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Maternal Outcome Of Induction Of Labour
ABSTRACT A prospective study at Maternity Hospital over a two and half months' period in the year 1998/99 was performed to study the relationship of Bishop score (BS) prior to induction of labour (IOL) with the outcome of induction by oxytocin infusion.
Hundred and three women were studied, 48 were in the low BS group (0-4) and 55 were in the high BS group (5-8). There were no significant differences in features like age, gestational age, socio-economic status and indications of induction between the two groups.
The rate of induction during the study period was found to be 3.7%. The overall failure of induction was 25% and failure was significantly higher in low BS group than in the high BS group (43.7% versus 9%). There was significant difference in the rate of vaginal delivery between the two groups, and the caesarean section (CS) rate was also not identical. Caesarean delivery occurred more frequently in the low BS group than in the high BS group (23% Vs 14.5%); and the difference was significant statistically too. Nulliparas in both the study groups had higher CS rate as compared to multiparas. The time required to achieve vaginal delivery after induction was greater in women who had low BS than in women with high BS (11.16 hrs Vs 9.02 hrs). The complications of induction were very few in both the groups and not significantly different between the groups except for post-partum haemorrhage (PPH) which was significantly higher in the low BS group (11% Vs 0%). Very few had maternal complications (11.2% in low BS Vs 12% in high BS group).
To conclude, the women with a low Bishop score had a poor outcome of induction in the present study. They had higher failure rate, higher caesarean section rate, longer mean induction delivery interval, higher maternal complications (PPH). Keywords: Maternal outcome, Induction of labour, Bishop score, Caesarean section. INTRODUCTION Induction of labour is often carried out for various maternal and/or fetal reasons. It is the artificial initiation of uterine contractions prior to their spontaneous onset leading to progressive dilatation and effacement of the cervix and delivery of the baby, after 28 weeks of gestation.1 In other words it implies stimulation of contractions before spontaneous onset of labour, with or without amniotomy.2
The aim of successful induction is to achieve vaginal delivery when continuation of pregnancy presents a threat to the life or wellbeing of the mother or fetus.3, 4 The success of any method of induction depends on the parity, the gestational age and the state of cervix at the beginning of induction. The success of induction depends largely on the cervical status at the start of the induction process.5 Bishop in 1964 devised a useful practical scoring system to assess the state of the cervix prior to the induction of labour.6 In most centres, Bishop's score or a modified version of it is used to assess the favourability of the cervix. Despite the safety of induction, a liberal induction policy leads to an increase in operative deliveries creating potential risks for the mother and the child and greater expense. In addition to this, failed induction may be associated with a poor neonatal outcome and/or long labour with physical and emotional disturbances for the mother.4 Induction in the presence of an unripe cervix results in a longer labour and a higher incidence of caesarean section and fetal asphyxia.7
The purpose of the present study was to know the pregnancy outcome of induction in our pregnant women and to compare the outcome between the women with an unfavourable (BS£4) and a favourable cervical score (BS > 5-8). The maternal outcome of the induced labour in our set up may guide us to plan the management e.g. priming of the unfavourable cervix prior to induction and anticipating and handling any complication in a better way. The fetal outcome is described in another paper.8 materials and methods: This study was a hospital based analytical study. It was conducted at Maternity hospital located at Thapathali, Kathmandu. It has 302 beds, where total number of delivery is around 14000 each year and a caesarean rate of 9.6% 9,10 The duration of the study was two and a half months, starting from 31 July, 1998 to 15 Sept. 1998 and 16 May 1999 to 15 June 1999.
Hundred and three women were included in the study, 48 were in the low BS group and 55 were in the high BS group (study groups). There were 29 nulliparas (60%) and 19 multiparas (40%) in the low BS group (n=48). Similarly, 43 nulliparas (78%) and 12 multiparas (22%) were included in the high BS group (n=55). All pregnant women except grand multipara (>4 viable deliveries) with alive singleton pregnancy of gestational age of 37 or more weeks with cephalic presentation were included in the study. Women with pre-labour rupture of membranes (PROM) and /or previous caesarean delivery were excluded from the study. These patients were categorized by Bishop scores at the beginning of induction for comparison of pregnancy outcome. Women undergoing induction with low Bishop scores (0-4) were grouped in one study group, and those with high Bishop scores (5-8) into another. Induction procedure: All the patients were induced by oxytocin infusion according to the Maternity hospital protocol.10None of our subjects received prostaglandin gel to ripen the cervix and none were given epidural analgesia during labour. In the present study the traditional protocol of high dose oxytocin infusion by titration method was utilized by using a standard administration-set, 15 drops per minute equals a rate of 1 ml. per minute.
None were monitored by CTG and fetal blood sampling was not done. If membranes had not ruptured spontaneously, artificial rupture of membrane was generally performed when the cervix was 3-4 cm dilated in established active labour. Infusions were discontinued if there was fetal tachycardia, bradycardia or persistent abnormal FHS and managed appropriately. The infusion was discontinued also in case of failed induction. Failed induction was defined as inability to enter into the active phase of labour despite oxytocin stimulation for a total of 12 hours. Patients, who did not go into active labour following the 12-hour of oxytocin infusion, were managed at the discretion of their attending obstetricians. After delivery the infusion was continued for one hour as prophylaxis against PPH.
Details of obstetric history, examination, age, parity, gestational age assessment, cervical scores (BS), indications of induction, induction delivery interval (IDI), mode of delivery, indication for operative delivery, maternal complications and neonatal outcome were documented. Statistical analysis of variables was done using the X2 test and the Student t test. A two tailed P value less than 0.05 was considered to indicate a significant difference.11 RESULTS: Over the two and a half months' study period, the induction rate was 3.7%. One hundred and three women were entered into the study, 72 (70%) were nulliparas and 31 (30%) were multiparas.
The patients were stratified by Bishop score at entry for further analysis. Forty-eight (46.6%) women had low BS (0-4), whereas fifty-five (53.4%) had high BS (5-8). The mean BS in low BS group and high BS group was 3.72 and 6.01 respectively. TABLE I: PATIENTS CHARACTERISTICS
· Numbers in parentheses indicate numerator and denominator of percent. · NS: Not Significant S: Significant As summarised in Table I, there were no differences between the two study groups with regards to maternal age, gestational age at induction and antenatal attendance.
Post-dates (Overdue by dates, post - EDD) was the leading indication for induction, comprising of 64.58% women among low BS group and 76.36% women in high BS group. The indications were similar in both the study groups, the difference being not significant statistically. TABLE III: OUTCOME OF INDUCTION ACCORDING TO BISHOP SCORE
· The overall failure rate was 25.2% (26/103). The failure rate was significantly higher (P=. 0000) in the low BS group than in the high BS group. The vaginal delivery rate was lower in the low BS group whereas the CS rate was higher in the low BS group. Thus, the women with low BS had high failure rate and more operative delivery rate in the present study. TABLE IV: MEAN IDI IN RELATION TO BISHOP'S SCORE (Controlled for parity)
· Cases in which CS was performed were omitted in calculation of the IDI. · Data presented as mean ± SD. The women with low Bishop's score had significantly (p=0.0281) longer mean IDI than those with high BS (11.16 hr Vs 9.02 hr). Nulliparas in both the groups had longer mean IDI than that of multiparas. So, parity was inversely related to the mean IDI. Thus nulliparous women with low BS had longer mean IDI in the present study. TABLE V: MODE OF DELIVERY IN RELATION TO BISHOP SCORE
· Cases of failed induction were omitted in calculation of mode of delivery.
Vaginal delivery rate was significantly higher (P=0.0162) in the high BS groups as compared to the low BS group. However, the CS rate was significantly lower (P=0.0162) in the high BS group than in the low BS group. Therefore, women with high BS at induction had better outcome as compared to those with low BS at induction. TABLE VI: DISTRIBUTION OF LSCS ACCORDING TO BISHOP SCORE (Controlled for parity)
· Cases of failed induction were omitted in calculation of LSCS. In total, about 40% women in the low BS group had LSCS, whereas only 16% women in the high BS group had LSCS. The difference is significant (P=0.0162) statistically. On parity-wise analysis, in the low BS group nulliparas had significantly higher (P=0.0426) CS rate as compared to multiparas. In the high BS group also nulliparas had significantly higher (P=0.0057) CS rate as compared to multiparas. Thus, nulliparas in both the groups had higher CS rate, as compared to multiparas. TABLE VII: MATERNAL COMPLICATIONS IN RELATION TO BISHOP SCORE
· Cases of failed induction were omitted in calculation of complications. The majority did not have complications in both the study groups. Women with low BS did not have pyrexia and genital tract injury but the difference was not significant statistically (P=0.5478). Eleven percent in the low BS group had PPH, but none had PPH in the high BS group. The difference was significant statistically too (P=0.0399).
DISCUSSION: In the present study with the induction rate of 3.7%, various outcome parameters of induction of labour were studied. The rate of induction varies greatly. A rate of 4% in one centre in Britain compared to 40% in another centre exemplifies the variation 12. The reason for a low rate in our study was not clear but it might be due to obstetricians' reluctance of induction unless there is a valid indication. In a Singaporean study, the induction rate was 9.8% 13 and in a recent survey from Finland it was 19.5% 14. Similarly in an Indian study, the rate was 11.4% 15.
Indications for induction are fetal, maternal or both and at times social. Fetal reasons constitute the large majority of indications. The indications for 103 cases of induction of labour in the present study are shown in table II. In the present series, the major indication was post-dated pregnancy with a 70.8% of all induced labours followed by HDP (11.6%), niggling pain (10.6%), less fetal movement (4.8%) and others (1.9%). The indications did not differ significantly by Bishop category in both the study groups. In a Finnish study, HDP (40%) was the most common indication followed by post-dated pregnancy (27.5), intra-uterine growth retardation (11.5%), fetal deaths (5%) and others 14. But, in an Indian study, the indications were mainly post-term pregnancy (72%) and uncontrolled hypertension (25%) 15. In Arulkumaran and his colleagues' study, static weight or weight loss at term was the major indication of induction comprising 33.7% of induced patients, followed by mild pre-eclampsia (22.7%) and prolonged pregnancy (9.5%) 13. In our study, post-date was major indication. This might be due to the practice of early induction at 40+ weeks by the obstetricians, which may be because of lack of facilities for intensive fetal surveillance for post-dated pregnancies.
In the present study, the overall failed induction rate was 25.2% (26/103), and majority of the failures was in the nulliparous women (20%). When analysed by the Bishop score, 43.75% of the low BS group patients experienced failure compared to only 9.09% of those from the high BS group. This is shown in table III. Parity showed a strong relation to the success of induction. In a Singaporean study, overall failed induction rate was 7% in-patients induced with amniotomy and syntocinon 13.
The higher failure rate in the present study may be because of higher number of nulliparas included in this study, lack of use of cervical primers like prostaglandin prior to induction and delayed amniotomy only in the active stage of labour.
Bishop score at induction and parity are important factors, which influence the mean induction delivery interval. This was well demonstrated in the present study. The women with a low BS had significantly longer IDI as compared to women with the high BS (11.16 hrs Versus 9.02 hr). Nulliparas in both the study groups had longer mean IDI than multiparas as shown in table IV. In a study of primigravidae whose labour was induced by amniotomy and oxytocin, it was found that the mean IDI was higher in women with a low cervical score of 0-3, than in women with high score of 4-7 (14.9 hrs Versus 8.9hrs) 7. Pant et al found that the BS was directly related to the mean IDI. In their study, the women with a low BS (0-4) had a mean IDI of 12.30 hrs and those with a score of 5-8, had a mean IDI of 9.5 hrs16. In agreement with our study, many studies also showed a longer IDI in nulliparous women than in multiparous women. Mukherjee et al reported the mean IDI, in women with the BS of less than 5, to be 22.5 hrs and 12.4 hrs in primigravidas and multigravidas respectively17. Similarly, Mishra et al found mean IDI to be 11.35 hrs in primigravidas and 7.99 hrs in multigravidas, all of them had a pre-induction BS of less that 3 15.
A Singaporean study showed the mean length of labour in women with low cervical score (0-3) to be 10.8 hrs and 7.1 hrs in primigravidas and multigravidas respectively. Similarly in 4-6 scores group it was 8.6 hrs and 5.2 hrs in primigravidas and multigravidas respectively 18.In those studies, the mean IDI was longer in patients with low score at induction, may it be Bishop score or its modified version. This also applied equally to the present study in which women with low BS had significantly longer IDI than those with high BS.
Thus the greatest maternal risk of induction of labour is the risk of morbidity associated with CS for various reasons and the risk increases with the decrease in parity and also with the decrease in the favourability of the cervix at induction. This was well demonstrated in the present study in which the CS rate was significantly higher in women with low BS group than in the high BS group (23% Versus 14.5%) as shown in table III and nulliparas in both the groups of the study had a higher CS rate as compared to multiparas, as shown in table VI. These findings are consistent with the findings of many studies from various parts of the world. Pant et al reported a CS rate of 40% in induced labour with a low BS (0-4) score and a CS rate of 15% in women with BS of 5-816. The findings of their study are close to that of our study but prostaglandin and initial amniotomy were not used in the present study.
In a study of primigravidas whose labour was induced by amniotomy and oxytocin, the CS rate, in women with a low cervical score (0-3) was reported to be 32% where as it was only 4% in women with a score of 4-7. That study used cervical score instead of BS and only primigravidas were studied.7 Macer et al reported that the BS did not affect the CS rate for multiparous women. However nulliparous women with a BS £ 5 had higher CS rate than those with BS > 5, 50% compared with 26%19.
Mishra et al in a study of induced labour with modified BS of 0-3, reported the CS rate of 47.2% and 14.6% in primigravidas and multigravidas respectively 15. In a study by Kurup et al, the CS rate was 48.6% in those with a poor cervical score (£5) compared with 8.8% in those who had a good score (³ 6) 20. In a study carried out in Singapore the CS rate in multiparas and nulliparas with a good cervical scores (7-10) was not high. However nulliparas with a cervical score of 3 or less had a CS rate of 65% for all indications (45.8% for failed induction). Multiparas with the same cervical score (< 3) had a CS rate of 7.7% only. In the same study, nulliparas with a cervical score of 4-6 had a CS rate of 10.3%, whereas multiparas with cervical score of 4-6 had a CS rate of 3.9%. In that study nulliparas had a higher CS rate than multiparas and women with low score had higher CS rate18.
The vaginal delivery rate including the instrumental delivery was higher in the high BS group than in the low BS group (84% versus 59%) in our study. Calder found the vaginal delivery rate of 68% in women with low pre-induction cervical score (0-3) and 96% in women with a score of 4-77. Pant et al reported the vaginal delivery rate in women with a low BS (0-4) was lower than in women with a high BS (5-8) (60% Versus 84%) 16. These findings are quite close to our findings in the present study. Another study of oxytocin induced labour in women with a low modified BS (0-3) showed a vaginal delivery rate of 52.8% and 85.4% in the primigravidas and multigravidas respectively.15
Many studies of induced labour showed some maternal complications of induction by oxytocin infusion. In the present study, the majority did not have complications in both the study groups (88.8% in low BS group versus 80% in the high BS group). Women with low BS did not experience pyrexia and genital tract injury but 11% women in this group had PPH, which was significant. In the high BS group, few women had pyrexia and genital tract injury and none had PPH.
In a study of induced labour by Xenakis et al maternal complications associated with induction were infrequent and did not differ by Bishop category. Chorio-amnionitis was the most common complication occurring in 3.5% of the 0-3 Bishop score group and 4% of the 4 and above Bishop group. All other complications (hyperstimulation, PPH, hysterectomy) occurred in 2% or less population. Overall 93% of the women experienced no complication.21 In an Indian study, vomiting was observed in 4.8% and hyperstimulation in 9.5% women with low BS (<5) induced by oxytocin.22 Other studies showed the side effects of oxytocin in induced labour were rare.7, 17
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