Labour and Delivery in Women With a High Body Mass Index

Introduction

Obesity has become a new epidemic, affecting all ethnic and racial groups. In the developed world, its incidence is persistently increasing, resulting in higher rates of overweight and obesity than normal body mass index (BMI) in some countries. In developing countries, obesity exists alongside malnourishment. More than 20 years ago, the World Health Organization (WHO) formally recognized obesity as a global epidemic. Despite increasing efforts to address this public health issue, the prevalence of obesity continues to rise dramatically. With rising rates of obesity in women of reproductive age, obesity complicates a significant proportion of pregnancies. In the USA in 2014, half of all pregnant women were either overweight (BMI ≥ 25, 25.6%) or obese ( BMI ≥30, 24.8%).

Pregnancies in women with obesity are at increased risk for adverse maternal and neonatal outcomes. For the fetus and neonate, risk of preterm birth, large-for-gestational-age live birth, macrosomia, shoulder dystocia, congenital anomalies, birth injury, stillbirth, cerebral palsy, and neonatal and infant death are increased. For the mother, risk of hypertensive disorders of pregnancy, gestational diabetes, induction of labour, caesarean delivery, anaesthetic and surgical complications, endometritis, thromboembolic diseases and postpartum haemorrhage are increased.

In this chapter we will discuss the intrapartum management of patients with obesity, primarily focusing on the operative and anaesthetic techniques unique to this population.

Definition

Obesity is defined by the WHO as excessive fat adipose accumulation. The amount of body adipose can be assessed by many different anthropometric measures, of which BMI in the most commonly used measure. BMI is calculated as an individual’s weight in kilograms divided by the height in metres squared. Commonly used definitions of weight based on BMI were established by the WHO and are presented in Table 33.1 . BMI has been widely incorporated into clinical practice, as it is a simple, noninvasive method. Additionally, many previous studies have shown associations between BMI-defined obesity and mortality. Lastly, and particularly so in individuals with high BMI, it correlates with accurate measurements of percent body adipose, such as densitometry. However, defining obesity based on BMI has disadvantages as well. This tool does not differentiate between lean body mass and fat body mass, i.e. adiposity. Moreover, BMI does not provide any information on the distribution of body adipose. This is of high importance since abdominal obesity has been shown to be associated with significantly higher health risks as well as pregnancy-associated complications.

TABLE 33.1

World Health Organization Body Mass Index Classifications

BMI kg/m ²	Classification
<18.5	Underweight
18.5–24.99	Normal weight
25.00–29.99	Overweight
≥30.00	Obese
30.00–34.99	Obese class I
35.00–39.99	Obese class II
≥40.00	Obese class III

Anthropometric measures other than BMI are not realistic during pregnancy as they rely on skinfolds in different locations and may be difficult to obtain due to increasing skin tension in pregnancy. Moreover, many of these alternative measures have not been validated in the pregnant population.

Consequently, currently obesity is most often defined by BMI, despite its limitations. Nonetheless, one should keep in mind that it can provide misleading information regarding the actual body fat content, particularly when measured in pregnancy.

Incidence

Caesarean delivery (CD) rates in the western world have been rising persistently, mirroring the increase in obesity trends. In fact, the prevalence of CD increases linearly with rising BMI. Nearly half of all women with BMI ≥50 undergo CD, compared with one-third of women with class I or II obesity (BMI 30–39.9) and 43% of women with class III obesity (BMI 40–49.9).

Compared with women of normal BMI, nulliparous women with overweight and singleton pregnancies have a 1.5-times higher risk of CD, whereas those with class I and II obesity (BMI between 30.0 and 39.9) have a 2.25-times higher risk.

CD presents operative challenges unique to this population. Preoperative planning has a direct effect on intraoperative and postoperative outcomes and can mitigate complication rates that may otherwise be unnecessarily high in these patients.

History and Examination

Preoperative Patient Assessment

Cardiovascular assessment – Cardiovascular disease of many types is more common in patients with extreme obesity. Obesity alone and comorbid disease such as chronic hypertension can lead to cardiac dysfunction in pregnancy due to an increase in cardiac output and preload. Therefore, if the history and/or physical examination provide any suspicion for cardiovascular disease, especially when assessment of exercise tolerance is uncertain, there should be a low threshold for a formal cardiology consult, including electrocardiogram and echocardiogram.
Respiratory assessment – Obstructive sleep apnoea (OSA), defined as recurrent episodes of upper airway collapse during sleep, increases the risk of CD and also increases the risk of postoperative complications. Importantly, women with OSA are at increased risk of hypercapnia and hypoxaemia during CD. Though presently there are no studies showing a benefit to treatment of OSA in improving surgical outcomes, given the high frequency of this condition in individuals with obesity, preoperative screening is reasonable.
Skin assessment – As intertriginous infections below the pannus are common, a skin examination is helpful to assess potential for areas of wound breakdown should caesarean birth be necessary.

Obstetrical Management

Preoperative Antibiotics

Obesity is a significant risk factor for surgical site infections (SSI), with three- to five-fold increased rates for postcaesarean SSI. Although in the normal weight population the incidence of postcaesarean wound complications ranges from 3% to 17%, in women with BMI ≥50 it is as high as 30%. Women with obesity who undergo a CD due to an unsuccessful labour attempt are at an even higher risk.

Medical comorbidities (i.e. diabetes mellitus, chronic hypertension and preoperative skin breakdown) along with longer operative times and higher blood loss all contribute to this greater incidence. This high risk is increased further by lower tissue concentrations of prophylactic antibiotics in patients with obesity.

Due to the lack of studies focusing on the pharmacokinetics of antibiotics among women with obesity BMI ≥50, there is substantial controversy regarding the optimal dosing of perioperative antibiotics. Based on pharmacokinetic data primarily from nonpregnant patients with obesity, for women with a BMI of 30 or greater or weighing more than 100 kg, a single 2-g dose of cefazolin prior to skin incision is recommended. In two randomized controlled trials (RCTs) of 3 g versus 2 g cefazolin, there was no difference in the percentage of women above minimum inhibitory concentration (MIC) for both gram-positive and gram-negative bacteria at either dose. However, higher adipose tissue concentrations of cefazolin were observed with the higher dose in patients with higher BMI. Despite this finding, other studies did not show that higher doses in obese women reduced rates of SSI. A recent study showed benefit to the addition of azithromycin to cefazolin in SSI prevention in women undergoing a CD in labour. Patients with obesity undergoing a CD in labour are no exception, and should receive this regimen as well.

Patient Positioning

There is theoretic concern over hypotension after administration of spinal anaesthesia and resultant fetal bradycardia. Nonetheless, a recent Cochrane review of RCTs of all women undergoing CD did not demonstrate any maternal or fetal benefit from maternal positioning. The studies included in this review, however, did not focus on women with obesity. Still, special attention should be given to maternal positioning and pressure point reduction during a CD. Since operative duration in women with obesity is longer than that for women with normal weight, padding pressure points is important to prevent skeletal muscle necrosis. Postoperatively, caregivers should have a heightened awareness that neuromuscular complaints in patients with BMI ≥50 can be a sign of rhabdomyolysis, which can lead to acute renal failure.

Panniculus Retraction and Retractors

Although most women with BMI ≥50 will require retraction of pannicular tissue at the time of CD, there is scarce literature on the benefits and risks of this practice. Options for panniculus retraction include surgical tape, Montgomery traps, adhesive straps applied to the maternal abdomen and tied to the bed railing to retract the panniculus cephalad, or the use of plastic sterile adhesive sheets.

In women with BMI ≥50 undergoing CD, self-retaining retractors are frequently used for operative visibility. In our practice, we use elastic self-retaining retractors, such as Alexis O (Applied Medical, Rancho Santa Margarita, CA) or Mobius (Cooper Surgical, Trumbull, CT) retractors, which have been associated with less postoperative analgesia and shorter operative time compared with conventional metal retractors.

Operative Management

You're Reading a Preview

Become a Clinical Tree membership for Full access and enjoy Unlimited articles

Become membership

If you are a member. Log in here