DIFFERENT BIOMECHANICAL PROPERTIES OF HUMAN FETAL MEMBRANES OBTAINED BEFORE AND AFTER DELIVERY

The aim of this study was to elucidate whether the mechanical properti es of fetal membranes change during late pregnancy and labour. Membran es delivered by elective caesarean section in week 38 showed different load-strain curves to membranes obtained after spontaneous vaginal de livery at term. A major change in mechanical properties was a decrease in strength of the intact chorioamniotic membrane from 1.39 N to 0.98 N (width of biopsy 4 mm), mainly due to loss of strength of the amnio tic component, from 1.27 N to 0.72 N. Moreover, the extensibility of t he chorionic component ((epsilon)F(max)) increased after vaginal deliv ery from 0.42 to 0.54, resulting in a two-component behaviour of the i ntact chorioamniotic membrane and further decrease of strength. Based on these observations it is suggested that the amnion is attached to t he chorion, act biomechanically in parallel and possess relatively hig h mechanical strength during pregnancy. After vaginal delivery the two membranes are separated, and pronounced changes are induced in their mechanical properties.