Abstract
The content of the low-molecular weight protein β2-microglobulin and albumin was measured by immunochemical methods in amniotic fluid from 136 patients in the 13th to the 43rd week of pregnancy. Parallel estimations of β2-microglobulin in maternal plasma were made in the majority of patients. Some samples of cord serum and urine from the newborn were also analysed. In normal patients the levels of β2-microglobulin followed the albumin pattern with a peak value around the 24th week and a gradual decrease during the last trimester. In contrast to other proteins β2-microglobulin showed higher levels in amniotic fluid than in maternal plasma. During the last trimester levels in maternal plasma exhibited a significant increase. Levels in cord serum were higher than in amniotic fluid. Urine from the newborns contained at least 5 times the amount previously found in adults. The results indicate that β2-microglobulin in amniotic fluid is largely derived from the fetus itself. Patients with pregnancies complicated by haemolytic disease showed significantly higher levels in amniotic fluid than normal patients for comparable periods but the levels showed no close correlation with the degree of fetal involvement. The ratio of β2-microglobulin to albumin in amniotic fluid was elevated in patients with fetal haemolytic disease. The albumin content showed no significant differences between the clinical groups but tended to decrease more rapidly during the last weeks of pregnancy in patients with fetal haemolytic disease. Further studies of β2-microglobulin might supply important information about the transfer mechanisms of amniotic fluid proteins and also permit studies of some physiological and pathological processes in the fetus.