Abstract
Objective
Nationally, rates of obesity continue to rise, resulting in increased health concerns for women of reproductive age Identifying the impact of maternal obesity on obstetrical outcomes is important to enhance patient care.
Methods
We conducted a retrospective cohort study of 6674 women who delivered a singleton infant at ≥ 20 weeks’ gestation between December 1, 2007, and March 31, 2010, at The Ottawa Hospital. Maternal pre-pregnancy BMI was used to classify women into normal, overweight, and obese (class I/II/III) categories according to WHO classifications. Obstetrical outcomes among obese women were compared with those of women with normal BMI Multivariable regression models were used to determine adjusted odds ratios and 95% confidence intervals.
Results
Compared with women with normal BMI, obese women had significantly higher rates of preeclampsia, gestational hypertension, and gestational diabetes, and these rates increased with increasing BMI (trend-test P < 0.001). There was a significant increase in rates of induction of labour in the obesity categories, from 25 3% in women with normal BMI to 42 9% in women with class III morbid obesity (aOR 1.67; 95% CI 1.43 to 1.93). Rates of primary Caesarean section rose with increasing BMI and were highest in women with class III morbid obesity (36 2% vs 22 1% in women with normal BMI) (aOR 1.46; 95% CI 1. 23 to 1.73).
Conclusion
Increasing BMI is associated with increasing rates of preeclampsia, gestational hypertension, and gestational diabetes There is a significant increase in rates of induction of labour with increasing obesity class, and a significantly increased Caesarean section rate with higher BMI Obstetrical care providers should counsel obese patients about the risks they face and the importance of weight loss before pregnancy.
Résumé
Objectif
À l´échelle nationale, les taux d´obésité continuent d´augmenter, ce qui occasionne une hausse des préoccupations en matière de santé pour ce qui est des femmes en âge de procréer. Pour en venir à améliorer les soins offerts aux patientes, il est important de s´affairer à identifier les effets de l´obésité maternelle sur les issues obstétricales.
Méthodes
Nous avons mené une étude de cohorte rétrospective qui portait sur 6 674 femmes ayant accouché (entre le 1er décembre 2007 et le 31 mars 2010 à L´Hôpital d´Ottawa) à ≥ 20 semaines de gestation à la suite d´une grossesse monofoetale. L´IMC maternel prégrossesse a été utilisé pour répartir, en fonction des classifications de l´OMS, les femmes en trois catégories: normale, surplus de poids et obèse (classes I/II/III). Les issues obstétricales chez les femmes obèses ont été comparées à celles qu’ont connues les femmes présentant un IMC normal. Des modeles de régression multivariable ont été utilisés pour déterminer les rapports de cotes corrigés et les intervalles de confiance à 95%.
Résultats
Par comparaison avec les femmes présentant un IMC normal, les femmes obèses ont connu des taux considérablement accrus de prééclampsie, d’hypertension gestationnelle et de diabète gestationnel; de plus, ces taux étaient directement proportionnels à l’IMC (test de tendance P < 0,001). Nous avons constaté une hausse significative des taux de déclenchement du travail dans les catégories « obésité », de 25,3 % chez les femmes présentant un IMC normal à 42,9 % chez les femmes présentant une obésité morbide de classe III (RCc 1,67; IC à 95 %, 1,43 - 1,93). Les taux de césarienne primaire étaient directement proportionnels à l’IMC et atteignaient leur apogée chez les femmes présentant une obésité morbide de classe III (36,2 % vs 22,1 % chez les femmes présentant un IMC normal) (RCc 1,46; IC à 95 %, 1,23 - 1,73).
Conclusion
La hausse de l’IMC est associée à la hausse des taux de prééclampsie, d’hypertension gestationnelle et de diabète gestationnel. Les taux de declenchement du travail augmentent de façon significative en fonction de la classe d’obésité; les taux de césarienne connaissent également une hausse considérable au fur et à mesure que s’élève l’IMC. Les fournisseurs de soins obstétricaux devraient aborder, avec leurs patientes obèses, les risques auxquels elles font face et l’importance de la perte de poids avant la grossesse.
Key Words
ABBREVIATIONS
BORNBetter Outcomes Registry & Network
PPROMpreterm pre-labour rupture of membranes
PROMpre-labour rupture of membranes
INTRODUCTION
Rates of obesity, including an increased prevalence of morbid obesity (BMI > 35), are rising dramatically in developed countries.
1.
, 2.
, 3.
, 4.
This trend has led to a concurrent increase in health concerns for women of reproductive age,1.
,4.
and it is now well established that weight gain and obesity cause major comorbidities in pregnancy that contribute to adverse maternal and neonatal outcomes.5.
,6.
In pregnant women, obesity has been shown to increase the likelihood of gestational diabetes,
7.
hypertensive diseases of pregnancy,8.
and severe hypertensive sequelae such as preeclampsia and HELLP syndrome.7.
Obesity may lead to a number of adverse obstetrical outcomes, including an increase in rates of Caesarean section,9.
,10.
prolonged delivery interval,11.
and increased operative time and blood loss.11.
Rates of perinatal death and stillbirth,12.
as well as infant morbidity,8.
,13.
,14.
are also higher in obese populations. Following delivery, maternal health remains an issue, as obese mothers are at higher risk of postpartum hemorrhage,15.
venous thromboembolism,16.
endomyometritis,17.
prolonged hospitalization,15.
and wound infection and dehiscence.7.
,17.
, 18.
, 19.
Finally, obesity plays a role in future pregnancies; obese women are more likely to require a repeat CS because of their lower rate of successful vaginal birth after CS.17.
,20.
,21.
Understanding the continuing development of trends in obesity and obstetrical and perinatal outcomes is integral to maintaining relevant clinical guidelines that ensure high quality care. In particular, there is a need to understand the impact of various levels of obesity during pregnancy, specifically the effect of morbid obesity. The primary aim of our study, therefore, was to examine how increasing obesity class affects adverse obstetrical outcomes and interventions in labour.
MATERIALS AND METHODS
We collected data retrospectively from mothers who gave birth to one infant between December 1, 2007, and March 31, 2010, at a tertiary care centre in south-eastern Ontario. Only mothers with a known pre-pregnancy BMI (or height and pre-pregnancy weight) who delivered at > 20 weeks’ gestation were included in the study. Underweight mothers (BMI < 18.5) were excluded from the sample. All participants had their infants delivered by an on-call family physician or obstetrician.
Data for this study were obtained from Better Outcomes Registry & Network Ontario’s Niday Perinatal Database, an Internet-based birth record system. The database was used to identify the study population. The study centre is a participant in the BORN database and transcribes patient information to the registry. This database is administered by the Children’s Hospital of Eastern Ontario and has a 100% capture rate for hospital births in Ontario. The Niday database includes information on maternal demographic characteristics and health behaviours, preexisting maternal health problems, obstetric complications, intrapartum interventions, and birth outcomes. When a woman is admitted to hospital for delivery, data are collected from medical records, clinical forms, and patient interviews. After the birth, these data are either entered into the database through a secure website by hospital staff or uploaded directly from hospitals that have electronic record capability. An ongoing program of data verification, quality checks, and formal training sessions for individuals collecting and entering data into the system assures that a high level of data quality is maintained.
22.
Maternal pregnancy and intrapartum outcomes examined in the study included preeclampsia, gestational hypertension, gestational diabetes, pre-labour rupture of membranes, preterm pre-labour rupture of membranes, preterm labour, labour induction, Caesarean section (elective vs. emergency, primary vs. repeat), assisted vaginal delivery, and type of labour analgesia. The definition of these outcomes was based on the clinical diagnosis made by the caregiver when completing the form used for input to the database. Elective Caesarean section included both women presenting for a primary CS and women scheduled for an elective repeat CS. Emergency Caesarean section was defined as a procedure that was not planned by the care provider and patient and occurred because of maternal or fetal complications. Maternal demographic characteristics included in the study were maternal age, parity, pre-gestational diabetes mellitus, chronic hypertension, asthma, smoking, geographic area of residence (rural vs. urban), and neighbourhood education and family income quartiles. Data on neighbourhood-level education, income, and geographic area of residence were obtained by linking the perinatal database with Statistics Canada’s Postal Code Conversion File Plus (PCCF+), which contains information from the 2006 Canadian census.
23.
Women were categorized by pre-pregnancy BMI, defined as weight in kilograms divided by the square of height in meters (kg/m2). BMI categories were based on World Health Organization standards and were defined as follows: normal (18.5 to 24.9 kg/m2), overweight (25.0 to 29.9 kg/m2), and obese (class I: 30 to 34.9 kg/m2; class II: 35 to 39.9 kg/m2; class III: ≥ 40 kg/m2).
24.
Study outcomes were calculated for overweight and obese women and were compared with women in the normal BMI group. T-tests for continuous variables and Pearson chisquare tests for categorical variables were performed to test the statistical differences among groups. Cochran-Armitage trend tests were applied in order to identify significant differences across BMI groups. Regression models were used to generate unadjusted odds ratios and adjusted odds ratios, including 95% confidence intervals, for all outcomes using the participants with normal BMI (18.5 to 24.9 kg/m2) as the reference group. Logistic regression models generated odds ratios that provide a valid estimate of the relative risk when the incidence is smaller than 10%; however, the results are still displayed as odds ratios in the tables.
25.
Potential confounders controlled for in the adjusted odds ratio regression models included maternal age, parity, smoking during pregnancy, neighbourhood education quartiles, and neighbourhood mean family income quartiles. We used SAS version 9.2 (SAS Institute Inc., Cary NC) software for statistical analysis.BORN Ontario is a registry prescribed under the Personal Health Information Protection Act, 2004. Registry status affords BORN the authority to collect, use, and disclose personal health information without consent for the purpose of enhancing health care in Ontario. Thus, no consent from the women in this cohort was required for the use of these data for research purposes.
Ethics approval of the study was provided prior to data analysis by The Ottawa Hospital Research Ethics Board.
RESULTS
A total of 6674 records with complete pre-pregnancy BMI information were identified from the database. The sample included 3698 (55.4%) women with normal BMI, 1648(24.7%) overweight women, 786 (11.8%) women in obese class I, 288 (4.3%) women in obese class II, and 254 (3.8%) women in obese class III. Maternal characteristics are shown in Table 1. Statistically significant differences were noted between BMI groups for rates of pre-gestational diabetes, hypertension, and asthma, with the highest rates noted for obese categories. Neighbourhood education and family income tended to be lower on average in women with higher BMI.
Table 1Characteristics of the 6674 women according to BMI
| Variable | Normal (n = 3698) n (%) | Overweight (n = 1648) n (%) | Obese class I (n = 786) n (%) | Obese class II (n = 288) n (%) | Obese class III (n = 254) n (%) | P |
|---|---|---|---|---|---|---|
| Maternal age, years | 0.060 | |||||
| ≤20 | 116 (3.1) | 35 (2.1) | 16 (2.0) | 5 (1.7) | 5 (1.7) | |
| 21 to 34 | 2423 (65.5) | 1121 (68.0) | 550 (70.0) | 206 (71.5) | 173 (68.1) | |
| ≤ 35 | 1159 (31.3) | 492 (29.9) | 220 (28.0) | 77 (26.7) | 76 (29.9) | |
| BMI, mean ± SD | 21.9 ± 1.75 | 27 2 ± 1 39 | 32 1 ± 1 42 | 37 1 ± 1 35 | 45 9 ± 5 72 | < 0.001 |
| Parity | < 0.001 | |||||
| 0 | 1755 (47.5) | 691 (41.9) | 301 (38.3) | 113 (39.2) | 106 (41.7) | |
| ≥ 1 | 1943 (52.5) | 957 (58.1) | 485 (61.7) | 175 (60.8) | 148 (58.3) | |
| Pregestational diabetes | < 0 001 | |||||
| No | 3656 (99.1) | 1617 (98.3) | 759 (96.8) | 276 (96.2) | 247 (97.2) | |
| Yes | 34 (0.9) | 28 (1.7) | 25 (3.2) | 11 (3.8) | 7 (2.8) | |
| Missing | 8 (0.2) | 3 (0.2) | 2 (0.3) | 1 (0.3) | 0 (0) | |
| Chronic hypertension | < 0 001 | |||||
| No | 3659 (99.2) | 1672 (98.9) | 762 (97.2) | 264 (92.0) | 227 (89.4) | |
| Yes | 31 (0.8) | 18 (1.1) | 22 (2.8) | 23 (8.0) | 27 (10.6) | |
| Missing | 0 (0) | 3 (0.2) | 2 (0.3) | 1 (0.3) | 0 (0) | |
| Asthma | < 0 001 | |||||
| No | 3483 (94.4) | 1517 (92.2) | 717 (91.5) | 256 (89.2) | 225 (88.6) | |
| Yes | 207 (5.6) | 128 (7.8) | 67 (8.9) | 31 (10.8) | 29 (11.4) | |
| Missing | 8 (0.2) | 3 (0.2) | 2 (0.3) | 1 (0.3) | 0 (0) | |
| Smoking in pregnancy | 0 077 | |||||
| No | 3463 (93.9) | 1532 (93.1) | 721 (91.7) | 260 (90.6) | 234 (92.5) | |
| Yes | 227 (6.2) | 113 (6.9) | 65 (8.3) | 27 (9.4) | 19 (7.5) | |
| Missing | 8 (0.2) | 3 (0.2) | 0 (0) | 1 (0.3) | 1 (0.4) | |
| Education quartiles | < 0 001 | |||||
| 1 (Lowest) | 700 (20.4) | 377 (24.6) | 204 (28.1) | 96 (36.1) | 93 (38.3) | |
| 2 | 863 (25.1) | 370 (24.1) | 202 (27.9) | 81 (30.5) | 59 (24.3) | |
| 3 | 909 (26.4) | 402 (26.2) | 178 (24.6) | 52 (19.6) | 56 (23.1) | |
| 4 (Highest) | 968 (28.1) | 386 (25.2) | 141 (19.5) | 37 (13.9) | 35 (14.4) | |
| Missing | 258 (7) | 113 (6.9) | 61 (7.8) | 22 (7.6) | 11 (4.3) | |
| Family income quartiles | < 0 001 | |||||
| 1 (Lowest) | 760 (22.1) | 381 (24.8) | 221 (30.5) | 88 (33.1) | 79 (32.5) | |
| 2 | 834 (24.2) | 382 (24.9) | 180 (24.8) | 73 (27.4) | 65 (26.8) | |
| 3 | 902 (26.2) | 413 (26.9) | 166 (22.9) | 53 (19.9) | 59 (24.3) | |
| 4 (Highest) | 944 (27.4) | 395 (23.4) | 158 (21.8) | 52 (19.6) | 40 (16.5) | |
| Missing | 258 (7.0) | 113 (6.9) | 61 (7.8) | 22 (7.6) | 11 (4.3) | |
| Rural area | 285 (7.72) | 164 (9.96) | 74 (9.44) | 36 (12.50) | 43 (16.93) | |
| Urban area | 3407 (92.28) | 1482 (90.04) | 710 (90.56) | 252 (87.50) | 211 (83.07) | |
| Missing | 8 (0.002) | 2(0.001) | 2 (0.002) | 0 (0) | 0 (0) |
The unadjusted and adjusted odds ratios for pregnancy outcomes are shown in Table 2. Rates of preeclampsia and gestational diabetes increased as BMI increased (P < 0.001), with results remaining significant after adjusting for potential confounders. Overweight and obese (class I/II/III) women had a significantly higher likelihood of having gestational hypertension, with the highest rates observed in obese class II; the trend test was significant across categories, but a clear linear relationship between hypertension and BMI was not observed. Lower rates of preterm labour were observed in overweight and obese women; however, the association was only statistically significant in overweight and class I obese women. A significant difference was not found for rates of PROM and PPROM across BMI categories.
Table 2Association between adverse pregnancy outcomes and maternal BMI
| Outcome | Normal (n = 3698) Missing = 9 | Overweight (n = 1646) Missing = 2 | Obese class I (n = 784) Missing = 2 | Obese class II (n = 287) Missing = 1 | Obese class III (n = 253) Missing = 1 |
|---|---|---|---|---|---|
| Preeclampsia | |||||
| n (%) | 101 (2.7) | 71 (4.3) | 36 (4.6) | 17 (5.9) | 30 (11.9) |
| OR (95% CI) | 1.00 | 1.60 (1.17 to 2.18) | 1.71 (1.16 to 2.52) | 2.24 (1.32 to 3.79) | 4.78 (3.11 to 7.34) |
| aOR (95% CI) | 1.00 | 1.74 (1.25 to 2.41) | 1.91 (1.27 to 2.90) | 2.48 (1.42 to 4.32) | 5.19 (3.32 to 8.13) |
| Gestational hypertension | |||||
| n (%) | 86 (2.3) | 60 (3.7) | 49 (6.3) | 26 (9.1) | 22 (8.7) |
| OR (95% CI) | 1.00 | 1.55 (1.13 to 2.22) | 2.79 (1.95 to 4.00) | 4.17 (2.64 to 6.59) | 3.99 (2.45 to 6.49) |
| aOR (95% CI) | 1.00 | 1.68 (1.18 to 2.38) | 3.07 (2.10 to 4.49) | 4.80 (3.00 to 7.70) | 3.72 (2.22 to 6.25) |
| Gestational diabetes | |||||
| n (%) | 96 (2.6) | 81 (4.9) | 59 (7.5) | 32 (11.2) | 37 (14.6) |
| OR (95% CI) | 1.00 | 1.89 (1.42 to 2.53) | 2.89 (2.11 to 3.96) | 4.28 (2.93 to 6.28) | 5.62 (3.93 to 8.03) |
| aOR (95% CI) | 1.00 | 1.82 (1.33 to 2.49) | 2.84 (2.00 to 4.02) | 4.04 (2.57 to 6.35) | 5.70 (3.73 to 8.70) |
| PROM | |||||
| n (%) | 135 (3.7) | 71 (4.3) | 22 (2.8) | 5 (1.7) | 6 (2.4) |
| OR (95% CI) | 1.00 | 1.19 (0.89 to 1.59) | 0.76 (0.48 to 1.20) | 0.47 (0.19 to 1.15) | 0.64 (0.28 to 1.46) |
| aOR (95% CI) | 1.00 | 1.31 (0.96 to 1.77) | 0.88 (0.55 to 1.41) | 0.56 (0.22 to 1.38) | 0.60 (0.24 to 1.48) |
| PPROM | |||||
| n (%) | 120 (3.3) | 58 (3.5) | 27 (3.4) | 13 (4.5) | 8 (3.2) |
| OR (95% CI) | 1.00 | 1.08 (0.79 to 1.49) | 1.06 (0.69 to 1.62) | 1.41 (0.79 to 2.53) | 0.97 (0.47 to 2.01) |
| aOR (95% CI) | 1.00 | 1.07 (0.76 to 1.49) | 0.96 (0.61 to 1.50) | 1.28 (0.69 to 2.36) | 0.90 (0.43 to 1.89) |
| Preterm labour | |||||
| n (%) | 180 (4.9) | 43 (2.6) | 25 (3.2) | 12 (4.2) | 10 (4.0) |
| OR (95% CI) | 1.00 | 0.52 (0.37 to 0.73) | 0.64 (0.42 to 0.97) | 0.85 (0.47 to 1.55) | 0.80 (0.42 to 1.54) |
| aOR (95% CI) | 1.00 | 0.51 (0.36 to 0.73) | 0.61 (0.39 to 0.96) | 0.75 (0.40 to 1.40) | 0.75 (0.39 to 1.45) |
* P < 0.001 with Cochran-Armitage trend test.
† Adjusted for maternal age, parity, smoking, education quintiles, and family income quintiles.
Obesity was associated with a decreased rate of vaginal delivery: the rate in women with normal BMI was 59.9%, versus 46.3% in class III obese women (aOR 0.76; 95% CI 0.67 to 0.87) (Table 3). There was also a decreased rate of assisted vaginal delivery in overweight and obese women, with a significant downward trend (P < 0.001); however, there was no linear relationship with rates of assisted delivery across the overweight/obesity groups. In examining this further, rates of both emergency and elective CS were found to increase with BMI (obese class III aOR 1.32 for emergency CS and 1.64 for elective CS; P < 0.001), both in a linear fashion. When Caesarean sections were examined by primary and repeat categories, overweight/obese women who had not had a previous CS were at an increased risk for CS in their current pregnancy (obese class III aOR 1.46); increasing BMI was not associated with an increased risk of repeat CS.
Table 3Association between mode of delivery and maternal BMI
| Outcome | Normal | Overweight | Obese class I | Obese class II | Obese class III |
|---|---|---|---|---|---|
| Mode of delivery | |||||
| Vaginal | |||||
| Total n (missing) | 3689 (9) | 1644 (4) | 784 (2) | 288 (0) | 253 (1) |
| n (%) | 2210 (59.9) | 906 (55.1) | 404 (51.5) | 132 (45.8) | 117 (46.3) |
| OR (95% CI) | 1.00 | 0.92 (0.87 to 0.97) | 0.86 (0.80 to 0.93) | 0.77 (0.67 to 0.87) | 0.77 (0.67 to 0.88) |
| aOR (95% CI) | 1.00 | 0.92 (0.87 to 0.97) | 0.84 (0.78 to 0.90) | 0.76 (0.67 to 0.87) | 0.76 (0.67 to 0.87) |
| Assisted vaginal | |||||
| Total n (missing) | 3689 (9) | 1644 (4) | 784 (2) | 288 (0) | 253 (1) |
| n (%) | 332 (9.0) | 123 (7.5) | 40 (5.1) | 18 (6.3) | 11 (4.4) |
| OR (95% CI) | 1.00 | 0.82 (0.66 to 1.01) | 0.54 (0.39 to 0.76) | 0.67 (0.41 to 1.10) | 0.46 (0.25 to 0.85) |
| aOR (95% CI) | 1.00 | 0.85 (0.67 to 1.07) | 0.59 (0.41 to 0.85) | 0.80 (0.48 to 1.34) | 0.52 (0.28 to 0.97) |
| Caesarean section | |||||
| Total n (missing) | 3696 (2) | 1647 (1) | 786 (0) | 288 (0) | 254 (0) |
| n (%) | 1149 (31.1) | 616 (37.4) | 341 (43.4) | 138 (47.9) | 126 (49.6) |
| OR (95% CI) | 1.00 | 1.20 (1.11 to 1.30) | 1.39 (1.27 to 1.53) | 1.54 (1.35 to 1.75) | 1.59 (1.40 to 1.82) |
| aOR (95% CI) | 1.00 | 1.20 (1.10 to 1.30) | 1.41 (1.27 to 1.54) | 1.50 (1.31 to 1.72) | 1.49 (1.30 to 1.70) |
| Caesarean section | |||||
| Elective CS | |||||
| Total n (missing) | 3696 (2) | 1647 (1) | 786 (0) | 288 (0) | 254 (0) |
| n (%) | 523 (14.2) | 307 (18.6) | 166 (21.1) | 71 (24.7) | 67 (26.4) |
| OR (95% CI) | 1.00 | 1.32 (1.15 to 1.50) | 1.49 (1.28 to 1.75) | 1.74 (1.40 to 2.16) | 1.86 (1.50 to 2.32) |
| aOR (95% CI) | 1.00 | 1.23 (1.09 to 1.40) | 1.40 (1.19 to 1.64) | 1.63 (1.31 to 2.02) | 1.64 (1.31 to 2.04) |
| Emergency CS | |||||
| Total n (missing) | 3696 (2) | 1647 (1) | 786 (0) | 288 (0) | 254 (0) |
| n (%) | 626 (16.9) | 307 (18.6) | 175 (22.3) | 67 (23.3) | 57 (22.4) |
| OR (95% CI) | 1.00 | 1.10 (0.97 to 1.25) | 1.31 (1.13 to 1.53) | 1.37 (1.10 to 1.71) | 1.32 (1.04 to 1.68) |
| aOR (95% CI) | 1.00 | 1.16 (1.03 to 1.31) | 1.45 (1.26 to 1.67) | 1.40 (1.13 to 1.75) | 1.32 (1.06 to 1.65) |
| Primary CS | |||||
| Total n (missing) | 3209 (2) | 1339 (1) | 616 (0) | 215 (0) | 196 (0) |
| n (%) | 708 (22.1) | 339 (25.3) | 180 (29.2) | 66 (30.7) | 71 (36.2) |
| OR (95% CI) | 1.00 | 1.15 (1.03 to 1.28) | 1.32 (1.15 to 1.52) | 1.39 (1.13 to 1.72) | 1.64 (1.35 to 2.00) |
| aOR (95% CI) | 1.00 | 1.16 (1.04 to 1.29) | 1.35 (1.19 to 1.53) | 1.38 (1.13 to 1.67) | 1.46 (1.23 to 1.73) |
| Previous CS | |||||
| Total n (missing) | 486 (0) | 306 (0) | 170 (0) | 73 (0) | 58 (0) |
| n (%) | 442 (91.0) | 276 (90.2) | 161 (94.7) | 72 (98.6) | 55 (94.8) |
| OR (95% CI) | 1.00 | 0.99 (0.95 to 1.04) | 1.04 (1.00 to 1.09) | 1.08 (1.04 to 1.13) | 1.04 (0.98 to 1.11) |
| aOR (95% CI) | 1.00 | 0.99 (0.94 to 1.04) | 1.03 (0.97 to 1.09) | 1.07 (1.00 to 1.15) | 1.03 (0.95 go 1.12) |
* P < 0.001 with Cochran-Armitage trend test.
† Adjusted for maternal age, parity, smoking, education quintiles, and family income quintiles.
Intrapartum outcomes are presented in Table 4. Increasing BMI was associated in linear fashion with the need for induction of labour (obese class III aOR = 1.67). However, rates of labour augmentation were similar across BMI groups; results are shown in Table 4 for those whose information on labour augmentation was recorded.
Table 4Association between intrapartum outcome and maternal BMI
| Outcome variable | Normal | Overweight | Obese class I | Obese class II | Obese class III |
|---|---|---|---|---|---|
| Labour | |||||
| Spontaneous labour | |||||
| Total n | 3698 | 1648 | 786 | 288 | 254 |
| n (%) | 2218 (60.0) | 871 (52.9) | 379 (48.2) | 101 (35.1) | 75 (29.5) |
| OR (95% CI) | 1.00 | 0.88 (0.81 to 0.93) | 0.80 (0.74 to 0.87) | 0.58 (0.50 to 0.69) | 0.49 (0.41 to 0.60) |
| aOR (95% CI) | 1.00 | 0.88 (0.83 to 0.93) | 0.81 (0.75 to 0.87) | 0.55 (0.46 to 0.66) | 0.52 (0.43 to 0.63) |
| Induction of labour | |||||
| Total n | 3698 | 1648 | 786 | 288 | 254 |
| n (%) | 937 (25.3) | 463 (28.1) | 241 (30.7) | 109 (37.9) | 109 (42.9) |
| OR (95% CI) | 1.00 | 1.11 (1.01 to 1.22) | 1.21 (1.07 to 1.36) | 1.49 (1.28 to 1.75) | 1.69 (1.45 to 1.97) |
| aOR (95% CI) | 1.00 | 1.16 (1.05 to 1.27) | 1.29 (1.15 to 1.46) | 1.62 (1.39 to 1.88) | 1.67 (1.43 to 1.93) |
| Augmentation of labour | |||||
| Total n (missing) | 2208 (10) | 869 (2) | 374 (5) | 101 (0) | 75 (0) |
| n (%) | 1415 (64.1) | 548 (63.1) | 230 (61.5) | 57 (56.4) | 45 (60.0) |
| OR (95% CI) | 1.00 | 0.98 (0.93 to 1.04) | 0.96 (0.88 to 1.05) | 0.88 (0.74 to 1.05) | 0.94 (0.78 to 1.13) |
| aOR (95% CI) | 1.00 | 1.01 (0.95 to 1.07) | 1.00 (0.91 to 1.07) | 0.86 (0.71 to 1.04) | 0.96 (0.80 to 1.14) |
| Length of second stage | |||||
| Second stage > 3 hr | |||||
| Total n (missing) | 2534 (12) | 1023 (8) | 441 (4) | 150 (0) | 128 (0) |
| n (%) | 279 (11.0) | 120 (11.7) | 38 (8.6) | 17 (11.3) | 11 (8.6) |
| OR (95% CI) | 1.00 | 1.07 (0.87 to 1.30) | 0.78 (0.57 to 1.08) | 1.03 (0.65 to 1.63) | 0.78 (0.44 to 1.39) |
| aOR (95% CI) | 1.00 | 1.14 (0.93 to 1.38) | 0.95 (0.70 to 1.31) | 1.25 (0.81 to 1.94) | 0.93 (0.54 to 1.61) |
| Labour analgesia | |||||
| Spinal | |||||
| Total n (missing) | 3695 (3) | 1648 (0) | 786 (0) | 288 (0) | 254 (0) |
| n (%) | 747 (20.2) | 407 (24.7) | 225 (28.6) | 92 (31.9) | 77 (30.3) |
| OR (95% CI) | 1.00 | 1.22 (1.10 to 1.36) | 1.42 (1.25 to 1.61) | 1.58 (1.32 to 1.89) | 1.50 (1.23 to 1.83) |
| aOR (95% CI) | 1.00 | 1.19 (1.07 to 1.32) | 1.36 (1.19 to 1.54) | 1.47 (1.22 to 1.77) | 1.36 (1.11 to 1.66) |
| Epidural | |||||
| Total n (missing) | 3695 (3) | 1648 (0) | 786 (0) | 288 (0) | 254 (0) |
| n (%)* | 2177 (58.9) | 908 (55.1) | 409 (52.0) | 146 (50.7) | 132 (52.0) |
| OR (95% CI) | 1.00 | 0.94 (0.89 to 0.98) | 0.88 (0.82 to 0.95) | 0.86 (0.77 to 0.97) | 0.88 (0.78 to 1.00) |
| aOR (95% CI) | 1.00 | 0.95 (0.91 to 1.00) | 0.91 (0.85 to 0.98) | 0.95 (0.85 to 1.06) | 0.91 (0.81 to 1.02) |
| General anaesthesia | |||||
| Total n (missing) | 3695 (3) | 1648 (0) | 786 (0) | 542 (0) | |
| n (%) | 42 (1.1) | 29 (1.8) | 12 (1.5) | 8 (1.5) | |
| OR (95% CI) | 1.00 | 1.56 (0.97 to 2.51) | 1.35 (0.71 to 2.57) | 1.30 (0.61 to 2.75) | |
| aOR (95% CI) | 1.00 | 1.55 (0.96 to 2.51) | 1.12 (0.56 to 2.26) | 1.24 (0.58 to 2.63) | |
* P < 0.001 with Cochran-Armitage trend test.
† Adjusted for maternal age, parity, smoking, education quintiles, and family income quintiles.
‡ The number of general anaesthesia for obese class II was not reported because the cell count was < 5; obese class II and obese class III were modelled as one group.
There was no significant difference observed across BMI categories for a prolonged second stage of labour (defined as > 3 hours). Further, no trends or significant differences were observed when data were stratified to compare primiparous with multiparous patients, with or without epidural analgesia (data not shown).
There was a statistically significant trend demonstrating an increase in use of spinal analgesia with increasing BMI. Consequently, overweight and obese women had lower rates of epidural analgesia.
DISCUSSION
The results of this retrospective cohort study demonstrated that women with overweight or obese BMI had a higher rate of pre-existing morbidities such as diabetes and chronic hypertension that affected their pregnancy and delivery outcomes negatively. Maternal overweight and obesity were linearly associated with higher rates of preeclampsia and gestational diabetes. Gestational hypertension also increased significantly with increasing BMI category, although the highest rate was observed in class II obesity. Women with BMI > 25 were also more likely to require induction of labour, with subsequent decreased rates of vaginal delivery and operative vaginal delivery, and increased rates of both elective and emergency CS. Rates of elective CS increased in parallel to increasing BMI. No differences were noted across BMI groups in the rates of augmentation of labour or length of the second stage of labour.
Higher rates of preeclampsia, gestational hypertension, and gestational diabetes have been well documented in obese populations.
8.
,26.
,27.
However, the linear relationships we observed in stratification across increasing BMI categories are important findings. Conflicting results have been reported on the association of obesity with preterm labour, with some studies reporting a significant decrease in preterm delivery in obese populations27.
, 28.
, 29.
and others reporting an increased risk.30.
,31.
Additionally, several studies have reported no association between obesity and preterm delivery.5.
,32.
, 33.
, 34.
The results of our study offer a potential explanation for the conflicting evidence found in previous reports. Because our analysis used a more nuanced separation of BMI categories, our results indicated that although overweight and obese class I women were less likely to experience preterm labour, rates of preterm labour for women in class II and class III obesity categories were similar to those of normal weight women.The higher rates of preeclampsia, hypertension, and diabetes that were found in overweight and obese women in our study may have contributed to the increased rates of induction of labour found in women in the same groups; several studies have reported that these factors may all contribute to adverse maternal and fetal outcomes if not addressed prior to the onset of spontaneous labour.
35.
, 36.
, 37.
Induction of labour has been acknowledged as leading to higher rates of operative vaginal delivery or CS.38.
,39.
Furthermore, numerous studies have associated obesity in pregnancy with higher rates of CS.5.
,7.
,32.
,40.
, 41.
, 42.
, 43.
, 44.
, 45.
, 46.
This is consistent with our finding that rates of CS increased in parallel with increasing BMI. The underlying mechanism leading to increased CS rates in obese patients remains unclear, but decreased uterine contractility47.
and higher rates of induction of labour in obese women may contribute.39.
Further, our finding of increased rates of CS in overweight and obese women may be due in part to inadequate doses of medication given to augment labour, as augmentation protocols do not take variations in BMI into account. Increased rates of CS were found only in women undergoing primary CS, as opposed to repeat CS. Extrapolating from these results and other published data, it appears that rates of CS are highest in obese nulliparous women.32.
,40.
,48.
, 49.
, 50.
, 51.
Despite the fact that increased adverse outcomes have been associated with surgical intervention in obese patients,52.
, 53.
, 54.
rates of elective CS were found to increase across BMI categories in our study. Increased rates of elective CS were likely due to adverse maternal outcomes, fetal macrosomia, or a scheduled repeat CS. Obstetricians may also be reluctant to perform operative vaginal delivery in obese women given the increased risk of shoulder dystocia due to fetal macrosomia, which is more common in obese mothers.55.
,56.
In a recent study by Fyfe et al., obese nulliparous women were found to have a higher rate of CS in the first, but not the second, stage of labour.
50.
This may explain our finding that overweight and obese women did not have a longer second stage of labour than women with normal BMI. Our results thus support the conclusion that progress in labour is similar for all BMI groups beyond the first stage of labour. The results indicated an increase in the use of regional anaesthesia with increasing BMI. This may be attributed to the higher rate of CS in overweight and obese women, as regional anaesthesia is preferred for this procedure.A chief strength of our study is the classification of outcomes based on WHO BMI categorization; pooling women into more general “overweight” and “obese” categories tends to be more common in the literature, and does not offer as nuanced an interpretation of the impact of increasing BMI on maternal outcomes.
8.
,41.
,49.
Our study also had adequate sample sizes across each BMI category, likely due to the high number of referrals of obese women to the tertiary care clinic from which our population sample was drawn.Information collected retrospectively from databases may have limited reliability. The quality of data in our study was likely reasonably high, given that BORN Ontario undergoes extensive routine data quality audits.
22.
Pre-pregnancy BMI was used to classify women in the study, as it is generally accepted. However, this weight is usually self-reported and may not be accurate. Other limitations of the dataset included difficulty establishing whether Caesarean sections occurred in the first or second stage of labour and a referral bias in the participant sample, because women referred to the study clinic generally have higher rates of comorbidities including obesity. The control population used in the study received care at a tertiary centre, and therefore also had, on average, more complex medical issues than would a general patient population found in a community setting. Finally, because the population sample came from a tertiary care clinic with protocols in place to enhance the care of overweight and obese pregnant women, rates of certain adverse outcomes may have been under-represented. Using the Cochrane-Armitage trend test allowed us to show a significant relationship between specific outcomes and different BMI classes; however, it is important to note that although the test reached statistical significance for certain categories, this was not a reflection of the numbers seen in some of the results for gestational hypertension, assisted vaginal delivery, emergency CS, and spinal and epidural analgesia.Maternal obesity contributes significantly to a poorer prognosis for mother and baby during delivery and in the immediate postpartum period. This study assessed extensively the relationship of obesity to maternal outcomes, and demonstrated the higher antenatal and perinatal risks that overweight and obese mothers face. Clinical guidelines from Canada
57.
and the United States58.
,59.
clinical guidelines for the management of obese pregnant women and public health interventions for obese mothers and their infants have been developed and implemented in a variety of settings worldwide. Interventions directed at weight loss and prevention of excessive weight gain must begin in the pre-conception period, and must include counselling by obstetrical care providers regarding the risks and complications conferred by obesity. Future directions of this research will involve reviewing the postpartum outcomes of this patient population and their impact on hospital cost and health care utilization. Long-term studies involving the implementation of nutrition and diet programs in high-risk patient populations are also needed to help ensure improvement of obstetric and neonatal outcomes.This retrospective study of a Canadian population of obese pregnant women shows a significant increase in the incidence of significant pregnancy complications such as preeclampsia, gestational diabetes, and hypertension. Pregnant women with an elevated BMI also had a higher rate of induction of labour than women with normal BMI, likely as a result of these complications. The delivery outcome translates into an increased rate of Caesarean section in these women, and this can have a significant effect on their postpartum course and on future pregnancies.
ACKNOWLEDGEMENTS
The authors acknowledge the support provided by Dr Ann Sprague from BORN Ontario. The authors would also like to acknowledge the contributions to data entry and literature review to this project by Linda McCabe, Liam Faught, and Karine Tawagi.
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Article info
Publication history
Accepted:
September 12,
2012
Received:
February 28,
2012
Footnotes
The preliminary results of this study were presented at the Society of Maternal Fetal Medicine’s 30th Annual Scientific Meeting in Chicago, Illinois on February 5, 2010.
The final results of this study were presented at the Annual Clinical Meeting of The Society of Obstetricians and Gynaecologists of Canada in Vancouver, British Columbia, June 21-25, 2011.
Competing Interests: None declared
Identification
Copyright
© 2013 Society of Obstetricians and Gynaecologists of Canada. Published by Elsevier Inc. All rights reserved.
