Factors affecting success of trial of labour after previous one lower segment Caesarean section

Objective: The aim was to analyze the different factors associated with successful trial of labor after previous one lower segment cesarean delivery in our institution. Patients and methods: A Prospective case-series study was done at Al-Batool Maternity Teaching Hospital, Mosul on 476 women with previous one lower segment Caesarean delivery subjected to trial of labour between January 2009 and mid June 2009. Results: Successful trial of labour and vaginal delivery was reported in 82%. The factors that were found to be significantly associated with successful trial of labour are: parity of 2-4, history of previous vaginal delivery and particularly history of vaginal birth after Caesarean, fetal malpresentation as the indication of previous Caesarean, inter-pregnancy interval longer than 12 months, gestational age ≤ 40 weeks, cervical dilation ≥4 cm, cervical effacement ≥50%, station lower than –1 and intact membrane at time of admission, clear liquor and neonatal weight < 4000 grams. Conclusions: The factors present in woman's obstetric history and during her intrapartum course in the current pregnancy and birth weight that had significant differences in this study can be used as predictor of successful trial of labour and will help obstetrician to identify women who are more likely to attempt trial of labor and have a successful vaginal birth after previous one lower segment Caesarean delivery.

aginal delivery after previous one lower segment Caesarean section represents one of the most significant and challenging issues in obstetric practice (1) and it has been accepted as a way to reduce the overall Caesarean section rates (2)(3)(4)(5) and elimination of the need for major surgery which consequently reduces maternal and neonatal morbidity and mortality as well as reduce the financial and psychosocial disadvantages (6)(7)(8) .Trial of labour (TOL) was recommended by the American Academy of Family Physicians (9) and Society of Obstetricians and Gynaecologists of Canada (10) as Level A and the universal adoption of Craigin's dictum of once a Caesarean, always a Caesarean made in the old obstetric days will be no longer applied (2,6) .Although numerous publications over years have demonstrated the relative safety and efficacy of TOL (2)(3)(4)6,12) , it may be occasionally associated with severe maternal morbidity and even mortality (1) and the risk depends on the success of TOL (2,4,13) as adverse outcomes are most common following a failed TOL (1,7,13- 15) and women are at increased risk of emergency Caesarean section, uterine rupture, infectious morbidity, hemorrhage and perinatal death (2,4,14) .
Several studies have found that many factors (clinical characteristics and obstetric variables) are associated with TOL failure (2,4,12,13) and some have proposed different scoring systems to incorporate these individual factors and attempt to reliably predict TOL success, failure, or complications (12) as this would help clinicians and women in making good clinical decisions and minimizing adverse events (2,7,14) .The aim was to analyze the different factors associated with successful trial of labor after previous one lower segment Caesarean delivery in our institution.

Patients and method
A prospective case-series study was carried out in Al-Batool Maternity Teaching Hospital in Mosul city, which is a tertiary referral center and it operated an open door policy where all pregnant women, booked and unbooked, were seen and managed, irrespective of their clinical state.Blood bank, laboratory facilities, radiology services, operating theatres and neonatal intensive care support are available at any time.A trained obstetrician, obstetric registrars, anesthetic doctor and a neonatal registrar being on duty around the clock.The total number of annual deliveries (including vaginal delivery and operative delivery) were 23257.The study started from January 1 st till June 15 th 2009.A 476 women with previous one lower segment Caesarean delivery were included in the study that deemed suitable for TOL (singleton pregnancy with vertex presentation and no contraindication for vaginal delivery such as: previous uterine rupture, placenta previa).
Patients admitted in labour for TOL were managed using partograph for their progress of labour and were monitored carefully.Pinard's stethoscope and intermittent electronic fetal monitoring were used to monitor the fetal heart rate as there was no enough number of machines for continuous monitoring in the labour ward.Women who had either meconium stained liquor or bloody liquor were allowed to undergo TOL if they have advanced cervical dilatation and reassuring cardiotocographic (CTG) trace and no vaginal bleeding to endanger mother and/or fetal life; these TOL were done under close observation and monitoring with low threshold for Caesarean delivery.These cases after delivery were divided into 2 groups: successful TOL group who delivered vaginally and failed TOL group who required an emergency Caesarean delivery.The association of various factors with success of TOL was analyzed statistically.These factors were socio-demographic characters (maternal age, parity, address), past obstetric history characters (history of prior vaginal delivery, history of previous vaginal birth after Caesarean (VBAC), history of previous fetal loss , inter-pregnancy interval, indications of previous Caesarean delivery), current pregnancy and intrapartum characters (booking state, history of hypertensive disorder with pregnancy and diabetes mellitus, gestational age, type of labour (spontaneous or induced), need for augmentation, cervical os dilatation, cervical effacement, head station, state of membranes at the time of admission,

Statistical analysis
Student T-test and Chi-square test were used for statistical analysis.Odds ratios (OR) and their 95% confidence intervals were also calculated.The Minitab version 11 SPSS was used for statistical analysis.P value <0.05 was considered significant.

Results
Among 476 pregnant women who underwent TOL after previous one lower segment Caesarean delivery,391 women (82.15%) delivered vaginally (successful trial group), while 85women (17.85%) delivered by emergency Caesarean section (failed trial group).
There was no maternal death in this study but there were two scar dehiscence (0.4%) that required emergency operation and successful repair of uterus were done without major complications; the patients had an uneventful recovery and both neonates had Apgar scores of 9 at 5 minutes.
Table (1) demonstrates that there was no significant difference in maternal age and address between the successful and failed TOL groups.
Regarding past obstetric characteristics, the following factors were significantly associated with successful TOL as shown in table (2).Women who were giving more than one viable pregnancy (Parity >1) particularly those women with parity 2-4 as their TOL were associated with more vaginal delivery while those women with parity ≥5 were associated with more emergency Caesarean delivery.
History of prior vaginal delivery (vaginal delivery before and after Caesarean delivery) was highly significant among success group and specifically those who had history of previous VBAC (p value: 0.004, OR=0.35; 95% CI: 0.18-0.71).A past history of fetal loss didn't make any difference to the mode of delivery as most of cases were due to abortion (83.95%).When the interval between the previous delivery and the current pregnancy was longer than 12 months, more success of TOL were reported.Studying the indication of previous Caesarean delivery showed fetal malpresentation (non recurrent cause) was associated with more success TOL while failure to progress of previous labour (recurrent cause) was associated with failed TOL.Both fetal distress and placental causes had no significant associatation with success TOL.In the evaluation of current pregnancy and intrapartum characteristics, booking status, hypertensive disorder with pregnancy and diabetes mellitus showed no significant difference among both groups.Gestational age ≤40 weeks (p value 0.002), cervical dilatation of ≥4 cm, cervical effacement of ≥50% , a station of -1 or lower and those with intact membrane at time of admission and clear liquor were more likely to have a successful VBAC and they were statistically significant among success group.Type of labour (spontaneous or induced) and use of oxytocin were not statistically differed between both groups as showed in table (3).
After delivery, newborns who delivered by vaginal delivery had weight of < 4000 grams which was significantly differ from those delivered by Caesarean section (p value 0.000).There was no significant difference between both groups in sex of newborns as demonstrated in table (4).

Discussion
The advantage of a trial of labor and vaginal delivery compared to repeated Caesarean section is well established (3,4,6,11) , and it was apparent in localities like Iraq, where there is a tendency towards large families, as it allows women to have multiple deliveries without the potential for multiple repeated Caesareans (7) which is associated with an expected rise in complications and difficulty in performing surgery due to adhesions, and the risk of damage to the bladder (15) or bowel at the time of surgery as well as there may be difficulties in conceiving a further child or the development of placenta praevia or accreta (7,15) and increased chances of uterine rupture (7) in the future pregnancy.In addition, strategy of TOL in hospital may encourage women to attend hospital for delivery than home delivery (1) .The rate of vaginal birth after trial of labour was 82% in this study, near to that rate reported in Baghdad (86%) (16) and in Jordan (80%) (11) and it was higher than the rates reported in a 2003 literature review of 142,075 trials of labour(70%) (3) and 59% in New Guinea (6) but less than 91% reported in Korea (5) .
Although some studies (5,11) reported no case of uterine rupture in women who had undergone TOL after Caesarean delivery, recent large review of studies (3) done in different places quoted the range of uterine rupture as 0.4%-0.62%,which means that our two cases (0.4%) of dehiscence scar were in the range of others and it was lower than 1.5% reported in Aisien et al study (1) .
There was no maternal mortality in most of studies (5,6,11,14) done elsewhere as well as in this study unlike Aisien et al study (1) who reported one maternal death due to uterine rupture and postpartum haemorrhage.
In this study, Maternal age showed no effect on mode of delivery similar to other studies (6,12,13,17) , but differ from Bujold et al study (18) which showed increasing failure of TOL in women who were 35 years and older.
Residence in this study showed no effect on the success of TOL as cases with obstructed labour (which mainly arrived from rural area) were not included in this study.We can't compare residence with other studies as they studied effect of race, not address, which can't be applied in our locality as we have no different races nor immigrant.
Parity more than one made women more likely to have successful TOL in this study which is in agreement with other studies (6,8) .Multiparous women (para 2-4) was delivered vaginally more than grand multiparous women (para ≥5) and can be explained by the fact of the tendency of babies to get bigger with parity, increasing incidence of malpresentation and increasing soft tissue scarring with increasing parity (6) .
Successful TOL has been found to be influenced by previous vaginal delivery, particularly, a prior VBAC (7,12,13,19) which is in agreement with this study.
Reports in the literature (3,12,20,21) have shown a significant effect of the indications of previous Caesarean delivery on success of TOL.In this study, more success of TOL was reported among women with fetal malpresentation as an indication of previous Caesarean delivery which was corresponded with Tripathi et al study (21) .In the other hand, failure to progress of labour in previous pregnancy was reported to be associated with less success of TOL in this study which was reported in other studies (4,6,21) .Fetal distress does not appear to affect mode of delivery in this study in contrast with others (4,21) .The inter-pregnancy interval was longer among success group in this study while failed to be shown in Stamilo et al study (23) .Our result regarding past obstetric history of fetal loss corresponded with the result noted in Amoa et al study (6) as there was no significant effect on success of TOL as most of them were due to abortion not to fetal death.
In the evaluation of the current pregnancy, there was no difference in the mode of delivery between booked and unbooked women who were subjected to TOL which not correspond with Asian et al study (1) .There was no apparent effect of presence of hypertensive disorder with pregnancy and diabetes mellitus on the success of TOL as many of these women were subjected to elective repeat Caesarean section and not allowed to go to labour which correspond to many studies (6,12,21) but not with others (3,22) .
Gestational age >40 weeks was associated with more failure of TOL which was shown in other studies (4,8,17,24) which can be explained by increasing birth weight, increased risk of fetal intolerance of labor and increased need for induction of labor as gestational age advanced after 40 weeks while some other studies (3,17,21) failed to show this association.This study failed to show any effect of preterm gestational age on mode of delivery which differ from other studies (6,12,25) .
In our very crowded hospital, most of obstetricians didn't use oxytocin in induction or augmentation of trial of labour after previous one lower segment Caesarean delivery because they feared from the high morbidity and mortality associated with uterine rupture.For that reason, only eight inductions with oxytocin and twenty one labour augmentations with oxytocin reported in this study with no scar rupture and no perinatal loss.Evaluation of these cases showed no significant association between induction of labour and augmentation of labour with more failure of TOL which does not confirm with other studies (4,12,13,20) as these studies evaluate more cases and difference in induction methods.
Not surprisingly, the more advanced the cervical dilatation in initial presentation, the higher the rate of successful TOL which is shown in this study and in agreement of other studies (5,6,13,17) .Cervical effacement ≥ 50% and head station -1 or lower more likely to deliver vaginally as in other studies (4,5,6,13) .
In this study, rupture membrane diagnosed at time of admission was associated with more failure of TOL and meconium stained liquor was another strong predictor (OR 8.36; 95% CI 5.23 -13.37) of emergency Caesarean sections in agreement with Tan et al study (3) while other studies (4,21) failed to show any effect.
In this study, as other studies (3,4,6) , sex of the newborn in the current pregnancy didn't have any significant effect on the success of TOL.

Conclusion
The factors present in women's obstetric history and during her intrapartum course in the current pregnancy and birth weight that had significant differences in this study can be used as predictor of successful trial of labour and will help obstetrician to identify women who are more likely to attempt labor and have a successful vaginal birth after previous one lower segment Caesarean delivery.

Table ( 1
): Sociodemographic characteristics and mode of delivery.

Table ( 2
): Past obstetric characteristics and mode of delivery.

Table ( 3
): Current pregnancy with intra-partum characteristics and mode of delivery.

Table ( 4
): Neonatal characteristics and mode of delivery.