Decreased adherence and spontaneous separation of fetal membrane layers – amnion and choriodecidua – a possible part of the normal weakening process

A) Determination of Percent Spontaneous FM Separation; B) FM in T-peel adherence testing apparatus – Amnion and choriodecidua being peeled apart between the clamp jaws (1=force sensing load cell, 2=upper clamp pulling amnion vertically upwards, 3=amnion peeling from choriodecidua, 4=horizontal platform of the lower clamp supporting unpeeled FM floating over cold saline, 5=lower clamp holding choriodecidua. (Fig. 1B borrowed from reference 7 with permission); C) FM in T-peel testing apparatus (detail).

Distribution of Percent Spontaneous Separation in 232 FM. The number of FM in which the percentage of separation fell within each percentage decile are shown. Percentage separation was determined by the weight of separated areas divided by the total weight of separated plus adherent areas of each FM as described in Methods.

Effect of Labor upon Spontaneous FM Separation and Adherence: A) FM from vaginal deliveries had significantly more spontaneous FM separation compared to those from unlabored, elective cesarean section (*p=0.046). B) FM from vaginal deliveries had significantly lower average forces of FM layer adherence compared to FM from unlabored, elective cesarean section deliveries (*p=0.005). Abbreviations: SVD, vaginal delivery. Data shown as mean±SEM.

Effect of Mode of Delivery on Spontaneous FM Separation and Adherence: A) Measurements of degree of FM separation demonstrated a clear gradient across modes of delivery: C/S<AROM SVD<SROM SVD. (C/S vs SROM SVD, *p=0.008; AROM SVD vs SROM SVD, *p=0.046). B) Vaginally delivered FM with both SROM and AROM had significantly lower average forces of adherence compared to FM from unlabored, elective C/S deliveries (SROM SVD vs. C/S, p=0.015; AROM SVD vs. C/S, *p=0.02). Abbreviations: C/S, cesarean section; AROM, artificial rupture of membranes; SVD, vaginal delivery; SROM, spontaneous rupture of membranes. Data shown as mean±SEM.

Effect of Gestational Length upon FM Separation and Adherence. A) Effect of gestational age on spontaneous FM separation. Premature FM (<37 weeks) had significantly less spontaneous FM separation compared to term FM (≥37 weeks) for all modes of delivery (p<0.001; premature, n=28; term, n=204). Data shown as mean±SEM. B) Effect of gestational age on average force of FM layer adherence. Adherence of premature FM (<37 weeks) was significantly greater than adherence of term FM (≥37 weeks) for all modes of delivery (p<0.001; premature FM, n=6; term FM, n=24). Data shown as mean±SEM.