Urinary trypsin inhibitor levels in amniotic fluid of normal human pregnancy: decreased levels observed at parturition.

Abstract Objective: Urinary trypsin inhibitor, a light chain of inter-α-trypsin inhibitor, is reported to inhibit uterine contractility during pregnancy. The objective was to measure amniotic fluid urinary trypsin inhibitor levels in women throughout pregnancy. Study Design: We determined levels of urinary trypsin inhibitor in human amniotic fluid (n = 40) by means of Western blot analysis. For quantification, computerized scanning and densitometry were used. Results were analyzed for statistical significance with the Mann-Whitney U test. Results: During pregnancy, mean amniotic fluid urinary trypsin inhibitor levels (±SD) were 1.5 ± 0.22, 1.2 ± 0.18, and 0.58 ± 0.24 μmol/L at 15 to 22 (n = 10), 30 to 35 (n = 5), and 37 to 40 (n = 10) weeks' gestation, respectively. There was a significant negative correlation of urinary trypsin inhibitor level with gestational age. A significant difference was observed in amniotic fluid urinary trypsin inhibitor levels before and after (0.10 ± 0.03 μmol/L; n=15) the onset of labor. Conclusion: Amniotic fluid urinary trypsin inhibitor levels decrease significantly at term. These results support the hypothesis that parturition may occur through the down-regulation of urinary trypsin inhibitor, which may decrease uterine contractility and maintain the uterus in a state of quiescence during pregnancy.(Am J Obstet Gynecol 1999;180:141-7.)