Pregnancy

Term Human Fetal Membranes Have a Weak Zone Overlying the Lower Uterine Pole and Cervix Before Onset of Labor

Abstract
The etiology of fetal membrane (FM) rupture is unknown. A hypothesis that FM weaken by a process of collagen remodeling and apoptosis to facilitate rupture has been proposed. Human FM reportedly exhibit a zone of altered histology, postulated to be the FM rupture site, but concomitant FM weakness has not been demonstrated. We hypothesized that a discrete zone of FM with marked weakness, histological change, and evidence of remodeling and apoptosis, develops in late gestation in the FM overlying the cervix. FM from women undergoing pre-labor cesarean delivery were perioperatively marked to identify the FM overlying the cervix, cut with a procedure which facilitates remapping the rupture strength of FM pieces to their former location and orientation on a three-dimensional model, and strength tested. A 10cm FM zone centered at the cervical mark was compared to the remaining FM. Mean rupture strength within the cervical zone was 55% of the remaining FM. The cervical zone also exhibited increased MMP-9 protein, decreased TIMP-3 protein, and increased PARP cleavage coincident with the previously reported zone of altered histology. A discrete zone of weakness is present in term pre-labor FM overlying the cervix that has biochemical characteristics consistent with tissue remodeling and apoptosis.

Key words: Apoptosis • Parturition • Placenta

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