- Email: [email protected]
The Edmonton Obesity Staging System Predicts Mode of Delivery After Labour Induction
OBSTETRICS
The Edmonton Obesity Staging System Predicts Mode of Delivery After Labour Induction Ashley Nicole Demsky, MD, MSc;1 Shawna Marie Stafford, MD, MSc;1 Daniel Birch, MD, MSc;2 Arya M. Sharma, MD;3 Jane Ann Schulz, MD;1 Helen Steed, MD1 1
Department of Obstetrics and Gynecology, Lois Hole Hospital for Women, University of Alberta, Edmonton, AB
2
Department of Surgery and Center for the Advancement of Minimally Invasive Surgery, Royal Alexandra Hospital, University of Alberta, Edmonton, AB 3
Department of Medicine, University of Alberta, Edmonton, AB
A.N. Demsky
Abstract Objective: This study sought to evaluate the use of the Edmonton Obesity Staging System (EOSS) in predicting Caesarean delivery among term, nulliparous, and singleton pregnancies in women with overweight or obesity who are undergoing an induction of labour. Methods: A prospective cohort study was performed in Edmonton, Alberta. Women undergoing an induction of labour at term were recruited to either a sample cohort, including women with a body mass index of ≥25.0 kg/m2 at first antenatal visit, or a control cohort with a body mass index of 18.5 to 24.9 kg/m2. Participating women provided a self-reported health history and consented to review of their medical records allowing allocation into EOSS categories. The primary outcome was the rate of Caesarean delivery based on EOSS category. Secondary outcomes consisted of a summary score of adverse maternal, delivery, and neonatal events (Canadian Task Force Classification II-2). Results: Overall, 345 women were recruited, with a participation rate of 93.7%. The sample cohort consisted of 276 women with overweight or obesity, whereas the control cohort included 69 normal-weight women. The overall rate of Caesarean delivery was 30.4% for the control cohort and 35.8%, 29.9%, 43.2%, and 90.5% for women assigned an EOSS category 0, 1, 2, and 3, respectively (P < 0.001). A summary score was not indicative of overall rate of adverse maternal, delivery, and neonatal events (P = 0.22). Conclusion: The EOSS may help predict the chance of Caesarean delivery in a high-risk group of nulliparous women with Key Words: Obesity, labour induction, body mass index (BMI), Edmonton Obesity Staging System (EOSS), Caesarean delivery Corresponding author: Dr. Ashley Nicole Demsky, Department of Obstetrics and Gynecology, Lois Hole Hospital for Women, University of Alberta, Edmonton, AB. [email protected] Competing interests: See Acknowledgements. Each author has indicated that they meet the journal’s requirements for authorship. Received on February 19, 2019 Accepted on August 15, 2019
overweight or obesity who are undergoing an induction of labour at term.
Résumé tude visait a e valuer l’utilisation du syste me de Objectif : Cette e site EOSS (Edmonton Obesity Staging classification de l’obe dire la probabilite d’un accouchement par System) pour pre sarienne en cas de de clenchement artificiel du travail d’une ce terme chez une femme nullipare en grossesse monofœtale a site . surpoids ou atteinte d’obe tude de cohorte prospective a e te re alise e a Méthodologie : Une e des femmes Edmonton en Alberta. Les chercheurs ont recrute clenchement artificiel du travail d’une grossesse devant subir un de terme et les ont re parties en deux groupes : soit dans un groupea chantillon de femmes ayant un indice de masse corporelle de 25,0 e re consultation de suivi pre natal, soit kg/m2 ou plus lors de la premie moin de femmes ayant un indice de masse dans un groupe te 24,9 kg/m2. Les participantes ont autode clare corporelle de 18,5 a ce dents me dicaux et consenti a l’examen de leur dossier leurs ante dical aux fins de classification en fonction des cate gories de me sariennes fonde sur la classification de l’EOSS. Le taux de ce re de jugement principal. Les crite res de l’EOSS constituait le crite jugement secondaires consistaient en un indice global des ve nements de favorables maternels, obste tricaux et ne onataux e tude canadien sur les soins de (classification II-2 du Groupe d’e pre ventifs). sante te recrute es pour cette e tude, Résultats : Un total de 345 femmes ont e sente un taux de participation de 93,7 %. Le groupelaquelle pre chantillon se compose de 276 femmes en surpoids ou atteintes e site , tandis que le groupe te moin comprend 69 femmes de d’obe sariennes global est de 30,4 % pour les poids normal. Le taux de ce moin et de 35,8 %, 29,9 %, 43,2 % et 90,5 % femmes du groupe te es dans les cate gories 0, 1, respectivement pour les femmes classe re 2 et 3 selon l’EOSS (P < 0,001). Un indice global ne s’est pas ave ve lateur du taux global d’e ve nements de favorables maternels, re tricaux et ne onataux (P = 0,22). obste pre dire la probabilite Conclusion : L’EOSS pourrait aider a sarienne dans un groupe a risque e leve de d’accouchement par ce site en cas de femmes nullipares en surpoids ou atteintes d’obe clenchement artificiel du travail d’une grossesse a terme. de
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© 2019 The Society of Obstetricians and Gynaecologists of Canada/La Société des obstétriciens et gynécologues du Canada. Published by Elsevier Inc. All rights reserved.
J Obstet Gynaecol Can 2019;000(000):1−9 https://doi.org/10.1016/j.jogc.2019.08.022
INTRODUCTION
besity has become the most prevalent chronic disease affecting women of reproductive age. Approximately 20% of Canadian women aged 18 to 34 have obesity.1 With over 380 000 births in Canada per year, an estimated 76 000 are therefore affected by this condition.2 Excess maternal weight is associated with adverse events in pregnancy, including increased rates of hypertensive disorders, gestational diabetes, abnormal labour patterns, and, most importantly, obstetrical interventions such as Caesarean delivery.3−7 The risks of stillbirth and fetal death are also augmented.8 Furthermore, high body mass index (BMI) is associated with an increased need for an induction of labour as a result of both complications related to pregnancy and prolonged gestations.9,10 This intervention compounds delivery-related risk for women with obesity because women whose labour is induced are more likely to undergo an emergency Caesarean delivery.10 An emergency Caesarean delivery after a failed induction of labour carries a higher rate of complications than a vaginal delivery or elective Caesarean delivery.11 As such, prevention of emergency Caesarean delivery is instrumental in reducing morbidity for women with obesity in pregnancy.
O
Historically, BMI has been used to stratify obesity-related risk for women at term. Traditional thinking is that as BMI increases, so does the risk of adverse outcomes, including Caesarean delivery. Not all women, however, are equally affected by obesity. For example, two women with a BMI of 35 kg/m2 may be affected differently: One woman may have no obesity-related comorbidities, and the second may have a history of depression, gestational diabetes, and gallbladder disease. Excess weight will affect the global health status of the second patient to a greater degree. BMI alone fails to convey these differences and cannot accurately predict which patient is at higher risk of Caesarean delivery. Accurate prediction of Caesarean delivery would be useful for care providers. Should risk of emergency Caesarean delivery be excessive and chance of low-risk vaginal delivery be minimal, planning for elective Caesarean delivery could help mitigate risks associated with emergency surgery. A more accurate approach to delineate which women will be at highest risk for Caesarean delivery is needed. The
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Edmonton Obesity Staging System (EOSS) has been proposed as a method of determining outcomes in patients with increased weight that is superior to BMI alone.12 The EOSS is a clinical staging system that individualizes risk profiles by incorporating knowledge of a patient’s current health status and weight-related comorbidities. To date, the EOSS has been more successful than BMI at predicting long-term mortality rates, poor postoperative outcomes in non-obstetrical patients, and pregnancy rates in women undergoing fertility treatments.13−16 It has not yet been applied to obstetrical populations. This study aimed to explore the use of the EOSS to predict mode of delivery among women with overweight or obesity who are undergoing an induction of labour. Women who are more affected by obesity-related comorbidities may be at higher risk of Caesarean delivery. We hypothesized that parturients at higher EOSS categories would have an increased rate of Caesarean delivery. METHODS
A prospective cohort study was performed at two highvolume obstetrical centers in Edmonton, Alberta. The Lois Hole Hospital for Women is a tertiary referral center, and the Grey Nuns Hospital is a community hospital. Both perform over 7000 deliveries per annum. Ethical approval was obtained from the Human Research Ethics Board at the University of Alberta (Pro00075527) before commencement of the study. Recruitment was done simultaneously at each site between January 2018 and August 2018. Women scheduled for an induction of labour were screened daily by nursing staff for possible inclusion in the study. Researchers were then contacted for recruitment. All initiated inductions in nulliparous women ≥18 years old at ≥370 gestational age with singleton, vertex pregnancies and documented prenatal care were included. Nulliparity was defined as no previous deliveries ≥20 weeks gestational age. Exclusion criteria included a previous myomectomy, BMI <18.5 kg/m2, midwifery care, presentation for a planned assisted second stage, the presence of congenital fetal anomalies or predetermined fatal fetal outcomes, no prenatal care, and non −English-speaking women. To limit bias, researchers were not involved in patient care; if a researcher provided emergency care, that participant was removed from the study. At recruitment, participants provided written consent. Participants were asked to complete a personal health history. They also consented to a full review of their medical records, including their prenatal, delivery, and current
The Edmonton Obesity Staging System Predicts Mode of Delivery After Labour Induction
Table 1. Edmonton Obesity Staging System Category
Classification
Common disease examples
0
No apparent risk factors
No apparent obesity-related risk factors No physical symptoms No psychopathology No functional limitations No impairment of well-being
1
Subclinical risk factors associated with obesity
Borderline hypertension not requiring medical therapy Impaired glucose tolerance, self-reported or abnormal gestational diabetes screen History of irregular menses of unknown cause Mild physical symptoms related to obesity Mild psychopathology Mild impairment in well-being
2
Established obesity-related chronic disease
Essential or gestational hypertension Gestational diabetes Type 2 diabetes Polycystic ovarian syndrome Use of assisted reproductive technology Dyslipidemia Non-alcoholic fatty liver disease Known gallstones or prior cholecystectomy Osteoarthritis Obstructive sleep apnea Incontinence before pregnancy Moderate psychopathology (depression, anxiety, disordered eating behavior, significant body image disturbance) Moderate impairment of well-being
3
Established obesity-related chronic disease with end-organ damage
Preeclampsia Stroke Myocardial infarction Angina Heart failure Diabetic complications Thromboembolic disease Hepatic dysfunction or hematoma Pulmonary edema Renal insufficiency Incapacitating osteoarthritis Significant impairment of well-being
4
Severe (potentially end-stage) disabilities from obesity-related chronic diseases
Eclampsia Dialysis Bedridden or unable to mobilize Disabling psychopathology and/or severe impairment of well-being
Adapted from Sharma and Kushner.12
hospital admission records. Research participants were stratified into two groups according to their measured weight at their first antenatal visit. The sample cohort consisted of women with a BMI ≥25.0 kg/m2, and the control cohort consisted of normal-weight women with a BMI of 18.5 to 24.9 kg/m2. There were no interventions or alterations to patient care. After enrolment and before delivery, two researchers independently assigned women in the sample cohort to an EOSS category on the basis of their obesity-related comorbidities. The EOSS used in this study has been modified for use in pregnancy by incorporating pregnancy-related
complications that have been previously associated with obesity, such as gestational diabetes and hypertensive disorders of pregnancy (Table 1). Its creator (A.M.S.) reviewed the modified version of this scale for face validity. In patients with multiple comorbidities, the most severe comorbidity determined the EOSS category. Data were entered into REDCap, a secure platform for data storage supported by the University of Alberta. At the conclusion of the study, all records were reviewed for accuracy. Maternal demographics, maternal comorbidities, and labour information were evaluated (Tables 2 and 3).
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Table 2. Maternal characteristics Characteristics
Control n= 69
EOSS 0 n = 53
EOSS 1 n = 77
EOSS 2 n = 125
EOSS 3 n = 21
Demographics Age (years), median (IQR) Smoker, n (%)
30.0 (27.0−32.0) 29.0 (26.0−31.0) 29.0 (25.0−31.0) 30.0 (28.0−33.0) 31.0 (27.0−34.0) 3 (4.3)
0 (0)
7 (9.1)
11 (8.8)
3 (14.3)
Gestational age (weeks and days), median (IQR) Delivery
41.0 (39.6−41.1) 41.1 (40.1−41.3) 41.0 (39.6−41.3) 39.3 (39.1−40.3) 38.3 (37.6−39.3)
First antenatal visit
17.0 (14.4−19.6) 21.6 (16.6−27.0) 21.0 (16.1−24.6) 18.9 (13.0−23.6) 18.1 (13.7−24.7)
BMI, median (IQR) Delivery
27.0 (25.9−28.4) 32.7 (30.6−37.2) 33.4 (30.9−37.6) 35.2 (32.0−41.1) 37.5 (32.8−45.1)
First antenatal visit
22.4 (21.3−23.4) 28.5 (26.6−31.9) 29.1 (26.8−33.2) 31.7 (28.4−38.4) 33.5 (30.4−41.1)
GWG (kg), median (IQR)
13.5 (9.9−16.7)
9.0 (5.7−13.6)
9.7 (6.9−12.8)
10.7 (6.3−12.0)
11.6 (6.8−14.5)
Prostaglandin only
47 (68.1)
35 (66.0)
51 (66.2)
90 (72.0)
9 (42.9)
Oxytocin
15 (21.7)
8 (15.1)
17 (22.1)
14 (11.2)
3 (14.3)
Foley catheter only
2 (2.9)
3 (5.7)
5 (6.5)
4 (3.2)
3 (14.3)
Combineda
3 (4.3)
3 (5.7)
2 (2.6)
8 (6.4)
2 (9.5)
b
2 (2.9)
3 (5.7)
2 (2.6)
2 (9.5)
4 (19.0)
0 (0)
1 (1.9)
0 (0)
0 (0)
0 (0)
Primary mode of induction, n (%)
Sequential ARM
Cervical dilation at admission (cm), median (IQR)
2.5 (1.5−3.0)
2.0 (1.0−3.0)
3.0 (1.5−3.0)
3.0 (1.5−3.0)
1.0 (0.0−2.0)
GBS positive, n (%)
11 (15.9)
9 (17.0)
11 (14.3)
27 (21.6)
5 (23.8)
Epidural use, n (%)
59 (85.5)
42 (79.2)
68 (88.3)
108 (86.4)
14 (66.7)
Received ARM, n (%)
46 (66.7)
25 (47.2)
51 (66.2)
81 (64.8)
14 (66.7)
Received oxytocin, n (%)
53 (76.8)
44 (83.0)
66 (85.7)
108 (86.4)
20 (95.2)
Birth weight (g), median (IQR)
3370 (3110−3550)
a
Combined, Foley catheter induction with simultaneous prostaglandin insertion.
b
Sequential, Foley catheter induction after a trial of prostaglandin induction.
3590 (3280−3880)
3580 (3230−3910)
3450 (3140−3710)
3300 (2830−3570)
ARM: artificial rupture of membranes; BMI: body mass index; EOSS: Edmonton Obesity Staging System; GWG: gestational weight gain; IQR: interquartile range.
Variables were recorded from a combination of selfreported data or as documented on hospital records.
admission to the neonatal intensive care unit, maternal death, thromboembolic disease, and mode of delivery.
The primary outcome was rate of Caesarean delivery. The secondary outcome consisted of a summary score of maternal, delivery, and neonatal outcomes. This included the incidence of excessive gestational weight gain, according to the Society of Obstetricians and Gynaecologists of Canada recommended weight gain guidelines (BMI 18.5− 24.9 kg/m2, >16.0 kg; BMI 25.0−29.9 kg/m2, >11.5 kg; BMI ≥30.0 kg/m2, >7.0 kg),17 polyhydramnios or oligohydramnios, chorioamnionitis, abruption, shoulder dystocia, severe perineal tear (≥third-degree tear or episiotomy), manual removal of placenta, excessive blood loss (estimated blood loss >500 mL in vaginal delivery or >1000 mL in Caesarean delivery), blood transfusion, meconium, low Apgar score (≤7 at 1 and 5 minutes), stillbirth after initiation of induction, abnormal birth weight (<2500g or ≥4000g),
The sample size calculation is based on predicted proportion of Caesarean section rate for each category. We anticipated that the emergency Caesarean delivery rate of normal-weight control subjects, after an induction of labour, would be approximately 20%.18 With each increase in EOSS category, there should be an increase in Caesarean delivery rate. Calculations were based on the estimate that the Caesarean delivery rate in the EOSS category 0, 1, 2, and 3 would approach 30%, 35%, 40%, and 45%, respectively. EOSS stage 4 was excluded from our sample size calculation because the presentation of individuals with this degree of illness was unlikely to be encountered. This resulted in a sample size calculation of 345 patients, including EOSS stages 0 to 3 and a group of normal-weight control subjects. Overall, this sample size of 345 achieves 80%
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The Edmonton Obesity Staging System Predicts Mode of Delivery After Labour Induction
Table 3. Summary score and secondary outcomes by Edmonton Obesity Staging System category Control n = 69
EOSS 0 n = 53
EOSS 1 n = 77
EOSS 2 n = 125
EOSS 3 n = 21
1.83 § 1.26
2.02 § 1.28
2.06 § 1.37
2.13 § 1.36
2.62 § 1.66
21 (30.4)
26 (49.1)
41 (53.2)
63 (50.4)
14 (66.7)
Outcome Summary score (P = 0.22) Excessive GWG Abnormal fluid level
2 (2.9)
1 (1.9)
3 (3.9)
4 (3.2)
1 (4.8)
Chorioamnionitis
1 (1.4)
4 (7.5)
6 (7.8)
11 (8.8)
1 (4.8)
Abruption
1 (1.4)
0 (0)
2 (2.6)
3 (2.4)
0 (0)
0 (0)
2 (3.8)
6 (7.8)
6 (4.8)
0 (0)
Severe perineal tear
19 (27.5)
14 (25.4)
12 (15.6)
22 (17.6)
0 (0)
Manual removal of placenta
7 (10.1)
1 (1.9)
2 (2.6)
6 (4.8)
0 (0)
Excessive blood loss
5 (7.2)
10 (18.9)
12 (15.6)
21 (16.8)
5 (23.8)
Blood transfusion
1 (1.4)
0 (0)
0 (0)
0 (0)
1 (4.8)
15 (21.7)
11 (20.8)
18 (23.4)
22 (17.6)
4 (19.0)
8 (11.6)
2 (3.8)
4 (5.2)
9 (7.2)
3 (14.3)
0 (0)
0 (0)
0 (0)
1 (0.8)
0 (0)
Abnormal birth weight
6 (8.7)
7 (13.2)
17 (22.1)
18 (14.4)
3 (14.3)
Admission to NICU
1 (1.4)
1 (1.9)
2 (2.6)
7 (5.6)
2 (9.5)
Shoulder dystocia
Meconium Low Apgar scores Stillbirth
Maternal death
0 (0)
0 (0)
0 (0)
0 (0)
0 (0)
Thromboembolic disease
0 (0)
0 (0)
0 (0)
0 (0)
1 (4.8)
Instrumental delivery
Caesarean delivery
18 (26.1)a -Forceps, 13 (72.2) -Vacuum, 6 (33.3) 21 (30.4)
9 (17.0) -Forceps, 8 (88.9) -Vacuum, 1 (11.1) 19 (35.8)
a
Includes one combined vacuum and forceps.
b
Includes a failed instrumental delivery resulting in a Caesarean delivery.
11 (14.3) -Forceps, 11 (100) -Vacuum, 0 (0) 23 (29.9)
18 (14.4) -Forceps, 16 (88.9) -Vacuum, (11.1) 54 (43.2)
1 (4.8)b -Forceps, 0 -Vacuum, 1 (100) 19 (90.5)
NICU: neonatal intensive care unit; EOSS: Edmonton Obesity Staging System; GWG: gestational weight gain. Data are presented as mean § SD or n (%).
power using the 4 degrees of freedom chi-square test with a significance level (alpha) of 0.05. For the primary outcome, Pearson chi-square tests were used to detect differences among groups with categorical variables. Binomial logistic regression was performed to ascertain odds ratios (ORs). For the secondary outcome, a one-way analysis of variance was conducted to determine whether differences in mean summary scores existed. For all analyses, a statistical difference was taken at a P ≤ 0.05 level of significance. In instances where pairwise comparisons were performed, the type I error was adjusted for multiplicity using Bonferroni correction, and a P value of ≤0.05 remained statistically significant. All statistical analyses were performed using SAS software version 9.4 (SAS Institute Inc., Cary, NC). RESULTS
Overall, 397 patients were approached for recruitment into the study from January 2018 to August 2018 (Figure 1).
Twenty-five women declined to participate, thus yielding an overall participation rate of 93.7%. An additional 27 women were excluded (Figure 1). A total of 154 (55.8%) women from the sample cohort and 36 (52.2%) women from the control cohort were recruited from the tertiary care center, with the remainder derived from the community hospital. Maternal demographics and group characteristic information is presented in Table 2. The control cohort consisted of a total of 69 (20%) women. The sample cohort consisted of 53 (15.4%), 77 (22.3%), 125 (36.2%), and 21 (6.1%) women distributed by EOSS category 0, 1, 2, and 3, respectively. Distribution of the sample cohort by BMI class at first antenatal visit resulted in 129 (39.5%) classified as having overweight (BMI 25.0−29.9 kg/m2) and 147 (42.6%) classified as having obesity (BMI ≥30.0 kg/m2). If further divided by obesity class, there were 74 (50.3%), 39 (26.5%), and 34 (23.1%) in class I (BMI 30.0−34.9 kg/m2), II (BMI 35.0−39.9 kg/m2), and III (BMI ≥40.0 kg/m2), respectively.
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Figure 1. Study cohort selection flow chart.
Figure 2. Rate of Caesarean delivery by Edmonton Obesity Staging System (EOSS) category (P < 0.001).
The rate of Caesarean delivery by EOSS category is presented in Figure 2. Baseline rate of Caesarean delivery for the control cohort was 30.4%. When stratified by EOSS category, 35.8%, 29.9%, 43.2%, and 90.5% of women underwent Caesarean delivery in EOSS category 0, 1, 2, and 3, respectively (P < 0.001). Pairwise comparisons and binomial logistic regression were performed to ascertain the effect of EOSS category on Caesarean delivery. In unadjusted analysis there was no difference in EOSS category 0 (OR 1.3; 95% confidence interval [CI] 0.6−2.7; P = 0.53), EOSS Category 1 (OR 0.97; 95% CI 0.5−2.0; P = 0.94), and EOSS category 2 (OR 1.7; 95% CI 0.9−3.2; P = 0.08). There was significance for EOSS category 3 (OR 21.7; 95% CI 4.6−101.8; P < 0.001). There was no
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statistically significant difference when the model was adjusted by age (P = 0.07) or mode of induction (P = 0.44). Artificial rupture of membranes as a primary mode of induction was not included in the analysis because of the low frequency of occurrence. The rate of Caesarean delivery was also reviewed after excluding all women with a self-reported BMI <25.0 kg/m2 to assess whether any significant misclassification may have altered the described outcomes. This yielded 210 patients, and overall Caesarean delivery rates showed a similar trend, with the highest rate of Caesarean delivery in EOSS category 3 (EOSS 0, n = 14 [40.0%]; EOSS 1, n = 13 [25.0%]; EOSS 2, n = 46 [44.2%]; EOSS 3, n = 17 [89.5%]; P < 0.001). The most common indication for Caesarean delivery was fetal heart rate abnormalities; this was the same for each patient category (control, 42.9%; EOSS 0, 47.3%; EOSS 1, 60.9%; EOSS 2, 57.4%; EOSS 3, 47.4%). Failure to progress in the first stage of labour was the second most common indication (control, 38.1%; EOSS 0, 31.6%; EOSS 1, 39.1%; EOSS 2, 38.9%; EOSS 3, 31.6%). Multiple indications for Caesarean delivery were sometimes provided. Rates of Caesarean delivery were then compared by BMI. Overall rate of Caesarean delivery was 39.5%, 40.5%, 43.6%, and 50.0% for overweight, obesity class I, class II, and class III, respectively. The difference in proportion of Caesarean delivery between weight classes did not reach statistical significance (P = 0.37).
The Edmonton Obesity Staging System Predicts Mode of Delivery After Labour Induction
Finally, secondary outcomes were analyzed using a summary score of adverse maternal, delivery, and neonatal events (Table 3). There was one perinatal death in this study, in an EOSS category 2 participant. The patient was known to have poorly controlled gestational diabetes. She received an induction of labour with prostaglandins that was subsequently complicated by uterine tachysystole. After removal of the prostaglandin and resolution of the tachysystole, she refused further intervention and left against medical advice. After 1 week she presented again for induction with an unexplained fetal death. DISCUSSION
Obesity in pregnancy presents an ongoing challenge for maternity care providers. Our study is consistent with previous reports that determined higher rates of Caesarean delivery in women with overweight and obesity when compared with normal-weight women.18,19 Despite this, there was no statistically significant impact of BMI class on mode of delivery. Therefore, BMI stratification provides no significant predictive utility and is not clinically powerful enough to guide recommendations for mode of delivery. In contrast, the EOSS more clearly delineates a subpopulation of women who are at a high risk of Caesarean delivery. When the EOSS is applied, the rate of Caesarean delivery in the high-risk subpopulation (EOSS category 3) is over 90%. Moreover, Caesarean delivery rates in the EOSS 0 and 1 categories were no higher than in the control populations despite a markedly higher BMI than in control subjects. Given that emergency Caesarean delivery carries the highest complication rate, and that women classed as an EOSS category 3 are at over a 90% risk of this outcome, interventions should be focused at preventing or reducing the morbidity in EOSS category 3 women. Should EOSS category 3 classification persist in pregnancy, patients may be offered an elective Caesarean delivery instead of an induction of labour. This may avoid the morbidity associated with emergency Caesarean delivery, allow for improved resource planning, and spare women from an induction process with a >90% chance of failure. The EOSS may be better able to predict Caesarean delivery at the higher EOSS category because it identifies those women who have been most affected by excess adiposity. Some hypotheses attempt to explain the altered physiology of women with obesity. At a cellular level, decreased contractility in the myometrium may be responsible.7,20−22 The force and rate of myometrial contractions rely on the influx of calcium into the myocyte. Cholesterol and leptin, which are shown to be increased in women with obesity,
reduce the influx of calcium and antagonize the actions of oxytocin.7,,22 Thus, reduced myometrial contractility may explain prolonged labour, increased oxytocin demands, and higher rates of postdate pregnancies.7,9,21,23 Contrasting outcomes between normal-weight women and women with obesity may not be solely explained by intrinsic patient factors. Consideration should also be given to factors that may affect clinical decision making. Health care providers have been shown to respond differently to patients based on their size.24,25 This weight bias can be explicit (conscious and intentional) or implicit (unconscious and unintentional).26 For example, there may be an implicit tendency to offer a controlled Caesarean delivery rather than pursuing a vaginal delivery, given the unpredictability of labour and the inherent risk of emergency Caesarean delivery. This bias may partly explain the lower rates of operative vaginal delivery in women with obesity.3,5,19 Our study also demonstrated a decreasing trend towards operative vaginal delivery with increasing EOSS category. Physicians may inherently view these patients as high risk for complications such as macrosomia and shoulder dystocia and therefore be hesitant to offer instrumentation, thereby resulting in higher rates of Caesarean delivery. Strengths of this study include the use of multiple centers, a high participation rate, and a comprehensive data set because of the prospective nature of the study. Some limitations, however, should be noted. First, given that overall rates of EOSS category 3 participants were low in this study, attempts should be made to replicate this finding on a larger scale before altering care patterns. Second, varying definitions of overweight and obesity continue to be applied to pregnancy in the literature, thus making it difficult to interpret and compare previous results. At our centres, a maternal weight is rarely documented in the preconception phase, and as such accurate pre-pregnancy weights are unavailable. Self-reported weights have often been used, but weights, and the degree of obesity, may be underreported, particularly in patients at higher BMI.27−29 As such, we used a measured weight at first antenatal visit. This is the earliest and most readily available assessment of measured weight that can be used in clinical decision making at point of care. Because patients may have gained some weight in early pregnancy, there may be an overestimation of overweight in this study. This should have diminished results only by theoretically including more normal-weight women, and therefore a lower-risk population of women, into the sample group. Despite this, after removing all women with a self-reported BMI <25.0 kg/m2, we still observed a high rate of Caesarean delivery in our EOSS category 3.
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Third, obesity-related comorbidities were documented on the basis of a combination of self-reported medical history and medical records. Therefore, there may be an underreporting of medical comorbidities. Because of the young age of obstetrics patients, many have had limited interactions with the health care system before their pregnancy. Many obesity-related conditions such as non-alcoholic fatty liver disease, dyslipidemia, and obstructive sleep apnea are initially asymptomatic or unrecognized and require screening for diagnosis. Therefore, these conditions may have not yet been recognized and would be underestimated in the confines of this study. Finally, in examining secondary outcomes on the basis of a summary score, all outcomes were weighted equally. Outcomes with more significant clinical impact, such as stillbirth or maternal death, should potentially be weighted more heavily. In addition, a summary score does not provide insight into individual adverse outcomes that would need to be studied separately to ensure adequate power and to draw appropriate conclusions. CONCLUSION
Given the significant morbidity associated with Caesarean delivery, particularly after a failed induction of labour, ascertaining guidance in managing these patients would be helpful to mitigate risk. To date, BMI has inadequately assessed the risk of Caesarean delivery in women with overweight and obesity who are undergoing an induction of labour. The EOSS, however, provides a superior method of determining women at high risk for this outcome. Acknowledgements
This research was funded by generous supporters of the Lois Hole Hospital for Women through the Women & Children’s Health Research Institute and the Department of Obstetrics and Gynecology at the University of Alberta. REFERENCES 1. Statistics Canada. Table 13-10-0096-20 Body mass index, overweight or obese, self-reported, adult, age groups (18 years and older). Available at: https://www150.statcan.gc.ca/t1/tbl1/en/tv.action?pid=1310009620. Accessed on December 3, 2018. 2. Statistics Canada. Table 17-10-0008-01 Estimates of the components of demographic growth, annual. Available at:https://www150.statcan.gc.ca/ t1/tbl1/en/tv.action?pid=1710000801. Accessed on December 3, 2018. 3. Baron CM, Girling LG, Mathieson AL, et al. Obstetrical and neonatal outcomes in obese parturients. J Matern Fetal Neonatal Med 2010;23:906–13. 4. Chu SY, Kim SY, Schmid CH, et al. Maternal obesity and risk of cesarean delivery: a meta-analysis. Obes Rev 2007;8:385–94.
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5. El-Chaar D, Finkelstein SA, Tu X, et al. The impact of increasing obesity class on obstetrical outcomes. J Obstet Gynaecol Can 2013;35:224– 33. 6. Feresu SA, Wang Y, Dickinson S. Relationship between maternal obesity and prenatal, metabolic syndrome, obstetrical and perinatal complications of pregnancy in Indiana, 2008-2010. BMC Pregnancy Childbirth 2015;15. 266.e1−10. 7. Zhang J, Bricker L, Wray S, et al. Poor uterine contractility in obese women. BJOG 2007;114:343–8. 8. Aune D, Saugstad OD, Henriksen T, et al. Maternal body mass index and the risk of fetal death, stillbirth, and infant death: a systematic review and meta-analysis. JAMA 2014;311:1536–46. 9. Stotland NE, Washington AE, Caughey AB. Prepregnancy body mass index and the length of gestation at term. Am J Obstet Gynecol 2007;197:378.e1–5. 10. Vinturache A, Moledina N, McDonald S, et al. Pre-pregnancy body mass index (BMI) and delivery outcomes in a Canadian population. BMC Pregnancy Childbirth 2014;14. 422.e1−10. 11. Subramaniam A, Jauk VC, Goss AR, et al. Mode of delivery in women with class III obesity: planned cesarean compared with induction of labor. Am J Obstet Gynecol 2014;211:700.e1–9. 12. Sharma AM, Kushner RF. A proposed clinical staging system for obesity. Int J Obes (Lond) 2009;33:289–95. 13. Kuk JL, Ardern CI, Church TS, et al. Edmonton Obesity Staging System: association with weight history and mortality risk. Appl Physiol Nutr Metab 2011;36:570–6. 14. Padwal RS, Pajewski NM, Allison DB, et al. Using the Edmonton obesity staging system to predict mortality in a populationrepresentative cohort of people with overweight and obesity. CMAJ 2011;183:1059–66. 15. Chiappetta S, Stier C, Squillante S, et al. The importance of the Edmonton Obesity Staging System in predicting postoperative outcome and 30-day mortality after metabolic surgery. Surg Obes Relat Dis 2016;12:1847–55. 16. Patterson N, Sharma AM, Maxwell C, et al. Obesity-related health status is a better predictor of pregnancy with fertility treatment than body mass index: a prospective study. Clin Obes 2016;6:243–8. 17. Davies GA, Maxwell C, McLeod L. Obesity in pregnancy. J Obstet Gynaecol Can 2018;40:8.e630–9. 18. O’Dwyer V, O’Kelly S, Monaghan B, et al. Maternal obesity and induction of labor. Acta Obstet Gynecol Scand 2013;92:1414–8. 19. Ronzoni S, Rosen H, Melamed N, et al. Maternal obesity class as a predictor of induction failure: a practical risk assessment tool. Am J Perinatol 2015;32:1298–304. 20. Zhang J, Kendrick A, Quenby S, et al. Contractility and calcium signaling of human myometrium are profoundly affected by cholesterol manipulation: implications for labour? Reprod Sci 2007;14:456–66. 21. Roloff K, Peng S, Sanchez-Ramos L, et al. Cumulative oxytocin dose during induction of labor according to maternal body mass index. Int J Gynaecol Obstet 2015;131:54–8. 22. Wuntakal R, Kaler M, Hollingworth T. Women with high BMI: Should they be managed differently due to antagonizing action of leptin in labour? Med Hypotheses 2013;80:767–8. 23. Lassiter JR, Holliday N, Lewis DF, et al. Induction of labor with an unfavorable cervix: how does BMI affect success? J Matern Fetal Neonatal Med 2016;29:3000–2.
The Edmonton Obesity Staging System Predicts Mode of Delivery After Labour Induction
24. Hebl MR, Xu J. Weighing the care: physicians’ reactions to the size of a patient. Int J Obes 2001;25:1246–52.
27. Russell A, Gillespie S, Satya S, et al. Assessing the accuracy of pregnancy women in recalling pre-pregnancy weight and gestational weight gain. J Obstet Gynaecol Can 2013;35:802–9.
25. Jackson SE, Beeken RJ, Wardle J. Obesity, perceived weight discrimination, and psychological well-being in older adults in England. Obesity 2015;23:1105–11.
28. Gaudet LM, Gruslin A, Magee LA. Weight in pregnancy and its implications: what women report. J Obstet Gynaecol Can 2011;33:227–34.
26. Phelan SM, Dovidio JF, Puhl RM, et al. Implicit and explicit weight bias in a national sample of 4,732 medical students: the medical student CHANGES study. Obesity 2014;22:1201–8.
29. Gorber SC, Tremblay M, Moher D, et al. A comparison of direct vs. selfreport measures for assessing height, weight and body mass index: a systematic review. Obes Rev 2007;8:307–26.
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The Edmonton Obesity Staging System Predicts Mode of Delivery After Labour Induction Ashley Nicole Demsky, MD, MSc;1 Shawna Marie Stafford, MD, MSc;1 Daniel Birch, MD, MSc;2 Arya M. Sharma, MD;3 Jane Ann Schulz, MD;1 Helen Steed, MD1 1
Department of Obstetrics and Gynecology, Lois Hole Hospital for Women, University of Alberta, Edmonton, AB
2
Department of Surgery and Center for the Advancement of Minimally Invasive Surgery, Royal Alexandra Hospital, University of Alberta, Edmonton, AB 3
Department of Medicine, University of Alberta, Edmonton, AB
A.N. Demsky
Abstract Objective: This study sought to evaluate the use of the Edmonton Obesity Staging System (EOSS) in predicting Caesarean delivery among term, nulliparous, and singleton pregnancies in women with overweight or obesity who are undergoing an induction of labour. Methods: A prospective cohort study was performed in Edmonton, Alberta. Women undergoing an induction of labour at term were recruited to either a sample cohort, including women with a body mass index of ≥25.0 kg/m2 at first antenatal visit, or a control cohort with a body mass index of 18.5 to 24.9 kg/m2. Participating women provided a self-reported health history and consented to review of their medical records allowing allocation into EOSS categories. The primary outcome was the rate of Caesarean delivery based on EOSS category. Secondary outcomes consisted of a summary score of adverse maternal, delivery, and neonatal events (Canadian Task Force Classification II-2). Results: Overall, 345 women were recruited, with a participation rate of 93.7%. The sample cohort consisted of 276 women with overweight or obesity, whereas the control cohort included 69 normal-weight women. The overall rate of Caesarean delivery was 30.4% for the control cohort and 35.8%, 29.9%, 43.2%, and 90.5% for women assigned an EOSS category 0, 1, 2, and 3, respectively (P < 0.001). A summary score was not indicative of overall rate of adverse maternal, delivery, and neonatal events (P = 0.22). Conclusion: The EOSS may help predict the chance of Caesarean delivery in a high-risk group of nulliparous women with Key Words: Obesity, labour induction, body mass index (BMI), Edmonton Obesity Staging System (EOSS), Caesarean delivery Corresponding author: Dr. Ashley Nicole Demsky, Department of Obstetrics and Gynecology, Lois Hole Hospital for Women, University of Alberta, Edmonton, AB. [email protected] Competing interests: See Acknowledgements. Each author has indicated that they meet the journal’s requirements for authorship. Received on February 19, 2019 Accepted on August 15, 2019
overweight or obesity who are undergoing an induction of labour at term.
Résumé tude visait a e valuer l’utilisation du syste me de Objectif : Cette e site EOSS (Edmonton Obesity Staging classification de l’obe dire la probabilite d’un accouchement par System) pour pre sarienne en cas de de clenchement artificiel du travail d’une ce terme chez une femme nullipare en grossesse monofœtale a site . surpoids ou atteinte d’obe tude de cohorte prospective a e te re alise e a Méthodologie : Une e des femmes Edmonton en Alberta. Les chercheurs ont recrute clenchement artificiel du travail d’une grossesse devant subir un de terme et les ont re parties en deux groupes : soit dans un groupea chantillon de femmes ayant un indice de masse corporelle de 25,0 e re consultation de suivi pre natal, soit kg/m2 ou plus lors de la premie moin de femmes ayant un indice de masse dans un groupe te 24,9 kg/m2. Les participantes ont autode clare corporelle de 18,5 a ce dents me dicaux et consenti a l’examen de leur dossier leurs ante dical aux fins de classification en fonction des cate gories de me sariennes fonde sur la classification de l’EOSS. Le taux de ce re de jugement principal. Les crite res de l’EOSS constituait le crite jugement secondaires consistaient en un indice global des ve nements de favorables maternels, obste tricaux et ne onataux e tude canadien sur les soins de (classification II-2 du Groupe d’e pre ventifs). sante te recrute es pour cette e tude, Résultats : Un total de 345 femmes ont e sente un taux de participation de 93,7 %. Le groupelaquelle pre chantillon se compose de 276 femmes en surpoids ou atteintes e site , tandis que le groupe te moin comprend 69 femmes de d’obe sariennes global est de 30,4 % pour les poids normal. Le taux de ce moin et de 35,8 %, 29,9 %, 43,2 % et 90,5 % femmes du groupe te es dans les cate gories 0, 1, respectivement pour les femmes classe re 2 et 3 selon l’EOSS (P < 0,001). Un indice global ne s’est pas ave ve lateur du taux global d’e ve nements de favorables maternels, re tricaux et ne onataux (P = 0,22). obste pre dire la probabilite Conclusion : L’EOSS pourrait aider a sarienne dans un groupe a risque e leve de d’accouchement par ce site en cas de femmes nullipares en surpoids ou atteintes d’obe clenchement artificiel du travail d’une grossesse a terme. de
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© 2019 The Society of Obstetricians and Gynaecologists of Canada/La Société des obstétriciens et gynécologues du Canada. Published by Elsevier Inc. All rights reserved.
J Obstet Gynaecol Can 2019;000(000):1−9 https://doi.org/10.1016/j.jogc.2019.08.022
INTRODUCTION
besity has become the most prevalent chronic disease affecting women of reproductive age. Approximately 20% of Canadian women aged 18 to 34 have obesity.1 With over 380 000 births in Canada per year, an estimated 76 000 are therefore affected by this condition.2 Excess maternal weight is associated with adverse events in pregnancy, including increased rates of hypertensive disorders, gestational diabetes, abnormal labour patterns, and, most importantly, obstetrical interventions such as Caesarean delivery.3−7 The risks of stillbirth and fetal death are also augmented.8 Furthermore, high body mass index (BMI) is associated with an increased need for an induction of labour as a result of both complications related to pregnancy and prolonged gestations.9,10 This intervention compounds delivery-related risk for women with obesity because women whose labour is induced are more likely to undergo an emergency Caesarean delivery.10 An emergency Caesarean delivery after a failed induction of labour carries a higher rate of complications than a vaginal delivery or elective Caesarean delivery.11 As such, prevention of emergency Caesarean delivery is instrumental in reducing morbidity for women with obesity in pregnancy.
O
Historically, BMI has been used to stratify obesity-related risk for women at term. Traditional thinking is that as BMI increases, so does the risk of adverse outcomes, including Caesarean delivery. Not all women, however, are equally affected by obesity. For example, two women with a BMI of 35 kg/m2 may be affected differently: One woman may have no obesity-related comorbidities, and the second may have a history of depression, gestational diabetes, and gallbladder disease. Excess weight will affect the global health status of the second patient to a greater degree. BMI alone fails to convey these differences and cannot accurately predict which patient is at higher risk of Caesarean delivery. Accurate prediction of Caesarean delivery would be useful for care providers. Should risk of emergency Caesarean delivery be excessive and chance of low-risk vaginal delivery be minimal, planning for elective Caesarean delivery could help mitigate risks associated with emergency surgery. A more accurate approach to delineate which women will be at highest risk for Caesarean delivery is needed. The
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Edmonton Obesity Staging System (EOSS) has been proposed as a method of determining outcomes in patients with increased weight that is superior to BMI alone.12 The EOSS is a clinical staging system that individualizes risk profiles by incorporating knowledge of a patient’s current health status and weight-related comorbidities. To date, the EOSS has been more successful than BMI at predicting long-term mortality rates, poor postoperative outcomes in non-obstetrical patients, and pregnancy rates in women undergoing fertility treatments.13−16 It has not yet been applied to obstetrical populations. This study aimed to explore the use of the EOSS to predict mode of delivery among women with overweight or obesity who are undergoing an induction of labour. Women who are more affected by obesity-related comorbidities may be at higher risk of Caesarean delivery. We hypothesized that parturients at higher EOSS categories would have an increased rate of Caesarean delivery. METHODS
A prospective cohort study was performed at two highvolume obstetrical centers in Edmonton, Alberta. The Lois Hole Hospital for Women is a tertiary referral center, and the Grey Nuns Hospital is a community hospital. Both perform over 7000 deliveries per annum. Ethical approval was obtained from the Human Research Ethics Board at the University of Alberta (Pro00075527) before commencement of the study. Recruitment was done simultaneously at each site between January 2018 and August 2018. Women scheduled for an induction of labour were screened daily by nursing staff for possible inclusion in the study. Researchers were then contacted for recruitment. All initiated inductions in nulliparous women ≥18 years old at ≥370 gestational age with singleton, vertex pregnancies and documented prenatal care were included. Nulliparity was defined as no previous deliveries ≥20 weeks gestational age. Exclusion criteria included a previous myomectomy, BMI <18.5 kg/m2, midwifery care, presentation for a planned assisted second stage, the presence of congenital fetal anomalies or predetermined fatal fetal outcomes, no prenatal care, and non −English-speaking women. To limit bias, researchers were not involved in patient care; if a researcher provided emergency care, that participant was removed from the study. At recruitment, participants provided written consent. Participants were asked to complete a personal health history. They also consented to a full review of their medical records, including their prenatal, delivery, and current
The Edmonton Obesity Staging System Predicts Mode of Delivery After Labour Induction
Table 1. Edmonton Obesity Staging System Category
Classification
Common disease examples
0
No apparent risk factors
No apparent obesity-related risk factors No physical symptoms No psychopathology No functional limitations No impairment of well-being
1
Subclinical risk factors associated with obesity
Borderline hypertension not requiring medical therapy Impaired glucose tolerance, self-reported or abnormal gestational diabetes screen History of irregular menses of unknown cause Mild physical symptoms related to obesity Mild psychopathology Mild impairment in well-being
2
Established obesity-related chronic disease
Essential or gestational hypertension Gestational diabetes Type 2 diabetes Polycystic ovarian syndrome Use of assisted reproductive technology Dyslipidemia Non-alcoholic fatty liver disease Known gallstones or prior cholecystectomy Osteoarthritis Obstructive sleep apnea Incontinence before pregnancy Moderate psychopathology (depression, anxiety, disordered eating behavior, significant body image disturbance) Moderate impairment of well-being
3
Established obesity-related chronic disease with end-organ damage
Preeclampsia Stroke Myocardial infarction Angina Heart failure Diabetic complications Thromboembolic disease Hepatic dysfunction or hematoma Pulmonary edema Renal insufficiency Incapacitating osteoarthritis Significant impairment of well-being
4
Severe (potentially end-stage) disabilities from obesity-related chronic diseases
Eclampsia Dialysis Bedridden or unable to mobilize Disabling psychopathology and/or severe impairment of well-being
Adapted from Sharma and Kushner.12
hospital admission records. Research participants were stratified into two groups according to their measured weight at their first antenatal visit. The sample cohort consisted of women with a BMI ≥25.0 kg/m2, and the control cohort consisted of normal-weight women with a BMI of 18.5 to 24.9 kg/m2. There were no interventions or alterations to patient care. After enrolment and before delivery, two researchers independently assigned women in the sample cohort to an EOSS category on the basis of their obesity-related comorbidities. The EOSS used in this study has been modified for use in pregnancy by incorporating pregnancy-related
complications that have been previously associated with obesity, such as gestational diabetes and hypertensive disorders of pregnancy (Table 1). Its creator (A.M.S.) reviewed the modified version of this scale for face validity. In patients with multiple comorbidities, the most severe comorbidity determined the EOSS category. Data were entered into REDCap, a secure platform for data storage supported by the University of Alberta. At the conclusion of the study, all records were reviewed for accuracy. Maternal demographics, maternal comorbidities, and labour information were evaluated (Tables 2 and 3).
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Table 2. Maternal characteristics Characteristics
Control n= 69
EOSS 0 n = 53
EOSS 1 n = 77
EOSS 2 n = 125
EOSS 3 n = 21
Demographics Age (years), median (IQR) Smoker, n (%)
30.0 (27.0−32.0) 29.0 (26.0−31.0) 29.0 (25.0−31.0) 30.0 (28.0−33.0) 31.0 (27.0−34.0) 3 (4.3)
0 (0)
7 (9.1)
11 (8.8)
3 (14.3)
Gestational age (weeks and days), median (IQR) Delivery
41.0 (39.6−41.1) 41.1 (40.1−41.3) 41.0 (39.6−41.3) 39.3 (39.1−40.3) 38.3 (37.6−39.3)
First antenatal visit
17.0 (14.4−19.6) 21.6 (16.6−27.0) 21.0 (16.1−24.6) 18.9 (13.0−23.6) 18.1 (13.7−24.7)
BMI, median (IQR) Delivery
27.0 (25.9−28.4) 32.7 (30.6−37.2) 33.4 (30.9−37.6) 35.2 (32.0−41.1) 37.5 (32.8−45.1)
First antenatal visit
22.4 (21.3−23.4) 28.5 (26.6−31.9) 29.1 (26.8−33.2) 31.7 (28.4−38.4) 33.5 (30.4−41.1)
GWG (kg), median (IQR)
13.5 (9.9−16.7)
9.0 (5.7−13.6)
9.7 (6.9−12.8)
10.7 (6.3−12.0)
11.6 (6.8−14.5)
Prostaglandin only
47 (68.1)
35 (66.0)
51 (66.2)
90 (72.0)
9 (42.9)
Oxytocin
15 (21.7)
8 (15.1)
17 (22.1)
14 (11.2)
3 (14.3)
Foley catheter only
2 (2.9)
3 (5.7)
5 (6.5)
4 (3.2)
3 (14.3)
Combineda
3 (4.3)
3 (5.7)
2 (2.6)
8 (6.4)
2 (9.5)
b
2 (2.9)
3 (5.7)
2 (2.6)
2 (9.5)
4 (19.0)
0 (0)
1 (1.9)
0 (0)
0 (0)
0 (0)
Primary mode of induction, n (%)
Sequential ARM
Cervical dilation at admission (cm), median (IQR)
2.5 (1.5−3.0)
2.0 (1.0−3.0)
3.0 (1.5−3.0)
3.0 (1.5−3.0)
1.0 (0.0−2.0)
GBS positive, n (%)
11 (15.9)
9 (17.0)
11 (14.3)
27 (21.6)
5 (23.8)
Epidural use, n (%)
59 (85.5)
42 (79.2)
68 (88.3)
108 (86.4)
14 (66.7)
Received ARM, n (%)
46 (66.7)
25 (47.2)
51 (66.2)
81 (64.8)
14 (66.7)
Received oxytocin, n (%)
53 (76.8)
44 (83.0)
66 (85.7)
108 (86.4)
20 (95.2)
Birth weight (g), median (IQR)
3370 (3110−3550)
a
Combined, Foley catheter induction with simultaneous prostaglandin insertion.
b
Sequential, Foley catheter induction after a trial of prostaglandin induction.
3590 (3280−3880)
3580 (3230−3910)
3450 (3140−3710)
3300 (2830−3570)
ARM: artificial rupture of membranes; BMI: body mass index; EOSS: Edmonton Obesity Staging System; GWG: gestational weight gain; IQR: interquartile range.
Variables were recorded from a combination of selfreported data or as documented on hospital records.
admission to the neonatal intensive care unit, maternal death, thromboembolic disease, and mode of delivery.
The primary outcome was rate of Caesarean delivery. The secondary outcome consisted of a summary score of maternal, delivery, and neonatal outcomes. This included the incidence of excessive gestational weight gain, according to the Society of Obstetricians and Gynaecologists of Canada recommended weight gain guidelines (BMI 18.5− 24.9 kg/m2, >16.0 kg; BMI 25.0−29.9 kg/m2, >11.5 kg; BMI ≥30.0 kg/m2, >7.0 kg),17 polyhydramnios or oligohydramnios, chorioamnionitis, abruption, shoulder dystocia, severe perineal tear (≥third-degree tear or episiotomy), manual removal of placenta, excessive blood loss (estimated blood loss >500 mL in vaginal delivery or >1000 mL in Caesarean delivery), blood transfusion, meconium, low Apgar score (≤7 at 1 and 5 minutes), stillbirth after initiation of induction, abnormal birth weight (<2500g or ≥4000g),
The sample size calculation is based on predicted proportion of Caesarean section rate for each category. We anticipated that the emergency Caesarean delivery rate of normal-weight control subjects, after an induction of labour, would be approximately 20%.18 With each increase in EOSS category, there should be an increase in Caesarean delivery rate. Calculations were based on the estimate that the Caesarean delivery rate in the EOSS category 0, 1, 2, and 3 would approach 30%, 35%, 40%, and 45%, respectively. EOSS stage 4 was excluded from our sample size calculation because the presentation of individuals with this degree of illness was unlikely to be encountered. This resulted in a sample size calculation of 345 patients, including EOSS stages 0 to 3 and a group of normal-weight control subjects. Overall, this sample size of 345 achieves 80%
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Table 3. Summary score and secondary outcomes by Edmonton Obesity Staging System category Control n = 69
EOSS 0 n = 53
EOSS 1 n = 77
EOSS 2 n = 125
EOSS 3 n = 21
1.83 § 1.26
2.02 § 1.28
2.06 § 1.37
2.13 § 1.36
2.62 § 1.66
21 (30.4)
26 (49.1)
41 (53.2)
63 (50.4)
14 (66.7)
Outcome Summary score (P = 0.22) Excessive GWG Abnormal fluid level
2 (2.9)
1 (1.9)
3 (3.9)
4 (3.2)
1 (4.8)
Chorioamnionitis
1 (1.4)
4 (7.5)
6 (7.8)
11 (8.8)
1 (4.8)
Abruption
1 (1.4)
0 (0)
2 (2.6)
3 (2.4)
0 (0)
0 (0)
2 (3.8)
6 (7.8)
6 (4.8)
0 (0)
Severe perineal tear
19 (27.5)
14 (25.4)
12 (15.6)
22 (17.6)
0 (0)
Manual removal of placenta
7 (10.1)
1 (1.9)
2 (2.6)
6 (4.8)
0 (0)
Excessive blood loss
5 (7.2)
10 (18.9)
12 (15.6)
21 (16.8)
5 (23.8)
Blood transfusion
1 (1.4)
0 (0)
0 (0)
0 (0)
1 (4.8)
15 (21.7)
11 (20.8)
18 (23.4)
22 (17.6)
4 (19.0)
8 (11.6)
2 (3.8)
4 (5.2)
9 (7.2)
3 (14.3)
0 (0)
0 (0)
0 (0)
1 (0.8)
0 (0)
Abnormal birth weight
6 (8.7)
7 (13.2)
17 (22.1)
18 (14.4)
3 (14.3)
Admission to NICU
1 (1.4)
1 (1.9)
2 (2.6)
7 (5.6)
2 (9.5)
Shoulder dystocia
Meconium Low Apgar scores Stillbirth
Maternal death
0 (0)
0 (0)
0 (0)
0 (0)
0 (0)
Thromboembolic disease
0 (0)
0 (0)
0 (0)
0 (0)
1 (4.8)
Instrumental delivery
Caesarean delivery
18 (26.1)a -Forceps, 13 (72.2) -Vacuum, 6 (33.3) 21 (30.4)
9 (17.0) -Forceps, 8 (88.9) -Vacuum, 1 (11.1) 19 (35.8)
a
Includes one combined vacuum and forceps.
b
Includes a failed instrumental delivery resulting in a Caesarean delivery.
11 (14.3) -Forceps, 11 (100) -Vacuum, 0 (0) 23 (29.9)
18 (14.4) -Forceps, 16 (88.9) -Vacuum, (11.1) 54 (43.2)
1 (4.8)b -Forceps, 0 -Vacuum, 1 (100) 19 (90.5)
NICU: neonatal intensive care unit; EOSS: Edmonton Obesity Staging System; GWG: gestational weight gain. Data are presented as mean § SD or n (%).
power using the 4 degrees of freedom chi-square test with a significance level (alpha) of 0.05. For the primary outcome, Pearson chi-square tests were used to detect differences among groups with categorical variables. Binomial logistic regression was performed to ascertain odds ratios (ORs). For the secondary outcome, a one-way analysis of variance was conducted to determine whether differences in mean summary scores existed. For all analyses, a statistical difference was taken at a P ≤ 0.05 level of significance. In instances where pairwise comparisons were performed, the type I error was adjusted for multiplicity using Bonferroni correction, and a P value of ≤0.05 remained statistically significant. All statistical analyses were performed using SAS software version 9.4 (SAS Institute Inc., Cary, NC). RESULTS
Overall, 397 patients were approached for recruitment into the study from January 2018 to August 2018 (Figure 1).
Twenty-five women declined to participate, thus yielding an overall participation rate of 93.7%. An additional 27 women were excluded (Figure 1). A total of 154 (55.8%) women from the sample cohort and 36 (52.2%) women from the control cohort were recruited from the tertiary care center, with the remainder derived from the community hospital. Maternal demographics and group characteristic information is presented in Table 2. The control cohort consisted of a total of 69 (20%) women. The sample cohort consisted of 53 (15.4%), 77 (22.3%), 125 (36.2%), and 21 (6.1%) women distributed by EOSS category 0, 1, 2, and 3, respectively. Distribution of the sample cohort by BMI class at first antenatal visit resulted in 129 (39.5%) classified as having overweight (BMI 25.0−29.9 kg/m2) and 147 (42.6%) classified as having obesity (BMI ≥30.0 kg/m2). If further divided by obesity class, there were 74 (50.3%), 39 (26.5%), and 34 (23.1%) in class I (BMI 30.0−34.9 kg/m2), II (BMI 35.0−39.9 kg/m2), and III (BMI ≥40.0 kg/m2), respectively.
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Figure 1. Study cohort selection flow chart.
Figure 2. Rate of Caesarean delivery by Edmonton Obesity Staging System (EOSS) category (P < 0.001).
The rate of Caesarean delivery by EOSS category is presented in Figure 2. Baseline rate of Caesarean delivery for the control cohort was 30.4%. When stratified by EOSS category, 35.8%, 29.9%, 43.2%, and 90.5% of women underwent Caesarean delivery in EOSS category 0, 1, 2, and 3, respectively (P < 0.001). Pairwise comparisons and binomial logistic regression were performed to ascertain the effect of EOSS category on Caesarean delivery. In unadjusted analysis there was no difference in EOSS category 0 (OR 1.3; 95% confidence interval [CI] 0.6−2.7; P = 0.53), EOSS Category 1 (OR 0.97; 95% CI 0.5−2.0; P = 0.94), and EOSS category 2 (OR 1.7; 95% CI 0.9−3.2; P = 0.08). There was significance for EOSS category 3 (OR 21.7; 95% CI 4.6−101.8; P < 0.001). There was no
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statistically significant difference when the model was adjusted by age (P = 0.07) or mode of induction (P = 0.44). Artificial rupture of membranes as a primary mode of induction was not included in the analysis because of the low frequency of occurrence. The rate of Caesarean delivery was also reviewed after excluding all women with a self-reported BMI <25.0 kg/m2 to assess whether any significant misclassification may have altered the described outcomes. This yielded 210 patients, and overall Caesarean delivery rates showed a similar trend, with the highest rate of Caesarean delivery in EOSS category 3 (EOSS 0, n = 14 [40.0%]; EOSS 1, n = 13 [25.0%]; EOSS 2, n = 46 [44.2%]; EOSS 3, n = 17 [89.5%]; P < 0.001). The most common indication for Caesarean delivery was fetal heart rate abnormalities; this was the same for each patient category (control, 42.9%; EOSS 0, 47.3%; EOSS 1, 60.9%; EOSS 2, 57.4%; EOSS 3, 47.4%). Failure to progress in the first stage of labour was the second most common indication (control, 38.1%; EOSS 0, 31.6%; EOSS 1, 39.1%; EOSS 2, 38.9%; EOSS 3, 31.6%). Multiple indications for Caesarean delivery were sometimes provided. Rates of Caesarean delivery were then compared by BMI. Overall rate of Caesarean delivery was 39.5%, 40.5%, 43.6%, and 50.0% for overweight, obesity class I, class II, and class III, respectively. The difference in proportion of Caesarean delivery between weight classes did not reach statistical significance (P = 0.37).
The Edmonton Obesity Staging System Predicts Mode of Delivery After Labour Induction
Finally, secondary outcomes were analyzed using a summary score of adverse maternal, delivery, and neonatal events (Table 3). There was one perinatal death in this study, in an EOSS category 2 participant. The patient was known to have poorly controlled gestational diabetes. She received an induction of labour with prostaglandins that was subsequently complicated by uterine tachysystole. After removal of the prostaglandin and resolution of the tachysystole, she refused further intervention and left against medical advice. After 1 week she presented again for induction with an unexplained fetal death. DISCUSSION
Obesity in pregnancy presents an ongoing challenge for maternity care providers. Our study is consistent with previous reports that determined higher rates of Caesarean delivery in women with overweight and obesity when compared with normal-weight women.18,19 Despite this, there was no statistically significant impact of BMI class on mode of delivery. Therefore, BMI stratification provides no significant predictive utility and is not clinically powerful enough to guide recommendations for mode of delivery. In contrast, the EOSS more clearly delineates a subpopulation of women who are at a high risk of Caesarean delivery. When the EOSS is applied, the rate of Caesarean delivery in the high-risk subpopulation (EOSS category 3) is over 90%. Moreover, Caesarean delivery rates in the EOSS 0 and 1 categories were no higher than in the control populations despite a markedly higher BMI than in control subjects. Given that emergency Caesarean delivery carries the highest complication rate, and that women classed as an EOSS category 3 are at over a 90% risk of this outcome, interventions should be focused at preventing or reducing the morbidity in EOSS category 3 women. Should EOSS category 3 classification persist in pregnancy, patients may be offered an elective Caesarean delivery instead of an induction of labour. This may avoid the morbidity associated with emergency Caesarean delivery, allow for improved resource planning, and spare women from an induction process with a >90% chance of failure. The EOSS may be better able to predict Caesarean delivery at the higher EOSS category because it identifies those women who have been most affected by excess adiposity. Some hypotheses attempt to explain the altered physiology of women with obesity. At a cellular level, decreased contractility in the myometrium may be responsible.7,20−22 The force and rate of myometrial contractions rely on the influx of calcium into the myocyte. Cholesterol and leptin, which are shown to be increased in women with obesity,
reduce the influx of calcium and antagonize the actions of oxytocin.7,,22 Thus, reduced myometrial contractility may explain prolonged labour, increased oxytocin demands, and higher rates of postdate pregnancies.7,9,21,23 Contrasting outcomes between normal-weight women and women with obesity may not be solely explained by intrinsic patient factors. Consideration should also be given to factors that may affect clinical decision making. Health care providers have been shown to respond differently to patients based on their size.24,25 This weight bias can be explicit (conscious and intentional) or implicit (unconscious and unintentional).26 For example, there may be an implicit tendency to offer a controlled Caesarean delivery rather than pursuing a vaginal delivery, given the unpredictability of labour and the inherent risk of emergency Caesarean delivery. This bias may partly explain the lower rates of operative vaginal delivery in women with obesity.3,5,19 Our study also demonstrated a decreasing trend towards operative vaginal delivery with increasing EOSS category. Physicians may inherently view these patients as high risk for complications such as macrosomia and shoulder dystocia and therefore be hesitant to offer instrumentation, thereby resulting in higher rates of Caesarean delivery. Strengths of this study include the use of multiple centers, a high participation rate, and a comprehensive data set because of the prospective nature of the study. Some limitations, however, should be noted. First, given that overall rates of EOSS category 3 participants were low in this study, attempts should be made to replicate this finding on a larger scale before altering care patterns. Second, varying definitions of overweight and obesity continue to be applied to pregnancy in the literature, thus making it difficult to interpret and compare previous results. At our centres, a maternal weight is rarely documented in the preconception phase, and as such accurate pre-pregnancy weights are unavailable. Self-reported weights have often been used, but weights, and the degree of obesity, may be underreported, particularly in patients at higher BMI.27−29 As such, we used a measured weight at first antenatal visit. This is the earliest and most readily available assessment of measured weight that can be used in clinical decision making at point of care. Because patients may have gained some weight in early pregnancy, there may be an overestimation of overweight in this study. This should have diminished results only by theoretically including more normal-weight women, and therefore a lower-risk population of women, into the sample group. Despite this, after removing all women with a self-reported BMI <25.0 kg/m2, we still observed a high rate of Caesarean delivery in our EOSS category 3.
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OBSTETRICS
Third, obesity-related comorbidities were documented on the basis of a combination of self-reported medical history and medical records. Therefore, there may be an underreporting of medical comorbidities. Because of the young age of obstetrics patients, many have had limited interactions with the health care system before their pregnancy. Many obesity-related conditions such as non-alcoholic fatty liver disease, dyslipidemia, and obstructive sleep apnea are initially asymptomatic or unrecognized and require screening for diagnosis. Therefore, these conditions may have not yet been recognized and would be underestimated in the confines of this study. Finally, in examining secondary outcomes on the basis of a summary score, all outcomes were weighted equally. Outcomes with more significant clinical impact, such as stillbirth or maternal death, should potentially be weighted more heavily. In addition, a summary score does not provide insight into individual adverse outcomes that would need to be studied separately to ensure adequate power and to draw appropriate conclusions. CONCLUSION
Given the significant morbidity associated with Caesarean delivery, particularly after a failed induction of labour, ascertaining guidance in managing these patients would be helpful to mitigate risk. To date, BMI has inadequately assessed the risk of Caesarean delivery in women with overweight and obesity who are undergoing an induction of labour. The EOSS, however, provides a superior method of determining women at high risk for this outcome. Acknowledgements
This research was funded by generous supporters of the Lois Hole Hospital for Women through the Women & Children’s Health Research Institute and the Department of Obstetrics and Gynecology at the University of Alberta. REFERENCES 1. Statistics Canada. Table 13-10-0096-20 Body mass index, overweight or obese, self-reported, adult, age groups (18 years and older). Available at: https://www150.statcan.gc.ca/t1/tbl1/en/tv.action?pid=1310009620. Accessed on December 3, 2018. 2. Statistics Canada. Table 17-10-0008-01 Estimates of the components of demographic growth, annual. Available at:https://www150.statcan.gc.ca/ t1/tbl1/en/tv.action?pid=1710000801. Accessed on December 3, 2018. 3. Baron CM, Girling LG, Mathieson AL, et al. Obstetrical and neonatal outcomes in obese parturients. J Matern Fetal Neonatal Med 2010;23:906–13. 4. Chu SY, Kim SY, Schmid CH, et al. Maternal obesity and risk of cesarean delivery: a meta-analysis. Obes Rev 2007;8:385–94.
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