The low hydroxyproline content of prematurely ruptured human fetal membranes

Since collagen is one of the main factors responsible for the mechanical properties of soft tissue, we have determined the hydroxyproline content of the placental amnion, the free amnion and the chorion of 32 unruptured and 25 prematurely ruptured human fetal membranes. The hydroxyproline content of prematurely ruptured membranes was approximately 50% lower than in unruptured membranes. Hydroxyproline (microgram/mg lyophilized tissue), reported as mean +/- SD, was: 19.46 +/- 3.60 vs 37.53 +/- 8.93 for placental amnion; 16.97 +/- 3.93 vs 33.00 +/- 8.25 for free amnion, and 7.74 +/- 3.00 vs 13.23 +/- 3.95 for the chorion. This finding and the known decrease of hydroxyproline content of the amnion towards the end of gestation in normally evolving pregnancies suggest that an abnormally low collagen content may be the general cause of prematurely ruptured human fetal membranes.