Amniotic fluid biochemistry in second-trimester trisomic pregnancies: relationships to fetal organ maturation and...

Protein and enzyme patterns were investigated in amniotic fluid samples of 12 trisomy 21 and five trisomy 18, between 11 and 16 weeks and of a control group of 50 chromosomally and anatomically normal pregnancies at the same gestational age. Positive correlations were found between gestational age and the concentration of urea (P<0.05), creatinine (P<0.01), beta2-microglobulin (P < 0.0001), hCG (P < 0.01), ALP (P < 0.001), LAP (P < 0.0001) and GGT (P <0.0005) in the amniotic fluid of euploid pregnancies. There were also significant correlations between the concentrations of the different variables measured except for hCG and AFP. Different protein and enzyme patterns were found in the amniotic fluid of aneuploid pregnancies where only beta2-microglobulin concentration was significantly correlated with advancing gestational age. The beta2-microglobulin concentration was significantly (P <0.05) higher in aneuploid fetuses presenting with hydrops compared to those without. These findings suggest that the changes in amniotic composition found during the fourth month of normal pregnancies reflect mainly the maturation of the fetal renal glomerular function and the arrival of enzymes from the digestive and respiratory tract into the amniotic cavity. In trisomy 21, there is evidence of a delay in the maturation of these organs whereas in trisomy 18, there is a reduced production of most proteins and enzymes.