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Keywords:

  • maternal obesity;
  • intrapartum;
  • intervention;
  • labor induction;
  • labor augmentation;
  • cesarean birth;
  • labor dystocia

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONCLUSION
  8. CONFLICT OF INTEREST
  9. REFERENCES
  10. Biographies

Introduction

The objective of this systematic review was to determine the current state of knowledge about intrapartum management associated with obesity in healthy nulliparous women. Nulliparous obese women are at higher risk for unplanned cesarean birth when compared with their normal-weight counterparts, and much of this increased risk is associated with labor management differences. There is a need to better understand the differences in intrapartum management of nulliparous women who are obese.

Methods

The PubMed, CINAHL, EBSCO, Google Scholar, and MEDLINE databases were searched in August 2012, with identified studies then assessed for applicability and quality. Eight studies were retained for the review.

Results

Intrapartum interventions used significantly more often for healthy, obese nulliparous women when compared with normal-weight women were induction of labor, augmentation of labor, and cesarean birth. It is unclear if assisted vaginal birth occurs more frequently among obese women. Epidural anesthesia, artificial rupture of membranes prior to 6 cm of cervical dilation, and early hospital admission were shown in separate studies to be used more often in obese women. Intrapartum interventions were used more frequently in obese women in a dose-dependent manner by body mass index.

Discussion

Future studies examining the intrapartum management of obese nulliparous women are needed with: 1) samples defined by standardized obesity classifications; 2) further analysis of diverse intrapartum interventions; and 3) prospective, randomized designs to allow for causality conclusions linking intrapartum intervention use to an obese woman's risk for cesarean birth. Implications for clinical practice from this systematic review are that healthy, nulliparous obese women are exposed to common intrapartum interventions more often than normal-weight women. In the absence of evidence on the use of appropriate use of intrapartum interventions in this population, health care providers should carefully monitor management choices when working with healthy, nulliparous obese women.


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONCLUSION
  8. CONFLICT OF INTEREST
  9. REFERENCES
  10. Biographies

The United States is in the midst of an obesity epidemic, with nearly two-thirds of US women of childbearing age either overweight (body mass index [BMI] = 25-29.9 kg/m2) or obese (BMI ≥ 30 kg/m2).[1] This obesity epidemic has developed quickly over the past 20 years, resulting in a very different BMI mix of women becoming pregnant now than in the near past.[2] The purpose of this systematic review was to examine evidence on the use of intrapartum interventions in healthy, nulliparous obese women.

Clinical investigators have shown that obese women are at increased risk for unplanned cesarean birth when compared with normal-weight women, thus contributing disproportionately to the nationwide cesarean rate.[3-9] The United States has seen a dramatic increase of more than 60% in the nation's cesarean birth rate since 1996.[10] Currently, the US cesarean rate is at an all-time high of 32.8%.[11] When obese women have cesarean birth, they are more likely than their normal-weight counterparts to experience significant morbidity and mortality following birth.[12-15] Postoperative infection, clotting disorders, postpartum hemorrhage, and prolonged hospitalization have all been found to occur more frequently after cesarean birth among obese women when compared with normal-weight women. Up to a third of maternal deaths in pregnancy are associated with obesity complications,[12] a statistic that is of key importance in the United States, where the national maternity mortality rate is on the rise and currently ranks 48th in the world.[16]

Nulliparous obese women are at the highest risk for unplanned cesarean birth. In a 2008 meta-analysis of 11 studies, Poobalan et al found that nulliparous obese women's risk of cesarean birth was more than double that of normal-weight women (odds ratio [OR], 2.26; 95% confidence interval [CI], 2.04-2.51), whereas morbidly obese (BMI > 35 kg/m2) women's risk was more than triple that of normal-weight women (OR, 3.38; 95% CI, 2.49-4.57).[8] Nulliparous obese women are at highest risk for unplanned cesarean birth in part because they undergo labor induction more frequently than are multiparous, obese women[17] and are more likely to have a failed induction.[18] However, the primary reason that obese nulliparous women are at highest risk for cesarean birth and intrapartum interventions to speed labor is slow labor progress. In a large, multicenter study of contemporary labor practices from 2011, nulliparous women with a BMI less than 25 kg/m2 completed labor 2 hours faster than obese women and 4 hours faster than morbidly obese women (BMI > 40 kg/m2).[17] Moreover, obese nulliparous women were found to lack acceleration of cervical progress in the active phase of labor.[19]

Abnormally slow progress in labor is known as labor dystocia.[7, 19-22] Labor dystocia was last defined by the American College of Obstetricians and Gynecologists in 2003 as “an abnormal labor that results from…abnormalities of the power, the passenger, or the passage” after “women…enter the active phase when cervical dilation is between 3 cm and 4 cm.”[23] Although labor dystocia among obese women was initially thought to be caused by soft-tissue obstruction in late labor and at birth,[5] recent studies have found that obese women's labors are slower during the first stage, from 4 to 10 cm of cervical dilation.[7, 24-26] Once obese women reach the second stage of labor, the vaginal birth rate for them is the same as it is for normal-weight women.[27, 28]

Quick Points

  • Nearly two-thirds of women of childbearing age in the United States are currently either obese or overweight.
  • Obese nulliparous women are more likely than normal-weight women to have an unplanned cesarean birth.
  • Obese nulliparous women are more likely than normal-weight women to have intrapartum interventions intended to initiate and speed their labors.
  • More studies are needed to evaluate the timing and use of intrapartum interventions and their efficacy in managing the labors of nulliparous obese women.

Obese women are more likely than normal-weight women to have slightly larger neonates, yet in studies that have controlled for maternal diabetes, the higher fetal weights were not associated with additional diagnoses of labor arrest or slowing.[22, 29] It is purported that some physiology in the pregnant obese woman's system causes her myometrial cells to contract with less efficiency during the first stage of labor than is found in normal-weight women.[30-32]

Standard intrapartum management practices may compound the problem of slower labors. In a recent Canadian retrospective cohort study (N = 11,922) by Abenhaim et al that controlled for comorbidities including diabetes, preeclampsia, and gestational diabetes, increased use of intrapartum interventions such as induction of labor, early labor hospital admission, synthetic oxytocin administration, epidural anesthesia, and decreased use of assisted vaginal birth were found to explain much of the association between obesity and unplanned cesarean birth.[33] Recent literature on the problem of unplanned cesarean birth among obese women includes calls by investigators for future studies of intrapartum provider decision-making patterns that might influence labor progression and increase the likelihood of cesarean birth.[21, 24, 34, 35]

However, investigations of intrapartum intervention use in obese women have had conflicting results. Two prospective cohort studies conducted prior to the Abenhaim study did not find evidence of increased epidural usage by obese women,[26, 36] and investigators of several studies have not found there is decreased use of assisted vaginal birth among obese women.[21, 26, 27, 37-41]

Complicating the interpretation of findings from these and other studies on intrapartum management in obese women are differing study methods, sampling exclusions, and analyses. Although comorbidities, such as gestational diabetes and preeclampsia, were controlled in some studies, in others they were not. Both gestational diabetes and preeclampsia are found more frequently in obese women, in a dose-dependent relationship with maternal BMI.[21, 33, 40] When obese women have preeclampsia, they are significantly more likely to undergo induction of labor compared with other obese women without preeclampsia.[42]

In addition, induction of labor is more likely to fail when used with obese women.[18, 43, 44] In a 2011 retrospective analysis of cervical-ripening success, 53.7% of obese women had unsuccessful cervical prostaglandin ripening compared with 34.2% of normal-weight women (= .0018) following the initial attempt at cervical ripening.[44] Other investigators have found an increased risk of induction that is dose dependent by increases in maternal BMI.[18, 43] In a retrospective population cohort study of 80,887 women, women with a BMI of at least 40 kg/m2 had a 29% risk of failed induction compared with a 13% rate among normal-weight women (OR, 2.73; 95% CI, 2.53-2.96).[18] Therefore, if obese women are more likely to be induced, they are also more likely to have cesarean birth secondary to failed induction.

Maternal obesity was an independent risk factor for cesarean birth in a study that excluded all women with diabetic and hypertensive complications[35] and in a meta-analysis of 11 studies on cesarean birth in obese women that adjusted for preeclampsia and diabetes.[8] However, we found no systematic review of studies examining the association between obesity and other intrapartum interventions that controlled for medical comorbidities. Findings of studies focusing on the use of intrapartum interventions in obese women also are confounded by the lack of standardized sampling exclusions. Some studies included both nulliparous and multiparous women, others were limited to nulliparous women, and others controlled for parity via statistical analysis. The purpose of this article is to report the findings of a systematic review of studies with similar exclusions and control of confounding factors that investigated intrapartum management of healthy, obese nulliparous women.

METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONCLUSION
  8. CONFLICT OF INTEREST
  9. REFERENCES
  10. Biographies

We focused this systematic review on the question: “What intrapartum management is associated with maternal obesity in healthy nulliparous women?” Specifically, we were interested in intrapartum interventions performed before birth among these women. Intrapartum management includes medical and surgical interventions performed in the intrapartum period (from onset of labor or initiation of induction until vaginal or cesarean birth). Although comfort measures (eg, massage, hydrotherapy, repositioning, warm/ice packs) are also part of intrapartum management, no studies were found examining the use of these measures in healthy, nulliparous obese women. We also found no studies with data on intrapartum psychological support measures in obese women. We excluded studies that only analyzed cesarean birth because several meta-analyses of the use of cesareans in obese women have been published.[8, 45] Although included studies may have examined the use of cesarean birth, they also analyzed either the use of unplanned cesarean for different indications[19] or the use of other intrapartum interventions in addition to cesarean birth. Further, if the study included analysis of cesarean birth in obese women, the analysis was limited to unplanned cesarean birth (ie, cesarean birth after trial of labor). Therefore, the inclusion criteria for this review were investigation of the use of intrapartum interventions, including but not limited to unplanned cesareans, in healthy, nulliparous obese women compared with a normal-weight referent. If included studies did not limit their sample to nulliparous women, they had to either provide a separate analysis for nulliparous women or adjust for parity in the analysis.

Health in a nulliparous obese women was defined as a lack of preeclampsia. Ideally, a sample of healthy, nulliparous obese women would also exclude women with gestational diabetes, preexisting diabetes, and preexisting hypertension or control for these comorbidities in an adjusted analysis. However, gestational diabetes, preexisting diabetes, and preexisting hypertension were allowed in the studies included in this review with the rationale that in the 2012 Suidan et al study of obesity and comorbidities, although preeclampsia accounted for 44.7% of the indications for induction of labor in the group of obese women with comorbidities, other comorbidities each accounted for significantly less of the indications for induction of labor (gestational diabetes, 2.6% of the indications; chronic hypertension, 2.6%).[42] If a study did not include controls for preeclampsia, either in participant exclusion or in adjusted analysis, the study could only be included in this review if it instead controlled for induction of labor. Controlling for induction of labor would have the effect of excluding many of the more severe cases of preeclampsia.[42]

A literature search was conducted in August 2012 using the PubMed, CINAHL, EBSCO, Google Scholar, and MEDLINE databases. A university research librarian conducted a second literature search for comparison, and the results of the 2 independent searches were combined. The PubMed, CINAHL, EBSCO and MEDLINE databases were chosen to capture relevant nursing and medical literature. Google Scholar was used to help locate dissertations, conference proceedings, and book entries. Primary medical subject heading (MeSH) search terms included “obese,” “obesity,” “BMI,” “body mass index,” “body weight,” “nulliparous,” and “parity.” Primary search terms were cross-searched against secondary MeSH search terms including “management,” “intrapartum management,” “cesarean birth,” “cesarean section,” and “unplanned cesarean.” In addition, some publications were identified from the reference lists of pertinent articles.

Because of substantive changes in practice and the scope of obesity among childbearing women, publications prior to 1995 were excluded because of limited relevance to today's clinical environment. Searches were limited to human participants, original research, and the English language. Maternal age and the study's country were not restricted. Although publications from peer-reviewed journals were acceptable for inclusion, none was located that met other search criteria.

Our initial search produced 266 articles (Figure 1). These articles were reviewed in abstract form against the inclusion criteria and culled to 98 articles. Articles were excluded for being off topic, including articles that contained no information on intrapartum management, did not include obese participants, were on nonhuman populations, were not in the English language, or were not original research. Full-text copies of the remaining 98 articles were obtained through online proxies or library reserve and analyzed again for eligibility. We eliminated 90 articles because they did not include intrapartum management (n = 33), did not include obese populations (n = 12), were not available in full text (n = 5), did not control for either preeclampsia or induction (n = 8), did not provide separate analysis for nulliparous women (n = 7), or were off topic (n = 25). The remaining 8 publications were included in the review.

image

Figure 1. Flow Chart Describing Literature Extraction Process

Abbreviations: PIH, pregnancy-induced hypertension; IOL, induction of labor.

Download figure to PowerPoint

All studies were assessed for methodological quality using the Newcastle-Ottawa Scale (NOS).[46] This scale was developed to assess the quality of nonrandomized studies and involves the use of a star system to judge each study for the selection of study groups, the comparability of groups, and the method for assessing outcome of interest. The NOS has well-supported content validity and interrater reliability and has been used in many analyses of nonrandomized studies. The NOS has a maximum score of 9 stars. For the purposes of this review, studies scoring at least 6 stars were assessed as high quality.

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONCLUSION
  8. CONFLICT OF INTEREST
  9. REFERENCES
  10. Biographies

Among the 8 studies, 4 were conducted in the United States, with the remaining studies conducted in Canada, Australia, the United Kingdom, and Sweden (Table 1). Investigators examined a variety of medical and surgical interventions used in the labors of nulliparous obese women, but none included psychological support interventions or comfort measures for obese women in labor. Although investigators of 5 of the included studies limited their study population to nulliparous women, results in the remaining 3 studies either presented results separately for nulliparous women[41] or the results were adjusted for parity.[33, 47] Among the included studies, a total of 364,771 women were included for analyses.

Table 1. Study Characteristics
Study, Country,Nulliparous   Controls Included as
Years of IncludedWomen, ObesityBMI CategoriesStudy Exclusion or
BirthsNMethodologyClassification(kg/m2)Analysis Adjustment
  1. Abbreviations: BMI, body mass index; CB, cesarean birth; DM, diabetes mellitus; HTN, hypertension; IOL, induction of labor; PET, preeclampsia; TWG, total gestational weight gain.

  2. a

    Although sample included multiparous women, results reported adjusting for parity.

  3. b

    Although sample included multiparous women, separate analysis provided for nulliparous participants.

Green and Shaker (2011)[50] Australia, 2008-2009224Retrospective cohortBMI at bookingNormal = 18.5-25Obese > 35IOL (in CB calculation)
Garabedian et al (2011)[48] USA, 2004-200883,278Retrospective cross-sectionalBMI prepregnancyNormal = 18.5-24.9Overweight = 25.0-29.9Obese I = 30.0-34.9Obese II = 35.0-39.9Obese III = 40.0-49.9Morbidly obese ≥ 50AgeRace/ethnicitySmokingDMHTN/PETBirth weightGestational age at birthIOL in CB calculationAugmentation of labor
Abenhaim and Benjamin (2011)[33] Canada, 1991-200111,922aRetrospective cohortBMI at birthNormal = 20-24.9Overweight = 25-29.9Obese = 30-39.9Morbidly obese ≥ 40Maternal ageGestational ageParityPrevious CBDM or GDMIOL (in CB calculation)Birth weightCervix on admit
Cedergren (2009)[19] Sweden, 1999-2005233,887Prospective cohortBMI at first bookingNormal = 20-24.9Overweight = 25-29.9Obese I = 30-34.9Obese II = 35-39.9Morbidly obese ≥ 40IOLMaternal age
Bhattacharya et al. (2007)[40] 1976-2005UK24,241Retrospective cohortBMI prepregnancyNormal = 20-24.9Overweight = 25-29.9Obese = 30-34.9Morbidly obese ≥ 35Maternal age, heightType I DMSocial classYear of birthPETGestational HTN
Sukalich, Mingione, Glantz (2006)[47] USA, 1998-20036320a TeensRetrospective case-controlBMI prepregnancyNormal = 18.5-24.9Obese ≥ 25TWGGestational age at birthIOLDMHTNRaceParity
Vahratian et al (2005)[21] USA, 1995-2000641Prospective cohortBMI prepregnancyNormal = 19.8-26.0Overweight = 26.1-29.0 Obese > 29Maternal heightMaternal education levelTWGIOL
Jensen, Agger, Rasmussen (1999)[41] USA, 1993-19984258bRetrospective cohortBMI prepregnancyNormal = 20.0-24.9Overweight = 25.0-29.9Obese ≥ 30IOLAny pregnancy complication

All the studies included in this review scored 6 to 8 stars on the NOS (high quality). All except one[21] were retrospective cohort or case-control studies. The remaining study was a secondary analysis of a prospective study performed in North Carolina.[21] All but one[41] of the studies were published since 2005, and all but 2[33, 40] included data from women who gave birth over the course of 4 to 5 years. The Abenhaim et al study included data from Canadian women who birthed over a 10-year period at one regional hospital,[33] and the Bhattacharya et al study included data from over a 29-year period.[40] Results on the use of intrapartum interventions in the Bhattacharya et al study were adjusted for year of birth to control for changes in intrapartum practice that may have taken place over this period.

Investigators in the included studies operationalized obesity somewhat differently (Table 1). In 3 studies,[19, 33, 48] investigators classified normal BMI as 20 to 24.9 kg/m2, obesity as a BMI of 30 to 39.9 kg/m2, and morbid obesity as a BMI of at least 40 kg/m2, in keeping with World Health Organization criteria.[49] In other studies, investigators collapsed these categories to include morbidly obese women[21, 41, 47] and some overweight women[47] with the group of obese women, or counted some obese women as morbidly obese.[40] Normal BMI categories of women also differed from study to study, with 4 studies including underweight women in the group of women with normal BMIs.[21, 47, 48, 50] This confusion of obesity categories made comparisons of results from these studies problematic. Odds ratios of intrapartum intervention use in obese groups of women were computed using the normal BMI group of women as the referent.

Complicating the issue of participant grouping was the calculation of BMI at different times.[33] In 7 of the 8 studies, prepregnancy or initial booking weight and height were used to calculate BMI. Prepregnancy weight came from prenatal records at first prenatal visit or from a woman's recall of her preconception weights, a method that is cited by several investigators as consistent with actual measurements of prepregnancy weight.[51] Maternal height and weight at the time of birth were used for BMI calculations in the remaining study,[33] thereby including both prepregnancy and gestational weight gain/loss in BMI calculations. Only 2 studies controlled for maternal height in their analyses of intrapartum intervention use in healthy, nulliparous obese women.[21, 40]

Summary of Evidence

A summary of the main findings for intrapartum care associated with maternal obesity in healthy nulliparous women is in Table 2. Induction of labor, artificial rupture of membranes prior to 6 cm of cervical dilation, augmentation of labor, epidural anesthesia in labor, early hospital admission for labor, and cesarean birth were all found to be positively associated with maternal obesity in one or more of the reviewed studies.

Table 2. Review of the Literature: Intrapartum Intervention Use by BMI Category in Healthy Nulliparous Women (Normal-BMI Women as Referent)
Intrapartum InterventionStudyBMI CategoryFindings, Odds Ratio (95% CI)
  1. a

    Significance not computed, as confidence intervals overlapped.

  2. b

    Significant at P < .05.

  3. c

    ORs and CIs calculated from frequency tables provided in manuscript.

  4. d

    Significant at P < .001.

  5. e

    OR and CI not provided.

  6. f

    Not significant when adjusted for known confounders (maternal age, parity, previous cesarean birth, diabetes mellitus, gestational diabetes mellitus, hypertension, preeclampsia, cervix on admit, induction of labor, birth weight, gestational age) and for labor management differences (use of epidural analgesia, oxytocin, forceps, vacuum).

  7. g

    Adjusted risk ratio reported, not odds ratio, with rationale that the OR tends to overestimate effect when likelihood of outcome is < 10%.

Induction of laborGarabedian et al (2011)[48]OverweightObeseObese IIObese IIIBMI 40-49.9BMI ≥ 501.51 (1.42-1.60)a2.00 (1.87-2.15)2.36 (2.16-2.58)3.66 (3.30-4.01)3.51 (3.15-3.91)5.25 (3.87-7.10)
 Bhattacharya et al (2007)[40]OverweightObeseMorbidly obese1.3 (1.2-1.4)b1.8 (1.6-2.0)b1.8 (1.3-2.5)b
Artificial rupture of membranes prior to 6 cm of cervical dilationJensen, Agger, Rasmussen (1999)[41]OverweightObese1.63 (1.18-2.25)c, d1.97 (1.20-3.25)c, d
Oxytocin augmentation of laborGarabedian et al (2011)[48]OverweightObeseObese IIObese IIIBMI 40-49.9BMI ≥ 501.38 (1.28-1.49)a1.87 (1.70-2.06)2.05 (1.79-2.34)3.02 (2.57-3.55)3.00 (2.53-3.56)3.21 (1.97-5.23)
 Abenhaim and Benjamin (2011)[33]OverweightObeseMorbidly obese1.31 (1.15-1.49)d1.51 (1.31-1.75)d3.05 (1.89-4.94)d
 Vahratian (2005)[21]OverweightObeseSignificantly higher use in both categoriese
 Jensen, Agger, Rasmussen (1999)[41]OverweightObese1.59 (1.22-2.06)b, c1.98 (1.28-3.05)c, d
Epidural in laborAbenhaim and Benjamin (2011)[33]OverweightObeseMorbid lyobese1.12 (0.99-1.28)d1.11 (0.96-1.28)d1.83 (1.14-2.95)d
Assisted vaginal birthAbenhaim and Benjamin (2011)[33] For vacuum assistOverweightObeseMorbidly obese0.89 (0.70-1.13)d0.71 (0.53-0.93)d0.29 (0.09-0.93)d
 Abenhaim & Benjamin (2011)For forceps assistOverweightObeseMorbidly obese1.00 (0.81-1.24)d0.78 (0.61-0.99)d0.23 (0.07-0.73)d
 Sukalich, Mingione, Glantz (2006)[47]ObeseNot significante
 Jensen, Agger, Rasmussen (1999)[41]OverweightObese1.04 (0.76-1.43)c0.82 (0.47-1.43)c
Admission to hospital in early laborVahratian et al (2005)[21]OverweightObeseSignificantly higherin both categoriese
Unplanned cesarean birthGreen and Shaker (2011)[50]BMI >35No significant difference once IOL was adjusted fore
 Garabedian et al (2011)[48]OverweightObeseObese IIObese IIIBMI 40-49.9BMI ≥ 501.44 (1.38-1.50)d1.96 (1.86-2.06)d2.32 (2.17-2.47)d3.66 (3.39-3.95)d3.53 (3.26-3.82)d4.99 (4.00-6.22)d
 Abenhaim and Benjamin (2011)[33]OverweightObeseMorbid obese1.07 (0.80-1.43)f
 Cedergren (2009)[19] Due to obstructed laborOverweightObese IObese IIMorbid obese1.09 (0.91-1.31)1.56 (1.14-2.14)b1.33 (0.72-2.46)1.79 (0.65-4.92)
 Cedergren (2009)[19] Due to ineffective uterine contractilityOverweightObese IObese IIMorbidly obese1.50 (1.42-1.59)d2.14 (1.96-2.34)d2.72 (2.35-3.16)d3.98 (3.14-5.04)d
 Bhattacharya et al (2007)[40]OverweightObeseMorbidly obese1.5 (1.3-1.6)b2.0 (1.8-2.3)b2.8 (2.0-3.9)b
 Sukalich, Mingione, Glantz (2005)[21]Obese1.07 (1.05-1.09)b
 Vahratian (2005)[21]OverweightObese1.2 (0.8-1.8)b, g1.5 (1.05-2.0)b
 Jensen, Agger, Rasmussen (1999)[41]OverweightObese1.69 (1.06-2.68)b, c1.91 (0.94-3.86)c

Induction of labor was shown in the Garabedian et al study[48] to increase in a dose-dependent manner with maternal BMI when controlling for diabetic and hypertensive disorders and using World Health Organization BMI classifications. Although also showing a significantly increased use of induction, Bhattacharya et al[40] did not find the odds ratio for induction as high as the Garabedian et al study, especially for morbidly obese women. Geographic population differences may explain the discrepancies in findings of these 2 studies. Also, the Garabedian et al study defined morbid obesity as BMI of at least 50 kg/m2, whereas the Bhattacharya et al study defined this same category as BMI of at least 35 kg/m2.

The use of artificial rupture of membranes (AROM) prior to 6 cm of cervical dilation was significantly associated with maternal obesity when compared with normal-weight women in the Jensen et al investigation.[41] Other studies included in this review did not analyze the use of AROM.

Oxytocin augmentation of labor was used significantly more frequently among healthy, nulliparous obese women in 4 studies.[21, 33, 41, 48] Both the Garabedian et al[48] and Abenhaim et al[33] studies showed similar BMI dose-dependent increases in the use of augmentation, with levels of augmentation in morbidly obese women reaching 3 times the use in normal-weight women. Jensen et al also found increased use of augmentation in obese women, which was almost twice the rate of augmentation use in normal-weight women (OR, 1.98; 95% CI, 1.28-3.05).[41] This result was similar to the reported odds ratio in the Garabedian et al and Abenhaim et al studies.

Only one study[33] provided information about the use of epidural anesthesia. Similar to augmentation and induction of labor, epidural anesthesia was used with increasing frequency in a dose-dependent relationship to maternal BMI (Table 2).

In 2 studies, the incidence of assisted vaginal birth was lower among obese women when compared with a normal-weight cohort.[33, 41] Abenhaim et al found both that vacuum- and forceps-assisted birth occurred less frequently among obese women.[33] In contrast, Sukalich et al[47] found no difference in the use of assisted vaginal birth among obese women compared with normal-weight women.

Vahratian et al found increased use of early labor hospital admission among both overweight and obese women compared with women with normal BMI.[21] Other studies included in this analysis did not report on the use of early hospital admission in obese women.

All the investigations included in this review analyzed the use of unplanned cesarean birth in the labors of obese women (Table 2). The findings consistently demonstrated a step-wise increase in the risk of cesarean as BMI increased from overweight through obese to morbidly obese. In the only study to detail the indications for cesarean, Cedergren found that there was a highly significant increase in cesarean risk for the indication of ineffective uterine contractility, with increasing BMI but no increase in cesareans done for obstructed labor. Included studies that examined the odds ratios for unplanned cesareans in obese women varied from a low of 1.07 (95% CI, 0.80-1.43) in the Abenhaim et al study[33] to a high of 2.0 (95% CI, 1.8-2.3) in the Bhattacharya et al study.[40] This large spread in the ORs from included studies is likely a result in part of differences in sample selection and analysis. Abenhaim et al reported a nonsignificant odds ratio for unplanned cesarean use among obese women after controlling for comorbidities and various management differences, whereas the significant odds ratio results from Bhattacharya et al were obtained after controlling for only hypertensive disorders and gestational diabetes. Green et al also reported a nonsignificant odds ratio for unplanned cesarean among obese women.[50] Those investigators adjusted their analysis for induction of labor.

DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONCLUSION
  8. CONFLICT OF INTEREST
  9. REFERENCES
  10. Biographies

Results of the review of these 8 studies indicate that healthy, nulliparous obese women were more likely to receive a variety of medical and surgical interventions during labor when compared with women with normal BMIs. Intrapartum interventions used significantly more frequently among healthy, nulliparous obese women were induction of labor, augmentation of labor, and cesarean birth. It is unclear if assisted vaginal birth was used differently, and epidural anesthesia, early hospital admission, and AROM prior to 6 cm of cervical dilation were used more often among these women only in isolated studies. All the studies examining the use of intrapartum interventions in healthy, nulliparous obese women focused on the use of cesarean birth, whereas other intrapartum interventions such as epidural anesthesia, AROM, and early hospital admission were rarely considered. With the exception of 2 studies that used data from prospective cohorts,[19, 21] other studies used data from large hospital system databases or birth certificate records. Therefore, it is possible that data on the processes of intrapartum care were not available.

The practice of early labor hospital admission has been associated with an increased risk for cesarean birth,[52] epidural anesthesia,[53] and augmentation of labor in studies that have not controlled for BMI. Once women are admitted to the hospital, they are more likely to receive interventions, and their progress through labor is tracked and timed.[54] If progress is found slow or lacking, women are more likely to receive interventions intended to speed labor.[55] Especially in the setting of a healthy, nulliparous obese woman's slower labor progress, the first intrapartum intervention of hospital admission may increase her risk of other interventions. However, without more precise information on the use of early hospital admission in obese women, we are unable to comment on the relationship between early hospital admission and other interventions in this population.

Augmentation of labor occurred significantly more often among healthy, nulliparous obese women in the studies of this review. In some studies,[56, 57] augmentation with synthetic oxytocin has been found to fail more frequently in obese women when compared with normal-weight women, but in the Garabedian et al study cesarean birth was found to have a protective effect among obese women with a BMI of at least 35 kg/m2.[48] The dose of oxytocin received by obese women in the Garabedian et al study was not reported. Evidence from a 2009 prospective trial of 1273 women suggested that obese women require higher median dosages and duration of oxytocin during induction compared with normal-weight women.[58] Moreover, increased levels of cholesterol and leptin, which are more common in obese women, have been associated with decreased myometrial contractility response to synthetic oxytocin in in vitro studies.[30, 59] Currently, optimal oxytocin doses for obese women are not known. The studies included in this review did not provide information on obese women's risk for cesarean birth after augmentation. Prospective trials are needed to examine the dose, duration, and results of oxytocin augmentation in obese women to understand how use of oxytocin augmentation might change the course or outcome of obese women's labors.

Two important issues revealed in our review are that participant selection and method of BMI calculation are crucial areas for standardization in future investigations. Nulliparous women proceed through labor differently than parous women, and this is especially true for women with higher BMIs.[17] Therefore, investigations of intrapartum interventions must limit participant selection by parity or control for parity in the analysis. Many investigations were excluded for this review because they did not limit their sample by parity or analyze the confounding effect of parity. Maternal height is another important factor in women's risk for cesarean birth and other interventions in labor.[60] However, only 2 of the studies[21, 40] we reviewed controlled for maternal height when analyzing the use of intrapartum interventions among obese women.

The method of BMI calculation is another important area for standardization in future investigations. Abenhaim et al argued that BMI calculations made at the time of birth are preferable to prepregnancy BMI for the purpose of evaluating the role of labor interventions in obese women's risk for cesarean birth. Several investigations were excluded from this review because they did not limit their participants to only nulliparous women, or control for the effect of parity on their findings. Most intrapartum investigations of obese women instead consider factors such as preeclampsia as confounders that are located in time between the exposure (prepregnancy BMI) and the outcome (cesarean birth).[40, 47, 48] By using birth BMI as the exposure in their analysis, Abenhaim et al restored the traditional statistical orientation of confounder (preeclampsia) being present prior to exposure (birth BMI), which then affects the outcome (cesarean birth). Future investigations that seek to control for comorbidities through statistical analysis may want to consider using birth BMI rather than prepregnancy BMI.

Birth BMI includes both prepregnancy weight and total weight gain during pregnancy. Overweight and obese women are more likely to gain gestational weight in excess of Institute of Medicine (IOM) recommendations than are normal-weight or underweight women[61] and are more likely to have newborns who are macrosomic.[62] Although it is known that women who are obese have a higher risk for slow labor and cesarean birth independent of their gestational weight gain and fetal weight,[22] it is unknown if higher gestational weight gain among obese women puts them at increased risk for intrapartum interventions such as induction, augmentation, and epidural anesthesia. Future investigations of intrapartum intervention use for obese women may best capture the decisions made by providers if both total weight gain and prepregnancy BMI are considered in analyses.

Even in this small group of studies with the most stringent controls for comorbidities and parity, there remained large methodological differences in participant selection and analysis that limited the comparison of findings across studies. Future studies should use the IOM BMI categories so that groups of women and study results can be compared across studies. To focus on healthy obese women, women with preeclampsia, gestational diabetes, and other serious comorbidities should be analyzed separately from low-risk obese women.

This review is limited by the nonstandardized categorization of obese women in the included studies. Underweight and morbidly obese women have significantly different lengths of labor[17] and risk for cesarean birth[40] when compared with obese women. Therefore, investigations that blur the lines between these groups run the risk of reporting intervention rates and odds ratios that are difficult to compare with other investigations using standardized BMI groupings. In addition, this review is limited by all but one of the included investigations being retrospective in design. Therefore, only correlations between BMI and the use of intrapartum interventions can be made. Causality conclusions about the effect of a particular intervention on the outcomes of obese women's labors will require prospective, randomized trials.

Given that intrapartum interventions such as early hospital admission in labor,[52] epidural anesthesia,[63] and AROM[64] have been found in unselected groups of women to be associated with unplanned cesarean birth, the results of this systematic review indicate that future studies are needed to evaluate changes in maternal and neonatal outcomes when intrapartum interventions are not used or are used at different times in labor. For example, would cesarean birth be less likely in obese women if hospital admission or AROM were delayed in labor? Does this relationship change in nulliparous versus multiparous women? Does this relationship change in obese women with and without comorbidities, with and without excessive gestational weight gain? What is the optimal timing and dosage of oxytocin augmentation if used in nulliparous obese women to decrease cesarean rates? These and other questions have yet to be answered. We do know that cesarean birth in obese women results in increased morbidity and mortality.[12-14] Therefore, these and other questions relating to the intrapartum management of obese women are important to consider as new investigations are designed.

Implications for Clinical Practice

Implications for clinical practice from this systematic review are that healthy, nulliparous obese women are exposed to the common intrapartum interventions more often than are normal-weight women. There was broad consistency in the findings that healthy, nulliparous obese women are significantly more likely to experience unplanned cesarean birth and that their risk for this intervention increases in a dose-dependent manner with maternal BMI.

Providers should monitor their use of intrapartum interventions such as induction of labor, early hospital admission in labor, artificial rupture of membranes, and augmentation of labor, as these interventions are used more frequently among obese nulliparous women, and all have been shown in other studies to be associated with unplanned cesarean birth. It is unclear if these interventions are used more frequently in the labors of women who had some increased risk for cesarean before the first intervention was applied, or if the use of the intervention caused the obese woman to be more likely to end her labor with a cesarean.

With their slower rates of cervical dilation, obese women are more likely to fall outside the action line of standardized tools for labor progression[17] (ie, partogram with 2-hour action line); however, no studies have specifically examined the use of partograms with different action lines among obese women. Although augmentation of labor with synthetic oxytocin occurs more frequently in obese women's labors, correct dosages for this population are unknown. Until new studies are completed that compare birth outcomes in matched groups of obese women who are exposed to different intrapartum interventions, more liberal labor timing, and a range of synthetic oxytocin dosages, providers will have limited evidence to guide their practice with these women.

CONCLUSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONCLUSION
  8. CONFLICT OF INTEREST
  9. REFERENCES
  10. Biographies

Findings from the studies included in this review of intrapartum management of obese nulliparous women demonstrate that these women often experience labor characterized by frequent technologic interventions and unplanned cesarean birth. Although pregnant obese women are more likely to have coexisting medical complications such as diabetes and hypertension when compared with normal-weight pregnant women, obese women's risk for unplanned cesarean birth persists even when these conditions are controlled for in analyses.[33, 35, 47]

Future studies examining the intrapartum management of obese nulliparous women are needed with: 1) samples defined by standardized obesity classifications, parity, and medical comorbidities; 2) analysis of intrapartum interventions such as psychological/physical comfort measures, early hospital admission, early epidural anesthesia, AROM, and partogram use; 3) quantification of synthetic oxytocin dose requirements by maternal BMI; and 4) use of prospective, randomized designs to allow for causality conclusions about links among intrapartum interventions and a woman's risk for cesarean birth.

CONFLICT OF INTEREST

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONCLUSION
  8. CONFLICT OF INTEREST
  9. REFERENCES
  10. Biographies

The authors have no conflicts of interest to disclose.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONCLUSION
  8. CONFLICT OF INTEREST
  9. REFERENCES
  10. Biographies
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Biographies

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONCLUSION
  8. CONFLICT OF INTEREST
  9. REFERENCES
  10. Biographies
  • Nicole S. Carlson, CNM, is a doctoral student in the College of Nursing at the University of Colorado Denver. Her research is supported by the National Institute of Nursing Research at the National Institutes of Health, Award Number F31NR014061.

  • Nancy K. Lowe, CNM, PhD, FACNM, FAAN, is a professor in the College of Nursing at the University of Colorado Denver and Chair of the Division of Women, Children, and Family Health. She currently serves on the Board of Directors of the newly formed Nursing Alliance for Quality Care (NAQC), and is the Editor-in-Chief of the Journal of Obstetric, Gynecologic, and Neonatal Nursing (JOGNN).