Learning Objectives:After participating in this continuing professional development activity, the provider should be better able to:

1. Identify maternal and fetal risks associated with caring for a laboring patient with obesity.

2. Describe how biochemical differences related to obesity contribute to altered labor physiology.

3. Select evidence-based strategies to optimize induction of labor and labor management in patients with obesity.

We are all familiar with the statistics, although they are unnecessary to convey the gravity of a problem as ubiquitous as the obesity epidemic. As of 2018, over a half of pregnant women were overweight or obese [body mass index (BMI) >25].1 Approximately 28% of pregnancies are complicated by obesity, whereas 8%, nearly 1 in 10 pregnancies, are affected by class III or morbid obesity.2 From 2011 to 2015, class III obesity saw the greatest uptick in representation with a 14% increase over the 5-year period (see Table 1).1

Table 1. BMI Classification, Percent Change in Prevalence in Pregnant Patients From 2011 to 2015

Given the increasing prevalence of this clinical scenario, all obstetric providers must familiarize themselves with obesity as a medical condition and learn to communicate regarding the condition openly and without bias. The American College of Obstetricians and Gynecologists (ACOG) addresses this in a Committee Opinion regarding ethical considerations in the care of patients with obesity, noting that providers often hold implicit biases toward patients with obesity. Providers are charged with recognizing and addressing these biases, and identifying essential resources needed to optimize the care of patients with obesity.3 Ensuring exceptional care of pregnant patients with obesity further requires an understanding of the specific risks obesity poses to the maternal-fetal dyad, biochemical factors related to obesity that impact the course of labor, and evidence-based best practices for peripartum management.

Maternal and Fetal Risks Related to Obesity

With the increasing BMIs of pregnant patients came noticeable increases in many other complications including preeclampsia, gestational diabetes mellitus (GDM), operative delivery, and cesarean delivery, and fetal/neonatal risks including stillbirth, large for gestational age (LGA), shoulder dystocia, meconium aspiration, fetal distress, low Apgar scores, stillbirth, and early neonatal death.4,5 Debate arose as to whether obesity was a risk factor for these complications in and of itself, or if its confounding sequelae (ie, hypertension, diabetes, or cardiac disease) were the de facto risk factors. Suspicions of obesity as an independent risk factor were confirmed as early as 2001, when a retrospective cohort study verified the inherent "besity-attributable risk" of complications such as cesarean delivery, GDM, and LGA.2

In addition to increasing the incidence of the above comorbidities, obesity poses significant risk in the peripartum period. Studies over the past 2 decades have demonstrated prepregnancy obesity to be specifically associated with an increased need for induction of labor and related complications including failed induction, protracted labor, and failed trial of labor after cesarean delivery (TOLAC). Intrapartum management may be further confounded by disrupted intrapartum fetal monitoring and failed/repeated regional anesthesia, potentially prompting the need for general anesthesia. The postpartum patient with obesity more frequently experiences complications including postpartum hemorrhage, venous thromboembolism, and wound infection.6-12

Perhaps even more alarming, statistics have confirmed that both our patient with obesity and her fetus are at risk of not only greater morbidity, but also mortality. A recent secondary analysis of data from the Michigan Maternal Mortality review committee demonstrated that patients with obesity had 3.7 times the risk of pregnancy-related death as compared with nonobese counterparts.13 Data suggest that these patients carry an increased risk of maternal death via thromboembolism and cardiac disease.14,15 The 2004 United Kingdom's report "Why Mother's Die" identified obesity as the "greatest risk factor contributing to maternal mortality."15 Close attention to this patient population is of merit in our nation's ongoing mission to reduce maternal mortality.

Biochemical Factors

The protracting, obstructive effect of obesity on the natural course of labor was first understood experientially and described via more mechanical terms (ie, "soft tissue dystocia"). However, our initial understanding has proven a bit reductive, as the cumulative phenomenon is arguably much more complex-more biochemical than mechanical in nature. Only recently have we begun to explore the underlying pathophysiology, and recent research has identified obesity-related changes at the cellular, hormonal, and neurotransmitter levels.

A study by Zhang et al7 investigated differences in uterine contractility in pregnant patients with obesity. Samples of myometrium were obtained at the time of elective cesarean at term, and myometrium from patients with obesity was noted to contract with less amplitude (force), less frequency, and had decreased calcium flux compared with that of normal-weight women. Authors posited that dysfunctional uterine contractility may be partly responsible for the increased odds of cesarean for first-stage arrest seen in obesity.7

Several biochemical neurotransmitters and hormones have been suggested as factors in the dysfunctional labor of obesity-including leptin, cholesterol, and multiple other adipokines.10,11 Leptin is a hormone produced predominantly by adipose tissue and in smaller amounts by the placenta. Levels of leptin are directly correlated with the amount of adipose tissue present, which informs its primary function (ie, to negatively feedback on adipose formation by suppressing hunger at the level of the hypothalamus). Statistically high levels of leptin seen in obesity are known to play several different roles in labor dysfunction including desensitizing the body to the labor activation process, inhibiting apoptotic activity that normally causes amniotic membrane weakness, and inhibiting the ripening process within the term cervix.10 Finally, leptin has remarkably been coined a potential "tocolytic agent for the future," as it was found to inhibit both spontaneous and oxytocin-induced contractions via stimulation of a calcium receptor that causes relaxation in smooth muscle cells.11

Cholesterol likewise is increased in obesity and has been shown to inhibit the contractile activity of myometrial cells. Multiple other neurochemical factors and adipokines, such as ghrelin and even the oxytocin receptor itself, have been implicated in studies regarding obesity-related labor dystocia.10

Evidence-Based Labor Management of the Patient With Obesity

First Stage of Labor

Obesity was identified as an independent risk factor for intrapartum cesarean by Nuthalapaty et al12 in 2004. As the rising cesarean rate subsequently became a topic of international conversation, the disproportionate ratio of obese women at risk of intrapartum cesareans due to first- [odds ratio (OR), 3.54] and second-stage (OR, 2.18) arrest was brought to light.7 This prompted the question, are we intervening too soon?

Zhang et al7 redrew the partogram with labor data obtained from a "contemporary" cohort-contemporary referring to a population with an increasing maternal age and BMI who no longer was well represented by the Friedman labor curve, which was extrapolated from a small, homogeneous population in the 1950s.7 From this curve, both the modern definition of active phase labor, beginning at 6 cm, and the guidelines for diagnosis of arrest of dilation (>4 hours with adequate and >6 hours with inadequate contractions) were derived.

The contemporary curve was specifically redrawn by parity and BMI category in 2011 by Kominiarek et al6 (Figures 1 and 2). From this analysis, we learned that, regardless of parity, as a patient's BMI increases, so does the amount of time required per centimeter of cervical change, and total labor duration. According to their model, if labor courses are compared head-to-head, a nulliparous patient with a normal BMI may reach 10 cm a full 1.2 hours earlier than a patient with a BMI more than 40. This trend persisted despite whether labor was spontaneous, augmented, or induced.

Figure 1. Labor curves in multiparas by BMI Category. (Adapted from

Figure 2. Labor curves in nulliparas by BMI category. (Adapted from

Norman et al8 recreated the labor curves of 5200 women with term, singleton pregnancies in a population with a greater than 50% prevalence of obesity-all of whom completed the first stage of labor. They found, for both nulliparous and multiparous women, the effect of obesity was most evident in the latent phase, which was significantly longer and did not accelerate until an inflection point of 6 cm. They noted that a pronounced delay in rate of change occurred in patients with obesity between 4 and 6 cm. This difference ultimately led to an impressive median 2 additional hours required to complete the first stage when compared with nonobese counterparts.8 Another study by Vahratian et al9 closely examined the subtle differences in labor progress and duration in women with obesity. They again found that these women took significantly longer to reach 10 cm than women of normal weight, with this delay concentrated around 4 to 6 cm in the overweight group versus 7 cm in obese women. These studies together have significant implications for the diagnosis of first-stage arrest and performance of premature intrapartum cesarean in patients with obesity.

Intrapartum Monitoring

Multiple difficulties with external fetal monitoring arise in the setting of obesity. Despite our best efforts, fetuses of women with obesity spend comparatively more time unmonitored throughout the labor course. Increased interposed adiposity between the uterus and monitors results in frequent necessary adjustments, and restriction of intrapartum movement for the patient. Open communication, along with shared decision-making with the patient and nursing staff regarding continuous monitoring, may help quell frustrations and improve satisfaction.

Reliable fetal and uterine contraction monitoring are essential components of intrapartum management. Patients with obesity are at higher risk for dysfunctional labor and often have higher oxytocin requirements, but the ability to successfully monitor the fetal heart rate and uterine contractions is often the rate-limiting factors. We also know intrapartum cesarean performed for fetal distress is more common with increasing BMI, which only adds to the necessity.4 Ultimately, women with obesity, especially class III obesity, are much more likely to require premature artificial rupture of membranes, internal fetal monitoring, and intrauterine pressure catheter placement to respond to these challenges.16

Alternative monitoring methods are on the horizon. New equipment using abdominal surface electrodes has already been studied in the obese population. Abdominal fetal electrocardiogram (afECG) and electrohysterogram (EHG) data are obtained from the same electrode array placed externally on the maternal abdomen. Cohen et al16 asserted that afECG and EHG should be "the preferred technique" for intrapartum monitoring in women with high body mass given that afECG and EHG data were unaffected by maternal obesity, whereas fetal heart rate data obtained from Doppler ultrasound were shown to degrade directly with increasing maternal BMI.

Equipment and Resources

Standard hospital equipment is often not optimal for patients with obesity. Maternal monitor belts, gowns, compression stockings, labor rooms, beds, toilets, and operating tables should be outfitted appropriate to body size. It is imperative to familiarize ourselves with weight limits of examination and operating tables. In addition, undersized adult blood pressure cuffs may falsely elevate the blood pressure reading and cause significant discomfort if applied to obese patients. Given increased risks of autonomic instability, preeclampsia, and hemorrhage, accurate blood pressure monitoring is essential. If accurate blood pressure readings cannot be obtained via cuff, placement of an arterial line may be considered.14 With regard to operative equipment, specialized transfer devices such as the Hover mat, long instruments, and additional assistants, tape or devices, to aid in retraction may significantly impact the safety and efficiency of each procedure.

Anesthesia Considerations

Just as obesity confers increased obstetric risk, it also increases risks associated with peripartum anesthesia. Patients with obesity are specifically known to have increased risk of failed initial epidural placement (up to 42% in class III obesity), multiple attempts at placement, epidural migration within subcutaneous tissue, and ultimately higher rates of general anesthesia and intubation (up to 33% in class III obesity).17 Epidural placement is notoriously challenging in the obese population and requires more time to correctly position the patient, identify appropriate landmarks, and to allow for replacement in the event of failure. Given these challenges, many articles in the literature suggest early placement of epidural catheters after discussion of risks and benefits.17 ACOG also notes that early regional anesthesia may reduce "decision-to-incision" time, given the known increased risk of emergent cesarean in obese parturients.18 Combined spinal-epidural may also be preferred to spinal in the event of impending cesarean, given the ability to extend the length of medication efficacy in the event of longer operative times.

Some complications of regional anesthesia, including dural puncture, are more frequently seen in the obese population. In a study of 575 women undergoing scheduled cesarean under spinal anesthesia, escalating BMI was found to be associated with increased total spinal time, needle length, and number of attempts-but serious complications such as high spinal and conversion to general remained low.19 Despite the overall low incidence of serious complications, in a recent 2007 review of anesthesia-related maternal mortality in Michigan, a staggering 75% of the patients who died were obese.20

Given disproportionate risk and frequency of comorbidities in pregnant patients with obesity, antepartum anesthesia consultation in the third trimester, or at the very least on admission to the labor floor, is strongly recommended in the anesthesia literature and by ACOG.17,18 Early consultation and clear communication between obstetric and anesthesiology providers are critical for adequate planning, airway evaluation, and avoidance of rare, but potentially catastrophic, anesthesia complications.

Second Stage of Labor

Historically, the dysfunctional labor seen in obesity was thought to be mainly secondary to fetal macrosomia and resultant cephalopelvic disproportion, poor maternal cardiovascular fitness, and maternal "soft tissue dystocia," all of which primarily affect the second stage of labor. Interestingly, when Zhang's contemporary labor curve was examined for effects of obesity on the second stage, durations were found to be similar throughout BMI groups in nulliparas, and, somewhat counterintuitively, were decreased in multiparas with obesity.6 Similarly, intrauterine pressure catheter data have shown no difference between the pressures generated by women with obesity versus women of normal weight.21 Norman et al8 identified that once the second stage was initiated, obese and nonobese patients had similar risk of cesarean delivery.

Obesity increases the risk of operative vaginal delivery. Specifically, women with BMIs more than 30 and more than 40 are respectively 1.5 and 2 times as likely to be delivered via vacuum or forceps.5 Given increased risks of both fetal macrosomia and shoulder dystocia in patients with obesity, combined with the known fetal and maternal risks of operative delivery, women with obesity should be selected judiciously and counseled appropriately before operative delivery.

Induction of Labor

Obesity alone is not currently an indication for induction of labor per ACOG; however, women with obesity are more likely to be induced than the general population.18 This is another association, which seems to vary incrementally with increased weight. In one large population cohort study, 28% of women of a normal BMI were shown to require induction of labor, whereas women with obesity were increasingly likely to be induced per BMI class (30.4% of women in class I, 32.5% in class II, and 34.0% in class III, respectively).22 Obesity increases the likelihood of induction for comorbid medical indications such as diabetes and hypertensive disorders, and for prolonged pregnancy.12,23

As previously discussed, multiple biochemical factors contribute to delayed onset of labor in patients with obesity. With increased levels of multiple factors known to inhibit ripening, spontaneous membrane rupture, and uterine contractions, it is unsurprising that obese women are more likely to be induced for post-term pregnancy. In a retrospective study of over 9000 patients giving birth at a tertiary care center, obese women were found to have a nearly 70% higher adjusted odds of reaching 42 weeks' gestation compared with women of normal BMI.24

All previously published retrospective data have indicated that inductions of parturients with obesity are more likely to fail than those of their normal-weight counterparts. In the cohort study by Wolfe et al,22 obese women were 2 to 3 times as likely (class I, 20.2%; class II, 24.2%; and class III 29%) as normal-weight counterparts (13%) to have a failed induction. The likelihood of failure was most pronounced in nulliparas with macrosomic infants. Recently, the dogmatic teaching that induction of labor confers an inherently elevated cesarean risk has been refuted in several studies comparing induction of labor with expectant management. One retrospective cohort study specifically analyzed induction at 39 weeks versus expectant management in a nulliparous obese population and demonstrated that elective induction at 39 weeks resulted in fewer cesarean deliveries [35.9% vs 41.0% respectively (P < 0.05); adjusted OR, 0.82; 95% confidence interval (CI), 0.77-0.88], and reduced maternal and neonatal morbidity.23

In a prospective study of 509 nulliparous patients undergoing labor induction via a standardized protocol, the rate of cervical dilation was shown to be slower, inductions longer, and intrapartum cesarean more likely with increasing maternal weight.12 Pevzner et al25 examined the effect of obesity on induced labor noting that women of normal weight delivered on average 2 hours sooner than women with BMIs from 25 to 30 and 4 hours before women with BMIs more than 40.

Along with increased duration of induction, obesity has been associated with increased requirements of both ripening agents and oxytocin to achieve vaginal delivery.25,26 Several biologic mechanisms may explain this trend, including increased volume of distribution, competitive inhibition from biochemical factors, and altered pharmacokinetics of ripening agents and oxytocin in the face of increased adiposity. Ellis et al27 found that women with obesity required both increased number of doses, and higher overall amounts of prostaglandins for ripening as compared with women of normal weight.

With regard to the selection of a particular ripening agent in the patient with obesity, one retrospective study demonstrated that misoprostol had better ripening outcomes, lower cesarean rates, and no increase in morbidity as compared with dinoprostone.28 Given these findings, and the relatively lower cost of misoprostol, it is reasonable to favor misoprostol for induction of labor in the obese patient.

Pevzner et al. performed a secondary analysis of a large, randomized controlled trial and found that patients with obesity required a greater median dose and longer duration of oxytocin than normal-weight counterparts to achieve a vaginal delivery.25 Similarly, a retrospective study by Roloff et al26 suggested that increasing total amounts of oxytocin was required with increasing BMI class. Yet, low-dose oxytocin protocols are often universally applied despite known increased requirements per BMI category. Of note, ACOG supports the use of both low-dose (2 mU/h, increased by 2 mU/h) and high-dose (initial dosing of 6 mU/h, increased by 6 mU/h) oxytocin protocols.29

Cesarean Delivery

Although the overall cesarean rate in the United States is estimated at 32% of deliveries, this percentage skyrockets when the obese population is examined separately. One large, multicenter study demonstrated that the absolute risk of cesarean delivery in nulliparous women with BMIs 35 or more reached nearly 50%.5 Similarly, Cedergren4 determined that class III obesity quadrupled a woman's risk of cesarean for labor arrest.

The altered physiology of labor, challenges with fetal monitoring, and medical comorbidities associated with obesity all contribute to the increased cesarean rate of this population. However, multiple studies have shown that after controlling for confounding medical or obstetric covariates like hypertensive disorders, diabetes, macrosomia, and fetal growth restriction, the cesarean rate for this population is still intrinsically higher.12,30,31

In fact, the risk of cesarean in laboring patients has been shown to increase linearly and incrementally with BMI as a continuous variable, estimated by Kominiarek et al31 as 2% to 5% per 1 kg/m2 increase in BMI, depending on parity and whether the woman has a history of cesarean. To put this into perspective, directly correlating with BMI, a woman with a BMI 30 or more is 2 to 3 times more likely than a woman with a BMI less than 25 to have a cesarean, regardless of parity. This risk is approximately doubled in the setting of a trial of labor after cesarean.

Cesarean deliveries in patients with obesity are higher risk procedures, particularly when performed intrapartum.30 So why not perform elective, prelabor cesareans in obese women? A retrospective cohort study of 661 women with class III (BMI >40) obesity by Subramaniam et al32 sought to determine optimal mode of delivery for this population. As expected, women who had successful inductions ending in vaginal delivery had the best outcomes, whereas women who had failed inductions and subsequent cesareans had the worst outcomes. In a subsequent study by Hopkins et al33 comparing induction versus scheduled cesarean, trial of labor remained cost-effective until intrapartum cesarean rate exceeded 70%.

Women with obesity who deliver via cesarean have a higher risk of infection, thromboembolism, and maternal mortality as compared with both women with obesity who deliver vaginally and women of normal weight who deliver via cesarean.30 Although a planned cesarean confers less risk than an intrapartum cesarean, one must also consider the cumulative risk of subsequent repeat cesarean deliveries throughout a patient's reproductive lifetime. In third or higher-order cesarean deliveries, maternal obesity has been specifically associated with a higher composite maternal morbidity (uterine rupture, hysterectomy, blood transfusion, bowel or bladder injury requiring repair, intensive care unit admission, thrombosis, reoperation, or maternal death; OR, 4.36, 95% CI, 1.21-15.75), and low 1-minute Apgar scores.34

Operative Considerations

Cesarean deliveries complicated by obesity present several logistical challenges, including additional personnel, increased time to administer anesthesia, specialized surgical equipment, and longer operative times. These considerations are even more relevant in the middle of the night or if surgical resources are limited in some way. Meticulous operative planning and technique may help prevent complications in patients with obesity.

When considering the orientation and location of skin incision, it is important to take the individual patient and distribution of adiposity into account, and anticipated type of uterine incision. Additionally, abdominal architecture may be distorted, and the umbilicus is not always an appropriate landmark.

Although a vertical skin incision allows for rapid entry compared with transverse incisions, it has been associated with a 12-fold increase in need for postoperative wound exploration, and increased risk of dehiscence, hernia formation, and increased postoperative pain in patients with obesity14 A transverse incision is therefore recommended, especially when a transverse uterine incision is anticipated. Vertical skin incisions have been shown to increase the likelihood of vertical uterine incisions.35

A transverse incision should be made at the abdominal level that balances several goals: obtaining the thinnest subcutaneous layer, ease of access to lower uterine segment, and ideal (cephalad or caudal) pannus retraction to access the desired incision site. Supraumbilical, infraumbilical, and suprapubic incision sites are reasonable options, although supraumbilical incisions have been associated with a greater risk of classical hysterotomy and associated morbidity in women with class III obesity.36 Although suprapannicular versus infrapannicular incision placement has not been shown to influence risk of surgical site infection, generally speaking, the deep skinfold under the pannus should be avoided due to potential difficulties keeping this area clean and dry in the postoperative period.14

The abdominal wall may be retracted with surgical tape, adhesive straps, or commercially available devices such as atraumatic/elastic self-retaining abdominal retractors or adhesive panniculus retractors. Consideration and monitoring of patient comfort, dignity, and respiratory function are of utmost importance, especially given potential chest wall compression with cephalad retraction.14,35

Fascial closure should be performed with an absorbable monofilament suture in 1 x 1-cm bites, with a 4:1 suture: incision length ratio to avoid fascial necrosis and dehiscence.14 Reapproximation of a subcutaneous fat layer by at least 2 cm has been shown to decrease the risk of postoperative wound disruption by up to 34%-a benefit that was not improved when combined with drain placement.37,38 Wound vacuum placement has been evaluated on a prophylactic basis in multiple studies; however, in meta-analysis, this intervention failed to reduce composite wound complication risk.14

Wound closure with staples is often preferred by providers given the known increased risk of postoperative wound exploration in this population.14 However, a large recent meta-analysis by Mackeen et al39 demonstrated that patients with obesity were 49% less likely to have wound complications with sutures as compared with staples (6.69% vs 12.84%; relative risk, 0.51; 95% CI, 0.34-0.75).

Antibiotics

The volume of distribution and clearance of certain antibiotics are both increased in obesity, and preoperative cefazolin dosing was increased from 1 to 2 g based on bariatric surgery literature that showed decreased tissue levels in patients with obesity. Further increase to 3 g of cefazolin (as compared with 2 g) was evaluated in a retrospective cohort study, and this did not decrease surgical site infections in cases complicated by morbid obesity. Patients with obesity are at risk for prolonged operative times, and it is important to recall that more frequent antibiotic redosing may be necessary in this scenario.40

Postoperative antibiotic administration may be considered to mitigate the increased risk of surgical site infection in the obese population. A study by Valent et al demonstrated reduced risk of infection in patients with obesity when, in addition to standard preoperative prophylaxis, a postoperative regimen of oral cephalexin 500 mg and metronidazole 500 mg was given every 8 hours for 48 hours postoperatively. This study did not account for preoperative administration of azithromycin in unscheduled cesareans; therefore, this regimen would be most appropriate for patients who did not receive azithromycin before their cesarean delivery.40

Conclusion

Obesity is an epidemic in the United States, with widespread impact on reproductive-aged women. It is imperative that providers practicing obstetrics increase their knowledge base surrounding the risks that obesity portends to the maternal-fetal dyad, and the biochemical mechanisms that contribute to these challenges. Understanding and anticipating these risks, and embracing an evidence-based approach to management of our pregnant patients with obesity in the intrapartum period will ensure enhanced safety with a goal for optimized outcomes for both patients involved.

Practice Pearls

* Obesity is an increasingly prevalent medical condition with significant implications for the management of labor and delivery. Obstetricians must become both comfortable and familiar with evidence-based methods of counseling and caring for patients with obesity.

* Both providers and health care facilities should be equipped with appropriate expertise, equipment, and resources to care for obstetrical patients with obesity.

* Obesity is associated with labor dystocia in the first stage, with delays concentrated around 4-7 cm. Diagnosis of arrest disorders should take these altered labor curves into account.

* The second stage of labor is largely unaffected by obesity-related biochemical changes; however, operative vaginal delivery is more common.

* Induction of labor is more common, takes longer, and is at higher risk for failure in patients with obesity; however, induction at 39 weeks may reduce composite maternal and fetal risk in nulliparous patients with obesity as compared with expectant management.

* Increased doses of many commonly used medications, including antibiotics, induction agents, and oxytocin, may be required in the obstetric management of patients with obesity.

* Third-trimester consultation with anesthesia is recommended in class III obesity, and placement of early epidural may be considered.

* Meticulous preoperative planning and certain intraoperative techniques may reduce inherently increased odds of postoperative complications in patients with obesity, including:Ensuring availability of staff and equipment;Meticulously planned surgical incisions, retraction, and exposure; andAppropriate fascial, subcutaneous, and skin closure with absorbable, monofilament sutures.

REFERENCES