584: Human uterine contractility at term in relation to previous cesarean section

Abstract

The efficiency of myometrial contractility in labor, for the woman who have had a previous cesarean delivery (CD), is an important factor for women undergoing trial of labor after a cesarean. There are no data, to our knowledge, on this topic. The aim of this study was to examine a range of contractile parameters in human myometrial tissue in vitro, and compare the results obtained between the following 3 groups: Women with no previous CD (CD=0); Women with 1 previous CD (CD=1); Women with greater than one CD (CD=>1). Myometrial biopsies were obtained at CD, performed at term, from n=74 women, with Institutional Ethical Review Board approval, Galway University Hospital. Myometrial strips were dissected into 8 uniform samples, and suspended for in vitro tissue bath analysis under physiological conditions, as previously described [1]. The following parameters of contractile performance for spontaneous contractions were measured: maximal amplitude (MAMP), mean contractile force (MCF), time to maximal amplitude, maximum rate of rise, frequency and occurrence of simple and complex (biphasic and multiphasic) contractions. Comparisons were made across the 3 groups as follows: CD=0 n=22; CD=1 n=37; CD=>1 n=15. Statistical analysis was performed using T-Test Assuming Unequal Variance. The results obtained for the different contractile parameters, for the 3 groups, are shown in Table 1. 592 tissue samples were analysed from 74 women. The only significant difference (Table 2) in contractile parameters found was in the frequency of contractions, with a lower frequency of contractions in the CD=1 group compared to CD=0 and CD=>1 groups (p=6.36E-06 and p=0.000135 respectively). These data indicate that there is no significant difference in the general biological characteristics of human uterine contractions in vitro, in women who have had one, or greater that one previous CD, in comparison to women who have had none. The only notable feature is that the frequency of contractions was greater in the sub-group of women who had one previous CD. These findings indicate that factors other than the functional contractility of uterine tissue, may be responsible for the increased CD rate observed among women undergoing VBAC.