The etiology of preterm premature rupture of membranes (PPROM) remains unclear. We hypothesize that tissue remodeling in fetal membranes, specifically the chorion, results in weakening and rupture. We sought to quantify the chorion cell layer in fetal membranes from PPROM, preterm labor (PTL), and term subjects.
A retrospective investigation was performed on clinically collected fetal membrane samples from 75 subjects delivered at Duke Medical Center (25 in each group: PPROM, PTL, and term labor). Paraffin embedded fetal membrane histologic sections were obtained. Immunohistochemistry was performed using a primary antibody against cytokeratin. A Zeiss Axio Imager fluorescence microscope was used to take 2 digital images of each quadrant of fetal membranes on each slide (8 images per slide). ImageJ software was used to measure the chorion and decidua in 4 distinct regions of the image (32 measurements/subject). The average chorion thickness and the % chorion of choriodecidua thickness were calculated and compared among the 3 groups. Statistical analysis was performed by Kruskal Wallis and chi square where appropriate.
There was no difference in maternal age or race between groups. Chorion cell layer thickness in PPROM subjects was significantly smaller when compared to PTL and term subjects (70.8 vs. 92.0 vs. 160.4.4 μm, p<.0001). Also, the % chorion of choriodecidua was significantly less in PPROM compared to PTL and term subjects (15.7 vs. 25.1 vs. 35.7%, p<.0001). For all subgroups analyzed, there appeared to be a dose response effect which was demonstrated least in term subjects and greatest in PPROM subjects. Further, when severe histologic chorioamnionitis was excluded from analysis, the results were similar (76.6 vs. 81.8 vs. 160.4 μm, p=.0006)
Premature destruction of the chorion cell layer of fetal membranes appears to be more common in PPROM compared to PTL and term subjects. Furthermore, when severe chorioamnionitis is excluded, the findings were unchanged, suggesting that this finding may be independent of infection.
© 2008 Mosby, Inc. Published by Elsevier Inc. All rights reserved.