Keywords
induction of labor - cesarean section - robson classification
Palavras-chave
trabalho de parto induzido - cesárea - classificação de Robson
Introduction
Induction of labor (IL) is a common obstetric procedure, and the number of cases in
which labor is induced seems to have been rising in the last decades.[1] Induction of labor should be considered whenever the risks of the pregnancy outweigh
its benefits, for either the mother or the fetus.[1]
[2]
[3]
[4] Approximately 9.6% of all deliveries result from IL, but in industrialized countries
this number is estimated to be ∼ 25%.[1] The choice between multiple methods for IL, from mechanic to pharmacological, should
be based on the clinical situation and the available resources. Since it is not a
risk-free procedure, it should not be performed without a formal and reasoned medical
indication.[5]
In the past few years, many studies have aimed to evaluate the cesarean section (CS)
rates after IL. Unlike previous results, more recent studies described a reduction
in CS rates after IL in term pregnancies, without an increment on perinatal morbidity.[6]
[7]
[8] However, there are significant differences between the considered populations and
the applied methodologies, making the results of those studies inconsistent and controversial.[4]
[6]
[7]
[8]
[9]
The progressive increase of CSs performed worldwide has become a major public health
concern and multiple strategies have been discussed to reduce it.[10]
[11] Similarly to what happened in other countries, the Portuguese health board also
adopted the Robson Classification System (RCS) in 2015.[12]
[13] This classification system ([Table 1]), initially created and proposed as a clinically relevant, reproducible and prospective
instrument for evaluating, monitoring and comparing CS rates, has been recently used
for other purposes.[14]
[15]
Table 1
Robson classification system
|
Group
|
Description
|
|
1
|
Nulliparous, single cephalic, ≥37 weeks, in spontaneous labor
|
|
2
|
Nulliparous, single cephalic, ≥37 weeks, induced or CS before labor
|
|
3
|
Multiparous (excluding previous CS), single cephalic, ≥37 weeks, in spontaneous labor
|
|
4
|
Multiparous (excluding previous CS), single cephalic, ≥37 weeks, induced or CS before
labor
|
|
5
|
Previous CS, single cephalic, ≥37 weeks
|
|
6
|
All nulliparous breeches
|
|
7
|
All multiparous breeches
|
|
8
|
All multiple pregnancies (including previous CS)
|
|
9
|
All abnormal lies (including previous CS)
|
|
10
|
All single cephalic, ≤36 weeks (including previous CS)
|
Abbreviations: CS, cesarean section.
In our institution, we perform around 2,300 deliveries per year, and we routinely
classify all women in labor according to the RCS. In 2016, our CS rate was 24.3% and
the IL rate was 26.9%. One third of all CSs performed were elective. In the present
study, we have aimed to evaluate the impact of IL in the overall CS rate, as well
as to analyze CS rates according to the method of IL employed and to the Robson group
in which it was applied.
Methods
The department of obstetrics and gynecology of the Hospital de Santa Maria, Centro
Hospitalar de Lisboa Norte, Lisbon, Portugal, represents a tertiary university/public
maternity where no CSs are performed based on maternal request.
We reviewed and analyzed the clinical data from all deliveries that occurred after
IL in this institution in 2015 and 2016. Every pregnant woman was classified according
to the RCS ([Table 1]). We have excluded all women from groups in which either no IL was performed (groups
1 and 3) or if there was a formal indication to perform an elective CS (group 9).
We have also excluded all women that went into spontaneous labor and those submitted
to elective CS.
The IL methods used were: 1) intravenous oxytocin (initial dose of 15 mL/hour with
progressive increase until regular contractility was achieved or until reaching a
maximum dose of 192 mL/hour); 2) intravaginal prostaglandins (vaginal application
of 25 μg misoprostol capsules every 4 hours up to a maximum of 5 applications over
24 hours, or vaginal application of 10 mg prolonged-release pessary of dinoprostone
to be withdrawn in the active stage of labor or after 24 hours); or 3) transcervical
Foley catheter (Foley catheter 16 inserted after vaginal disinfection, inflated with
40 mL of distilled water, and to be withdrawn in the active stage of labor or after
24 hours, either followed or not by intravenous oxytocin or intravaginal prostaglandins).
The IL was considered a failure when no cervical changes were recorded in 48 hours.
A history of previous CS represented a contraindication for IL with misoprostol and
two or more CSs were a formal indication for an elective CS.
We analyzed and compared the CS rates according to each method of IL employed and
each RCS group . Statistical analysis was performed using the chi-squared test on
the IBM SPSS, version 22.0 (IBM Corp. Armonk, NY, USA), and p values < 0.05 were considered statistically significant.
Results
Throughout the period of time considered, 1,166 pregnant patients were submitted to
IL and accounted for 26.9% of all deliveries. The CS rate after IL was 20.9% (n = 244) and represented 23.1% of all CSs performed in 2015 and 2016.
The highest CS rates ([Table 2]) were recorded in groups 5 (65.2%) and 8 (32.3%). The CS rate in group 7 was 20%,
and 20.6% in group 10. Group 2, which represented 56.7% of the study population, was
the one that contributed the most to the overall CS rate, followed by group 5 (65.2%).
Table 2
Cesarean section rate after induction of labor labor according to each group of the
Robson Classification System
|
Groups
|
CS rate[a]
|
Relative size of the group[b]
|
Absolute contribution to the overall CS rate[c]
|
Relative contribution to the overall CS rate[d]
|
|
Group 2
|
22.4 (148/661)
|
56.7 (661/1,166)
|
12.7 (148/1,166)
|
60.7 (148/244)
|
|
Group 4
|
8.3 (27/326)
|
28 (326/1,166)
|
2.3 (27/1,166)
|
11.1 (27/244)
|
|
Group 5
|
65.2 (43/66)
|
5.7 (66/1,166)
|
3.7 (43/1,166)
|
17.6 (43/244)
|
|
Group 6
|
0 (0/4)
|
0.3 (4/1,166)
|
0 (0/1,166)
|
0 (0/244)
|
|
Group 7
|
20 (1/5)
|
0.4 (5/1,166)
|
0.1 (1/1,166)
|
0.4 (1/244)
|
|
Group 8
|
32.3 (10/31)
|
2.7 (31/1,166)
|
0.9 (10/1,166)
|
4.1 (10/244)
|
|
Group 10
|
20.6 (15/73)
|
6.3 (73/1,166)
|
1.3 (15/1,166)
|
6.2 (15/244)
|
|
Total
|
–
|
100 (1,166/1,166)
|
20.9 (244/1,166)
|
100 (244/244)
|
Abbreviations: CS, cesarean section; IL, induction of labor.
a % (number of CS in the group/number of women in the group);
b % (number of women in the group/total number of IL);
c % (number of CS in the group/ total number of IL);
d % (number of CS in the group /total number of CS).
The intravaginal prostaglandins method was the most used for IL (77%), followed by
transcervical Foley catheter (15.9%) and intravenous oxytocin (7.1%) ([Table 3]). When compared with other methods, the transcervical Foley catheter was associated
with a higher CS rate (p = 0.042 and p < 0.001). There was no significant difference between using oxytocin and intravaginal
prostaglandins (p = 0.427). The transcervical Foley catheter was the preferred method in group 5 (74.2%),
while the intravaginal prostaglandins method was the most used in all other groups
(79.6–100%). The CS rate after IL with intravaginal prostaglandins was never > 25.9%.
Table 3
Methods for induction of labor and cesarean section rates according to each group
of the Robson Classification System
|
Groups
|
Transcervical Foley catheter
|
Intravenous oxytocin
|
Intravaginal prostaglandins
|
|
IL[a]
|
CS rate[b]
|
IL[a]
|
CS rate[b]
|
IL[a]
|
CS rate[b]
|
|
Group 2
|
15.6 (103/661)
|
22.3 (23/103)
|
4.8 (32/661)
|
6.3 (2/32)
|
79.6 (526/661)
|
23.4 (123/526)
|
|
Group 4
|
7.1 (23/326)
|
21.7 (5/23)
|
8.6 (28/326)
|
7.1 (2/28)
|
84.4 (275/326)
|
7.3 (20/275)
|
|
Group 5
|
74.2 (49/66)
|
67.4 (33/49)
|
22.7 (15/66)
|
66.7 (10/15)
|
3 (2/66)
|
0 (0/2)
|
|
Group 6
|
0 (0/4)
|
0 (0/0)
|
0 (0/4)
|
0 (0/0)
|
100 (4/4)
|
0 (0/4)
|
|
Group 7
|
0 (0/5)
|
0 (0/0)
|
0 (0/5)
|
0 (0/0)
|
100 (5/5)
|
20 (1/5)
|
|
Group 8
|
3.2 (1/31)
|
100 (1/1)
|
9.7 (3/31)
|
66.7 (2/3)
|
87.1 (27/31)
|
25.9 (7/27)
|
|
Group 10
|
12.3 (9/73)
|
11.1 (1/9)
|
6.9 (5/73)
|
40 (2/5)
|
80.8 (59/73)
|
20.3 (12/59)
|
|
Total
|
15.9 (185/1,166)
|
34.1 (63/185)
|
7.1 (83/1,166)
|
21.7 (18/83)
|
77 (898/1166)
|
18.2 (163/898)
|
Abbreviations: CS, cesarean section; IL, induction of labor.
a % (number of IL in the group with each method/total number of women in the group);
b % (number of CS in the group with each method/number of IL in the group with each
method).
Discussion
Throughout the period of time considered, the IL rate (26.9%) was similar to what
has been reported by other countries.[1] The observed CS rate after IL (20.9%) was lower than the overall CS rate of our
institution and may be explained by the fact that we are a tertiary hospital, capable
of monitoring high-risk pregnancies that often have a formal indication for an elective
CS. The exclusion of elective CSs from our sample may justify, in part, the lower
value of the CS rate observed after the IL. Furthermore, it could also be related
to the meticulous case choice for IL, based on the conviction of a high probability
of a vaginal delivery.
The intravaginal prostaglandins method was the most used method for IL in all groups,
except group 5, in which misoprostol cannot be used. Intravaginal prostaglandins can
be used in different doses, formulations and routes of administration. Despite being
off-label and associated with uterine hyperstimulation, its use according to our protocol
is one of the most effective for IL.[16] When compared with other methods, the IL with misoprostol results in higher rates
of vaginal deliveries and in lower rates of CS, especially when the Bishop score is
not favorable (< 6).[1] Therefore, it is actually the preferred method for IL.
The transcervical Foley catheter was the second most used method for IL (15.9%) and
the one associated with a higher CS rate (34.1%). Since it is linked to a lower risk
of uterine hyperstimulation and it is not contraindicated for IL in women with a previous
CS, it was the preferred method in group 5 (74.2%). In the past, transcervical Foley
catheter was replaced by pharmacological agents, but recently it has showed promising
results, either alone or in combination with other methods, especially when used with
unfavorable Bishop scores.[17]
[18]
[19]
Oxytocin is a commonly used method for IL worldwide, either alone or in combination
with other methods. However, when used alone, it is less effective than intravaginal
prostaglandins.[20] In our institution, we use it in a residual subgroup of women with favorable Bishop
scores. Furthermore, it is also an option for IL in women with a previous CS, which
might explain the CS rate of 21.7%. According to the World Health Organization (WHO),
the use of oxytocin alone for the IL should be reserved for situations when intravaginal
prostaglandins are not available.[1]
As expected, groups 2 and 4 represented 84.7% of our sample. Since group 2 (n = 661) accounted for 56.7% of the entire population, and even with its CS rate of
22.4%, it was the biggest contributor (60.7%) to the overall CS rate. After comparing
these results with the CS rate of 10% recorded in group 1 in our institution since
2014, IL seems to be associated with a higher CS rate. Nevertheless, and according
to Robson,[21] this number continues to be lower than the expected CS rate of 25 to 30% after IL
in this group.
Much like what has been reported by other studies, group 5 revealed the highest CS
rate, even higher than expected.[18]
[19]
[21]
[22] These results are connected to the fear of uterine rupture and to the difficulty
of choosing an IL method that is not contraindicated and, therefore, that is also
less effective.[23]
[24] Despite the small size of this group (n = 66), it was the second biggest contributor (17.6%) to the overall CS rate. With
the progressive increase of CSs performed worldwide, we also expect in the future
a higher number of women and of IL in this group.[25]
[26] In this setting, the use of the transcervical Foley catheter is more effective than
the use of oxytocin alone. However, the heterogeneity of the characteristics of these
women, both clinical and obstetric, interferes with and adds difficulty to the choice
of an ideal method for IL in group 5.
Group 10 (n = 73) was the third largest group (6.3%) of our sample, which might be related to
the characteristics of our neonatal intensive care unit. Despite the fact that the
CS rate tends to be higher with lower gestational ages, the CS rate in this group
(20.6%) was acceptable.[17]
[27]
Group 4 (n = 326) represented 28% of our sample and had a CS rate of 8.3%, higher than the expected
4% to 6%.[21] The comorbidities of this population might have contributed to this number.
Since we represent a national reference in the field of medically assisted procreation,
the IL rate of twin pregnancies is significant (n = 31). Thus, we also have practice in twin vaginal deliveries. Despite the high CS
rate recorded in group 8 (32.3%), it is still lower than what has been recorded in
previous studies.[21]
[28] Because there is a lack of studies regarding the best method for IL in this group,
intravaginal prostaglandins were the most used (87.1%).
In the past few years, the number of cephalic versions and breech vaginal deliveries
performed in our institution has been increasing with encouraging outcomes, which
contributed to the progressive reduction of CS rates in groups 6 and 7.[29]
[30] Nevertheless, the numbers of ILs in these groups are residual, due to the reduction
of training and to the careful selection of cases. However, we have noted a low rate
of CSs in these groups (0% and 20%, respectively).
The retrospective design of our study represents a limitation. Additionally, we did
not evaluate all the demographic and clinical characteristics of our sample, which
makes it a challenge to compare our results to those reported by previous studies.
While we acknowledge the possible difference in effectiveness between using the transcervical
Foley catheter alone or in combination with other methods, we have decided to analyze
this data together, due to the small number of cases.
The RCS allowed for a better comparison between different methods of IL, especially
with regard to their choice in each group. The differences between the CS rates in
each group, as well as a comparison to those reported by previous studies, allow us
to identify target groups for a better approach when IL is considered (group 5).
Although the CS rate after IL was lower than the overall CS rate of our institution
in the considered period of time, we cannot claim that IL is associated with a reduction
in CS rates, given the high number of elective CSs performed.
Conclusion
The number of CSs performed after IL corresponded to 23.1% of the total. The intravaginal
prostaglandins method was the most used and also the most effective. The transcervical
Foley catheter was the method associated with a higher CS rate, probably because it
was the preferred method in group 5. The RCS seems to be useful in this evaluation,
as it simplifies the stratification of the population and the interpretation and comparison
of the results.
