.(ABSTRACT TRUNCATED AT 250 WORDS)