Abstract
Background
Induction of labor has become one of the most common interventions in obstetrics. Induction is indicated when the benefits to either mother or fetus outweigh those of continuing the pregnancy. Maternal complication rates that are increased in association with labor induction include cesarean delivery, chorioamnionitis, abruptio placentae, and uterine atony. So identifying those pregnancies that can be induced with low risk of cesarean delivery is important. The aim of this study was to identify those factors which influence the risk of emergency cesarean delivery in induced labors at term.
Methods
It is a case–control study conducted at Tertiary care center and affiliated hospitals. In this study, odds ratio with 95 % confidence interval is taken as a measure of relative risk. Patients were evaluated for risk factors for cesarean section using logistic regression. Cases include all women who were induced at term and delivered by emergency cesarean section. Controls include all women who were induced at term and delivered vaginally.
Results
The risk factors for cesarean delivery are advanced maternal age at delivery (≥35 years), high early pregnancy body mass index (≥30 kg/m2), nulliparity, low preinduction Bishops score (<5), gestational diabetes mellitus, and intrauterine growth restriction.
Conclusion
Women with multiple risk factors for cesarean can be taken up for elective cesarean section rather than inducing them at term.
Keywords: Induction of labor, Cesarean delivery, Risk factors
Introduction
The history of labor induction dates back to the time of Hippocrates’ original descriptions in which mammary stimulation and mechanical dilation of the cervical canal are used methods of induction [1]. Induction implies stimulation of contractions before the spontaneous onset of labor, with or without ruptured membranes. Augmentation refers to stimulation of spontaneous contractions that are considered inadequate. Induction is indicated when the benefits to either mother or fetus outweigh those of continuing the pregnancy. Common indications include gestational hypertension, premature rupture of membranes, non-reassuring fetal status, postterm pregnancy, intrauterine growth restriction, and various maternal medical conditions such as chronic hypertension and diabetes.
Induction of labor has been associated with a risk of emergency cesarean delivery. The decision to induce a delivery in less imminent situation is often difficult. If induction fails, an emergency cesarean delivery has to be performed, and maternal risks are greater in emergency cesarean delivery than those in elective cesarean deliveries. So, the aim of this study was to identify those pregnancies which are associated with greater risk of cesarean delivery when induced at term.
Materials and Methods
Study Design
This is a case–control study in which odds ratio (OR) with 95 % confidence interval (CI) is used as a measure of relative risk.
Place of Study
Tertiary care center and affiliated hospitals.
Duration of Study
From June 2010 to December 2011.
Statistical Analysis
All comparisons are estimated and expressed as OR with 95 % CI. Using logistic regression analysis, all comparisons were estimated and were expressed as OR with 95 % CI. The data were modeled through multiple logistic regressions, and adjustments were made for independent variables that had a significant influence on the risk of cesarean delivery in the univariate analysis. The data analysis was performed using IBM®SPSS®Statisticsversion 18 software and Hosmer and Lemeshow Test.
Study Population
The cohort included all women with a live singleton fetus in the cephalic position and induced at term (≥37 weeks). Cases were women who delivered by emergency cesarean section and controls were women with a vaginal delivery among the cohort. A total of 277 women were studied, out of which 117 women delivered by emergency cesarean section and 160 women delivered vaginally.
Data Collection
Information of women induced was obtained from case records and antenatal cards.
Definition of Variables
Maternal age was defined as age in completed years at delivery and divided into two categories (Age ≥35 years and age <35 years). Parity is defined as the number of previous pregnancies crossed age of viability (≥28 weeks). Maternal weight was taken in kilograms (Kgs) and height in meter (M) in early pregnancy (10–14 weeks), and body mass index (BMI) was calculated using the formula: Weight in Kgs/Height in M square. BMI was categorized into two groups (BMI ≤30 and BMI >30). Preinduction Bishops score was calculated [2]. Indications such as postterm pregnancy, gestational diabetes mellitus (GDM), hypertensive disorders in pregnancy, intrauterine growth restriction (IUGR), and premature rupture of membranes (PROM) for induction were taken into account. Epidural analgesia if used was noted. Emergency cesarean is defined as a cesarean delivery after failed induction, failed progress of labor, fetal asphyxia, or due to other intrapartum maternal or fetal complication.
Method of Induction
All women enrolled were examined prior to induction and induced using Dinoprostone gel (0.5 mg) intracervically (doses may be repeated after 6 h, with a maximum of two doses in 24 h) and if required, labor was augmented using oxytocin (starting dose of 6 mU/min, with 6 mU/min increase every 40 min, but employs flexible dosing based on uterine response).
Exclusion Criteria
The exclusion criteria include previous cesarean section, uterine scar (myomectomy), multifetalgestation, malpresentation, and where vaginal delivery was otherwise contraindicated.
Results
Using logistic regression analysis, all comparisons are estimated and expressed as OR with 95 % CI. Factors associated with cesarean delivery are analyzed (Table 1). Multivariate logistic regression of factors for cesarean delivery (Table 2).
Table 1.
Analysis of risk factors for cesarean delivery
| Sr. no. | Risk factors | Cesarean delivery (N = 117) no (%) |
Vaginal delivery (N = 160) no (%) |
Crude odds ratio (95 % CI) |
|---|---|---|---|---|
| 1. | Maternal age | |||
| <35 years | 107 (91.46) | 158 (98.75) | 7.383 (1.586–34.367) | |
| ≥35 years | 10 (8.54) | 2 (1.25) | ||
| 2. | Body mass index (Kg/M2) | |||
| ≤30 | 79 (67.52) | 148 (92.5) | 5.93 (2.934–11.996) | |
| >30 | 38 (32.48) | 12 (7.5) | ||
| 3. | Parity | |||
| Nullipara (0) | 105 (89.75) | 98 (61.25) | 0.181 (0.092–0.355) | |
| Multipara (≥1) | 12 (10.25) | 62 (38.75) | ||
| 4. | Bishops score | |||
| <5 | 78 (33.3) | 73 (54.4) | 0.4195 (0.2559–0.6879) | |
| ≥5 | 39 (66.7) | 87 (45.6) | ||
| 5. | Epidural analgesia | |||
| No | 79 (32.5) | 113 (29.4) | 1.1565 (0.6908–1.9360) | |
| Yes | 38 (67.5) | 47 (70.6) | ||
| 6. | Hypertensive disorders in pregnancy | |||
| Yes | 32 (27.4) | 49 (30.6) | 0.8528 (0.5032–1.4453) | |
| No | 85 (72.6) | 111 (69.4) | ||
| 7. | Gestational diabetes mellitus | |||
| Yes | 27 (23.1) | 21 (13.1) | 1.9857 (1.0587–3.7244) | |
| No | 90 (76.9) | 139 (86.9) | ||
| 8. | Postterm pregnancy | |||
| Yes | 36 (30.8) | 48 (30) | 1.0370 (0.6177–1.7411) | |
| No | 81 (69.2) | 112 (70) | ||
| 9. | IUGR | |||
| Yes | 1 (0.9) | 15 (9.4) | 0.0833 (0.0108–0.6402) | |
| No | 116 (99.1) | 145 (90.6) | ||
| 10. | PROM | |||
| Yes | 23 (19.7) | 24 (15) | 1.3865 (0.7389–2.6019) | |
| No | 94 (80.3) | 136 (85) | ||
IUGR intrauterine growth restriction, PROM premature rupture of membranes, CI confidence interval
Statistically significant data is marked in bold
Table 2.
Multivariate analysis of risk factors for cesarean delivery
| Sr no. | Risk factors | Adjusted odds ratio (95 % CI) | Sig. |
|---|---|---|---|
| 1 | Maternal age | 8.683 | 0.003 |
| 2 | Body mass index | 28.505 | 0.000 |
| 3 | Nulliparity | 28.025 | 0.000 |
| 4 | Bishops score | 12.067 | 0.001 |
| 5 | Epidural analgesia | 0.306 | 0.580 |
| 6 | Hypertensive disorders in pregnancy | 0.350 | 0.554 |
| 7 | Gestational diabetes mellitus | 4.672 | 0.031 |
| 8 | Postterm pregnancy | 0.019 | 0.891 |
| 9 | IUGR | 9.014 | 0.003 |
| 10 | PROM | 1.041 | 0.308 |
IUGR intrauterine growth restriction, PROM premature rupture of membranes, CI confidence interval
Statistically significant data is marked in bold
Our study had shown that maternal age ≥35 years, BMI ≥30 kg/m2, nulliparity, preinduction Bishops score less than 5, gestational diabetes mellitus, and intrauterine growth restriction are significantly associated with cesarean delivery. The presence of epidural analgesia, gestational hypertension, postterm pregnancy, and premature rupture of membranes is not associated with significant increase in cesarean delivery if labor is induced at term.
Discussion
Though advanced maternal age is not significantly associated with cesarean delivery in a study by Cnattingius et al. [3], a systematic review by Bayrampour et al. [4] has shown that there is an independent association between advanced maternal age and cesarean delivery. Our study has shown significant association of advanced maternal age with cesarean delivery in induced labors.
Poobalan et al. [5] did a systematic review on the effect of BMI in nulliparous women on mode of delivery. They concluded that cesarean delivery risk is increased by 50 % in overweight women (BMI 25–30 kg/m2), and is more than double for obese women (BMI 30–35 kg/m2) compared with women with normal BMI (20–25 kg/m2).
Study by Sheiner et al. [6] and Ehrenberg et al. [7] also showed significant association between obesity and cesarean delivery even after the exclusion of hypertensive disorders and diabetes mellitus. Our study also has shown significant association between high BMI (>30 kg/m2) and cesarean delivery.
A study by Cnattingius et al. [3], which resembles closest to our study has shown that the risk of cesarean delivery was increased among nulliparous. Similar association is seen between nulliparity and cesarean delivery in study by Ehrenberg et al. [7]. Our study also showed significant association between nulliparity and cesarean delivery.
As far as role of preinduction Bishops score is concerned, our study has showed significant association between low preinduction Bishops score (<5) and cesarean delivery. Similar results were seen in study by Johnson et al. [8].
Study by Ehrenberg et al. [7] and Rosenberg et al. [9] has shown significant association between cesarean delivery and pregestational as well as gestational diabetes mellitus. Our study has concluded the same results.
In our study, epidural analgesia is not significantly associated with cesarean delivery. Similar results are seen in study by Cnattingius et al. [3]. A study by Cynthia et al. [10] has also concluded that neuraxial analgesia in early labor did not increase the rate of cesarean delivery, and in fact it provides better analgesia and resulted in a shorter duration of labor than systemic analgesia.
Though study by Zhang et al. [11] showed that more than half of women with preeclampsia and eclampsia had cesarean delivery, our study did not show a significant association between hypertensive disorders of pregnancy and cesarean delivery. A multicentre, open-label-randomized-controlled trial by Koopmans et al. [12] has recommended that induction of labor is associated with improved maternal outcome and should be advised for women with mild hypertensive disease beyond 37-weeks’ gestation.
In our study, postterm pregnancy is not significantly associated with cesarean delivery. Similar results were seen in a study by Sanchez-Ramos et al. [13]. They recommended that labor induction at 41-weeks’ gestation for otherwise an uncomplicated singleton pregnancy reduces cesarean delivery rates without compromising perinatal outcomes.
Our study has shown that IUGR and cesarean deliveries are significantly associated. However, K E Boers and associates [14] have shown that there is no increase in operative and instrumental delivery rates in induced labors in pregnancies complicated by IUGR.
In our study, pregnancies with PROM and induction of labor are not significantly associated with cesarean deliveries. Induction of labor in such cases reduces risk of maternal infections. Systematic review by Dare et al. [15] concluded the same results.
A vaginal delivery is the best choice for both mother and child. However, it is better to take those patients with multiple risk factors for elective cesarean section rather than inducing them at term. Our study does not have sufficient power to evaluate the combined effect of several risk factors for cesarean delivery when labor is induced at term and further evaluation is needed for this.
Acknowledgments
Conflict of interest
None.
Ethical Statement
Study was approved by ethical committee of Armed Forces Medical College, Pune.
Nilesh Mhaske
is currently serving as a Graded Specialist in Obstetrics and Gynaecology at Military Hospital, Gopalpur. He has completed MBBS from Dr VM Government Medical College, Solapur, in December 2005. As he was passionate to join the Indian Armed Forces, he joined Army Medical Corps immediately after completing his internship. After serving in Jammu and Kashmir and United Nations peace keeping forces (Sudan), he took Gynaecology and Obstetrics as a speciality for his postgraduation. He completed his postgraduation (MS) in July 2013 from the prestigious Armed Forces Medical College, Pune, and posted to this hospital. His areas of interest are high risk obstetrics and endoscopic surgery. Apart from his profession, he likes adventurous activities such as parajumping, mountaineering, and photography
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