It was the first time to find that labor characteristics, intrapartum interventions and perinatal outcomes in VBAC women with cervix dilation strongly resembled those in VBAC women without cervix dilation before the previous cesarean section, but differed significantly from those of multiparae and primiparae.
The Durations Of Labor
We observed that women who underwent VBAC had shorter first and total stage of labor than primiparous women, but were comparable to the multiparous women. Likewise, Zdenek Rusavy et al. showed women with VBAC had a shorter first stage of labor than primiparous women . However, Grylka-Baeschlin et al. demonstrated that overall and first-stage labor duration in women with VBAC were comparable to that of primiparae but significantly longer than that in multiparae . The conflicting results may be due to the differences in the study design, the sample size, the heterogeneous study population, as well as intrapartum usage of oxytocin and analgesia [8, 11]. Prospective, multicenter, large-scale trials are needed to elucidate the characteristics of labor in women with VBAC.
Considerable attention had been paid to the durations of labor in VBAC women with and without cervical dilation in their prior labor. And we found VBAC women with cervical dilation showed comparable first and total stage of labor than multiparae. However, compared with primiparae, we found VBAC women without cervical dilation showed shorter first and total stage of labor. The reduced cervical resistance to dilatation in parous women might account for the differences .
As for the second stage of labor, we found it was shorter in VBAC women than that in primiparous women, but longer than that in multiparous women, which was in agreement with the previous study . Likewise, women who underwent VBAC without cervical dilation showed a shorter second stage of labor than primiparae, while those with cervical dilation showed a longer one than multiparae. It might be related to the loss of pelvic floor contractility in prior pregnancy . There is little research on the third stage of labor, and we found that the third stage of labor was shorter for VBAC women than for multiparae. Similar results were discovered between VBAC women with cervical dilation and multiparae. However, no difference in the third stage of labor was found between VBAC women and primiparous women, and between VBAC women without cervical dilation and primiparous women. This might be because our midwives paid more attention to the women with VBAC and took more active measures to prevent the occurrence of postpartum hemorrhage, resulting in early delivery of the placenta in the third stage of labor.
Usage Of Interventions During The Labor
Oxytocin and artificial rupture of membrane are routine methods to strengthen contractions and accelerate labor whenever required, which was associated with increased rates of uterine rupture during VBAC [5, 11]. Our study analyzed the rate of oxytocin usage and the rate of artificial rupture of membrane (AROM) among VBAC women, primiparae and multiparae. The results showed that the rate of oxytocin and AROM usage in VBAC women was lower than those in primiparae but comparable to those in multiparae, which was consistent with a previous study . However, Grylka-Baeschlin et al. found the women with VBAC received oxytocin significantly less often than primiparae, but more often than multiparae . Given the dose-dependent relationship between oxytocin use and uterine rupture , low-dose oxytocin is safe and effective in VBAC.
Phloroglucinol is recommended to facilitate labor not only by reducing spasms and edema of the cervix but also by harmonizing shrinkage of the uterus . Besides, Tabassum et al. found that pain intensity seemed lower in laboring women who received phloroglucinol as compared to those who received placebo . This might be because pain during the delivery mainly comes from dilation of the cervix and contraction of the uterus. Phloroglucinol, as one of the spasmolytics and spasmoanalgesics, also showed few side effects in both mother and fetus [16, 26 ]. The fear of masking the pain of a uterine rupture had made the use of epidural anesthesia a dilemma . Our data showed women with successful VBAC had a lower rate of epidural analgesia than primiparae but was comparable to multiparae, which was similar to a former research . Conversely, the women with VBAC were more likely to use phloroglucinol than multiparae, but not primiparae. Furthermore, the rate of phloroglucinol usage in the VBAC women with cervical dilation before the previous cesarean section was similar to that of multiparae, while the rate of phloroglucinol usage in the VBAC women without cervical dilation before the previous cesarean section was similar to that of primiparae, which might be because they have similar cervical conditions. Epidural analgesia is encouraged for women undergoing TOLAC to provide pain control without increasing the risk of postpartum bleeding or uterine rupture . The rate of epidural analgesia might be related to different durations of labor in women between groups.
Some studies demonstrated prolonged labour, especially the prolongation in the second stage of labor, was associated with multiple adverse maternal and foetal outcomes such as obstructed labour, postpartum haemorrhage, perineal injuries [4, 16, 17]. To shorten the second stage of labor, forceps and episiotomy were frequently used for operative vaginal delivery . Our study showed that episiotomy were more common for VBAC women compared with multiparous women and primiparous women, which was in agreement with a recent study . But there was no significant difference in the rates of forceps deliveries among VBAC, primiparae and multiparae in our study. And Madi JM et al.  found the rate of forceps deliveries was 5.3% in women who underwent VBAC, which was similar to our result (3.6%). Forceps-assisted vaginal deliveries are associated with maternal adverse outcomes such as sphincter damage, pudendal nerve damage, third- and fourth-degree perineal laceration, as well as neonatal adverse outcomes like subdural or cerebral hemorrhage, facial-nerve injury, brachial plexus injury, and the increased rate of mechanical ventilation [12, 17, 18, 19]. Consequently, the use of forceps should be minimized whenever possible in current study, and to avoid uterine rupture by shortening the second stage of labor might be the reason for the increased rate of episiotomy usage in VBAC women. In contrast, Zdenek Rusavy et al. found that primiparous women and multiparous women had comparable rates of episiotomy to women with VBAC . The differences may be explained by differences in the discretion of obstetricians and indications for episiotomy.
Maternal And Neonatal Outcomes Of The Study Groups
Previous studies had shown a positive correlation between perineal lacerations and operative vaginal deliveries, but most of these studies concentrated on third- and fourth-degree perineal tears [2, 9, 18, 20]. Our study included perineal lacerations from first- to fourth-degree, and the result was consistent with the observation reported elsewhere,  showing a higher risk of spontaneous perineal tears in VBAC women and VBAC women without cervical dilation compared to the primipara control group. A possible explanation is related to the faster progress in labor in VBAC women, which when coupled with the nulliparous pelvic floor in these without cervical dilation may lead to higher risk of perineal rupture [9, 18].
Postpartum hemorrhage (PPH) can be caused primarily by atony uterus, retained tissue, genital tract tear, coagulation problem, and uterine rupture . Previous studies had almost focused on the rate of PPH in VBAC and elective repeat cesarean delivery, and found PPH occurred more often in VBAC and mothers with PPH were exposed to more blood transfusion [11, 22, 23]. This was the first time to compare the rate of PPH between women who underwent VBAC and vaginal delivery. Our study showed a higher rate of PPH in VBAC than primiparae and mulriparae. We also found there was more blood loss during and after VBAC within two hours than primiparae and multiparae delivered by vaginal. However, some studies revealed VBAC was associated with a lower incidence of PPH and was considerably less expensive than repeat cesarean section [2, 3, 4]. That’s probably because, with the increase of parity and gravidity, women’s myometrial muscular strength may get reduced due to the reduction of collagen fibers, especially in women with a history of cesarean section . To reduce the occurrence of PPH, effective labor management such as actively prepared blood, uterus massage and drug therapy should be encouraged in VBAC women.
With regard to infectious complications, maternal fever was more common in VBAC than elective repeat cesarean delivery [6, 13]. Rita E. Fisler et al. found the increased rate of maternal intrapartum fever was associated with the use of epidural analgesia, resulting in adverse neonatal outcomes . However, the relationship between epidural analgesia and the rate of maternal intrapartum fever in our study was not clear. And few data was found in comparing the rate of maternal fever in women with between VBAC and vaginal delivery. Our research found no differences between women who underwent VBAC without cervix dilation before the previous cesarean section and primiparae, women who underwent VBAC with cervix dilation and multiparae, women who underwent VBAC and primiparae. However, intrapartum fever occurred more often in women with VBAC than multiparae, which might be the result of the prolonged labor.
Few previous studies have investigated postpartum urinary retention in VBAC women. It was the first time to find there was no significant difference in the occurrence of postpartum urinary retention in VBAC women, primiparae and multiparae. Regarding the postnatal condition of the newborn such as neonatal asphyxia, Apgar score in 1st minute plays an important role. No significant difference was found in women who had normal spontaneous vaginal delivery as compared to women who had VBAC , which was in agreement with our study. A previous study indicated that compared with a trial of labor, there was a higher rate of transient tachypnea of the newborn after elective repeat cesarean section . This condition is due to delayed clearance of fluid from the lung at the time of birth and results in some degree of respiratory distress. Therefore, VBAC may reduce the occurrence of neonatal asphyxia.
Strengths And Limitations
The major strength of the present study lies in its design. Unlike most previous studies on this topic, our study took cervical dilation prior to the cesarean section into account. And it was the first time to compare durations of labor, intrapartum interventions and perinatal outcomes between VBAC women without cervical dilation before the previous cesarean section and primiparae, and between VBAC women with cervical dilation before the previous cesarean section and multiparae, respectively. Besides, we found a remarkable resemblance between women who underwent VBAC with and without cervical dilation in their prior labor respect to the results. Therefore, TOLAC is well recommended in women without contraindications of VBAC. The major limitation of the study is certainly the number of women in our groups, however, the size still allowed a proper statistical analysis. Naturally, the survey is slightly incomplete as all the necessary information could not be gathered. Another limitation is that there might be some missing data in such a retrospective study.