Chorioamniontis in preterm delivery is associated with degradation of decorin and biglycan and depletion of hyaluronan in fetal membranes.

OBJECTIVE: The proteoglycan decorin stabilizes collagen whereas biglycan and hyaluronan disrupt well-organized collagen. The aim was to determine the concentrations of these constituents in fetal membranes in relation to gestational age, preterm labour, PPROM and chorioamnionitis.

STUDY DESIGN: Preterm fetal membranes (24-34 weeks gestation) were obtained from elective caesarean deliveries (N = 4), from PPROM (N = 14), and from preterm labour (N = 14). Term fetal membranes from elective caesarean deliveries (N = 9) and spontaneous vaginal deliveries (N = 11) were used for comparison. Chorioamnionitis was assessed histologically. The proteoglycans were analysed using alcian blue precipitation, SDS-PAGE and immunostaining. Hyaluronan was estimated by a radioimmunoassay.

RESULTS: Preterm amniotic membranes with chorioamnionitis displayed a 8-fold decrease in hyaluronan concentration as well as a pronounced (88%) degradation of decorin and biglycan (p < 0.05). The amnion from preterm elective caesarean sections had higher decorin (3.2 vs. 1.7 μg/mg, p < 0.05) and lower biglycan (0.4 vs. 1.0 μg/mg, p < 0.05) concentrations as compared to similar term amnion (p < 0.05), whereas the hyaluronan concentrations were not associated with gestational age. Also the chorio-decidua from preterm caesarean sections had higher decorin concentrations (1.8 vs. 1.0 μg/mg, p < 0.05) whereas the biglycan concentration was unchanged. Labour (term as well as preterm) was characterized by increased hyaluronan and biglycan concentrations in the amnion (not statistically significant).

CONCLUSION: The biglycan/decorin balance increases during third trimester of pregnancy and during active labour. This relation might contribute to mechanical weakening of the membranes. Chorioamnionitis induces dramatic degradation of both proteoglycans and hyaluronan, which can explain the decreased biomechanical strength.