We are very interested with the point-of-view of Ahn et al regarding our results. In summary, they suggest that the main factor that negatively influences the residual myometrial thickness (RMT) is not necessarily the inclusion of the decidua in the suture but possibly the uncoaptated portion of the myometrium (described as X-A 0 ) that is the consequence of uterus’ dynamism and contractions. Their hypothesis supports the observation that a double-layer could lead to better healing than a single-layer by reducing the uncoaptated portion of the myometrium.
We believe that optimization of the myometrium-myometrium coaptation is probably the key to reach better healing of uterine scar and minimizing decidual inclusion (the D 0 -D 1 line), as suggested by Anh et al, is 1 way to reach that goal. It is possible that the specific coaptation of the decidua-decidua (B-D 0 with B’-D 0 ’) layers could also improve the RMT. Poidevin observed that the exclusion of the decidua was associated with a lower risk of scar defect; Hayakawa et al, who used a different technique of uterus closure and uterine scar evaluation, observed the opposite: the specific coaptation of the decidua (inclusion) was associated with low risk of scar defect. Therefore, it remains unclear whether the first-layer should be limited to a small portion of the myometrium over the decidua (excluding it) or to the decidua itself (including it); however, from our surgical experience, the difference is probably more theoretic than clinically relevant, because the goal is to achieve an optimal approximation of the similar tissues.
A randomized trial that would evaluate the impact (beneficial, detrimental, or no effect) of decidual inclusion specifically would be difficult to perform because of the importance of minimizing the size of the inclusion (the D 0 -D 1 line) to optimize the benefits on RMT as suggested by Ahn et al. Most surgeons do not consider that parameter in their uterus closure, and it could be difficult to control for this specific factor of uterine scar healing. However, we agree with the authors that a randomized trial would compare (1) a full inclusion of the decidua with a large portion of myometrium (a wide D 0 -D 1 line) for the first-layer, which is still used in some North American centers, with (2) a uterus closure that limits the first-layer to a small portion of the myometrium right above the decidua (or minimally including it) to reduce decidual inclusion into the scar could be beneficial for the obstetrics community. Such a trial should include not only long-term follow up to the next pregnancy to estimate the effect of uterus closure on uterine scar and uterine rupture but also placental defects. Sumigama et al reported that including the inner side of the uterine wall (decidua/endometrium) into the scar with a continuous suture was associated with an increasing rate of placenta accreta in women with placenta previa, independently of the number of layers used for uterus closure.
In conclusion, in regards with the best evidence available and for the best interest of women and child health, we believe that the next steps should focus on the development of tools to optimize knowledge transfer from bench to bedside with the following aims: (1) to reduce the use of locked single-layer closure of the uterus including the decidua in nonurgent caesarean delivery and (2) to implement the use of uterine scar evaluation during pregnancy with ultrasound throughout all communities. Measurement of the low-uterine segment thickness in the third trimester is probably the best ultrasonographic marker to estimate the risk of uterine scar defect. Its use in clinical practice has been associated with a low risk of uterine rupture during a trial of labor in women with previous low-transverse cesarean delivery.