To answer your question, I'm going to insert the relevant excerpt from the mini-reviews section of the VBAC chapter in the forthcoming new edition of my first book, Obstetric Myths Versus Research Realities. (The new edition will be co-authored by Amy Romano and published by University of Michigan Press.) I took the lead on the VBAC chapter, and one of my goals was to quantify risks wherever I could. Questions such as yours validate the many hours I spent poring over studies and compiling data.
-- Henci
Single-layer uterine suturing: 0-3.1% range in scar rupture rate (Bujold 2002; Chapman 1997; Tucker 1993) The largest study reported a rate of 3.1% with single-layer closure (15/489) versus 0.5% with double-layer suturing (8/1491) (Bujold 2002). Single-layer closure remained a factor after accounting for confounding variables. Two smaller studies of 70 and 149 single-layer closures versus 75 and 143 double-layer closures reported no scar ruptures with either type (Chapman 1997; Tucker 1993). We have omitted another small study from the range because its results were so far out of line with other studies. It reported an extremely high rate of scar rupture with single layer closure: 8.6% (3/35) versus 1.3% (12/913) with double-layer. Investigators thought this might be attributable to inducing with misoprostol (Gyamfi 2006). The results of Locatelli et al. (2004) strongly suggest that management factors affect scar rupture rates. Despite half the women having single-layer closure, the scar rupture rate even with labor induction was only 0.3%. (For more details on induction and augmentation protocol, see “Inducing labor is associated . . .” and “Augmenting labor may increase . . . .”) Another factor confounding evaluation of the effect of single-layer uterine suturing is differences among studies in suture material and technique. Unfortunately, we have no data about which suture techniques and materials produce the strongest scar.
Bujold E, Hammoud A, Schild C, et al. The role of maternal body mass index in outcomes of vaginal births after cesarean. Am J Obstet Gynecol 2005;193(4):1517-21.
Chapman SJ, Owen J, Hauth JC. One- versus two-layer closure of a low transverse cesarean: the next pregnancy Obstet Gynecol 1997;89(1):16-8.
Gyamfi C, Juhasz G, Gyamfi P, et al. Single- versus double-layer uterine incision closure and uterine rupture. J Matern Fetal Neonatal Med 2006;19(10):639-43.
Locatelli A, Regalia AL, Ghidini A, et al. Risks of induction of labour in women with a uterine scar from previous low transverse caesarean section. BJOG 2004;111(12):1394-9.
Tucker JM, Hauth JC, Hodgkins P, et al. Trial of labor after a one- or two-layer closure of a low transverse uterine incision Am J Obstet Gynecol 1993;168(2):545-6.