Objective: The proteoglycan decorin stabilizes collagen whereas biglycan and hyaluronan disrupt well-organized collagen. The aim was to compare hyaluronan and proteoglycans in human fetal membranes obtained before and after spontaneous labour at term.
Study design: Prelabour samples of fetal membranes (N=9) were obtained from elective caesarean sections and regionally sampled from over the cervix (cervical membranes) and mid-zone samples between this area and the placental edge. Postlabour samples (N=11) were obtained from spontaneous vaginal delivery and also regionally sampled. Amnion and chorio-decidua were analysed separately. The proteoglycans decorin and biglycan were analysed using alcian blue precipitation, SDS polyacrylamide gel electrophoresis and immunostaining. Hyaluronan was analysed using a radioimmunoassay and by histochemistry. Collagen was measured by estimating hydroxyproline content.
Results: In prelabour membranes the biglycan concentration (microg/mg wtw) in the cervical amnion was 40% lower than in the mid-zone amnion (P<0.05). After delivery the cervical amnion showed a twofold increase in biglycan (P<0.05), a 30% decrease in collagen (P<0.05), and a 50% decrease in decorin concentration (P<0.05). In mid-zone samples after delivery the concentrations of hyaluronan showed an increase form 1.0 to 4.9 microg/mg wtw (P<0.05). Histology demonstrated a gelatinous substance, which separated amnion and chorio-decidua, in particular at the cervical site. This gelatinous substance contained hyaluronan at a concentration of 3.0 microg/mg wtw.
Conclusion: It is well established that prelabour fetal membranes are considerably stronger than postlabour fetal membranes. Two features may explain this; a weakening of the amnion combined with a separation of amnion and chorio-decidua. The biomechanical changes are consistent with the decrease in collagen and decorin, and the increase in hyaluronan and biglycan demonstrated in this study. The separation of the membranes is caused by the formation of a gelatinous substance, rich in hyaluronan. The results indicate that the biomechanical changes are not merely secondary to the stress of labour but that an active maturation process is involved.