Pregnancy and Obesity

Cynthia Maxwell, Dan Farine, Cynthia Maxwell, Dan Farine

• Publisher: De Gruyter
• Year: 2017
• Print ISBN: 9783110486247
• eBook ISBN: 9783110486353
• Edition: 1
• Topic: Medicine
• Subtopic: Gynecology, Obstetrics & Midwifery

Obesity epidemic is a global problem of the 21th century for women in reproductive age and also the obstetricians and pediatricians. There are influences of mother's prepragnancy and antepartal obesity, at delivery, for fetal programming and for maternal and fetal lifelong metabolism. The epidemiological results are important, but for the health care providers the skills for prevention of mother's obesity with all consequences are essential. Evaluated programms in nutrition and physical activity will be discussed.

Section I: Planning for pregnancy

Miha Lučovnik, Nataša Tul and Isaac Blickstein

1Epidemiology of obesity

1.1Introduction

Obesity is a medical condition in which an excessive amount of adipose tissue has accumulated to the extent that it may impair health [1]. Excess body fat is deleterious to multiple organ systems through thrombogenic, atherogenic, oncogenic, hemo dynamic, and neurohumoral mechanisms [2,3]. Numerous epidemiological studies have demonstrated associations between obesity and various diseases, such as diabetes mellitus, heart disease, and several types of cancer [2–7]. Obesity has also been shown to have a negative effect on psychosocial as well as economic aspects of life [8].

In 1997, the World Health Organization (WHO) formally recognized obesity as a global epidemic [1]. Despite multiple efforts to address this public health issue, the prevalence of obesity continues to increase [1]. As the prevalence of obesity is increasing, so is the number of obese women of reproductive age. Consequently, obesity complicates a significant proportion of pregnancies [9]. These pregnancies are at increased risk of several maternal as well as fetal adverse outcomes, which are described in more detail elsewhere in this book.

In this chapter, we will discuss different methods to diagnose excess adipose tissue (obesity). We will also review current epidemiological data on the prevalence of obesity in the general population as well as specific data on the prevalence of obesity in pregnant women.

1.2Definitions of obesity – advantages and disadvantages of using body mass index

Obesity is defined by the WHO as excessive fat accumulation [1]. However, the amount of body fat can be assessed by many different measures. The body mass index (BMI) is the most commonly used anthropometric method to define obesity. BMI is calculated as an individual’s weight in kilograms divided by the height in meters squared. This measurement was first described by a Belgian mathematician Adolphus Quetelet in the mid-19th century based on the observation that body weight was proportional to the square of the height in adults with “normal body frames” [10]. Commonly used definitions of underweight, normal weight, overweight, and obesity based on BMI were established by the WHO and are presented in Tab. 1.1 [11]. As Asian populations develop negative health consequences of obesity at a lower BMI, some nations redefined different BMI cutoffs for obesity. The Japanese defined obesity as any BMI greater than 25, whereas China uses a BMI of greater than 28 [12, 13].

Tab. 1.1: Classification of adult underweight, overweight, and obesity according to BMI [11].

Category	BMI
Underweight	<18.5
Normal weight	18.5–24.9
Overweight	25.0–29.9
Class I obesity	30.0–34.9
Class II obesity	35.0–39.9
Class III obesity	≥40.0

There are several advantages of using BMI as a diagnostic method for obesity. It is easily applicable in epidemiological studies because it only depends on two commonly measured quantities, i.e., height and weight. BMI has also been widely incorporated into clinical practice due to its noninvasiveness and simplicity. Moreover, numerous studies have shown associations between BMI-defined obesity and mortality [14–16]. BMI also correlates reasonably well with more accurate measurements of percent body fat including densitometry and dual energy X-ray absorptiometry, which are the reference methods for assessment of body composition [17–19]. This is especially true in individuals with high BMIs, indicating that BMI has good specificity and positive predictive value to diagnose obesity.

On the other hand, measuring BMI also presents some disadvantages with regard to pregnancy. The overwhelming majority of studies published on this subject used a BMI cutoff of ≥30 kg/m2 to estimate risks of adverse perinatal outcomes associated with obesity. The main limitation of BMI is that it does not distinguish between the mass associated with bones, muscles and organs (lean body mass), and that associated with fat tissue (body fat mass). BMI, therefore, contains two factors (lean body mass and adipose tissue) that have opposite biological effects. Although adipose tissue has been associated with deleterious health outcomes, preserved lean mass is positively associated with physical fitness, higher caloric expenditure, exercise capacity, and survival [20–22]. Therefore, whereas the specificity of BMI to diagnose excess body fat is high, the sensitivity is relatively low, and as many as 50% of individuals with high body fat percentage are missed by using BMI alone [19]. This issue is even more important in pregnant women because fetal, placental, and amniotic fluid mass represent more or less an unknown part of the total body mass. Moreover, BMI provides no information on the distribution of body fat. This is an important weakness of the method because abdominal obesity has been shown to be associated with significantly greater health risks [23].

Several alternatives to BMI for determining body composition and percentage of body fat have been described and are currently being studied. They are, however, expensive, cumbersome, and/or not insufficiently accurate. Precise determination of body fat content in pregnancy is particularly challenging for several reasons. Some techniques, such as dual energy X-ray absorptiometry or computed tomography, are only rarely applied during pregnancy because of radiation exposure [24]. Methods such as magnetic resonance imaging or underwater weighing use sophisticated equipment that is not available for routine use [25]. Anthropometric measures, other than BMI, for body composition assessment rely on measurements of skinfolds in different locations (e.g., triceps, subscapular, abdominal, and mid-calf) and measurements of different circumferences (e.g., waist, arm, and thigh). Measurements are used in equations that more or less accurately estimate the body fat content [26]. Physiological changes in pregnancy affect skin tension and make measurement of skinfolds challenging, especially in the abdominal region. Consequently, only few anthropometric measurements can realistically be performed during pregnancy. Moreover, the existing anthropometric methods have often been developed for use in nonpregnant women and only rarely specifically for pregnancy [26–28]. Even pregnancy-specific anthropometric methods, however, showed large discrepancies in body composition [29]. Current knowledge, therefore, does not allow selecting a more appropriate method than BMI for reliable routine determination of body fat percentage before and during pregnancy.

In conclusion, obesity is currently most often defined by BMI. This is certainly a useful measure for basic epidemiological evaluation of obesity prevalence. However, BMI can provide misleading information on the actual content of body fat. This is especially true when BMI is measured during pregnancy.

1.3Prevalence of obesity

Obesity has become the most prevalent preventable cause of death worldwide [5]. According to WHO data, the global prevalence of obesity in 2014 was 15% in women and 11% in men. This means that more than 600 million adults were obese in 2014 [1]. Figure 1.1 displays the WHO data on the prevalence of obesity for each country.

Fig. 1.1: World map displaying national data on prevalence of obesity [Source: World Health Organization; available at: http://apps.who.int/bmi/index.jsp].

Fig. 1.2: Obesity trends among US adults. 1990, 2000, and 2010 (Source: Behavioral Risk Factor Surveillance System, CDC; available at: https://www.cdc.gov/obesity/downloads/data/obesity-trends-map_1985-2010.pdf).

Obesity trends are even more worrying than its current high prevalence. The prevalence of obesity more than doubled between 1980 and 2014 and continues to increase worldwide [1]. Figure 1.2 shows the increase in obesity rates among US adults during the period 1990 to 2000. What was once considered a problem of high-income countries is now on the rise in low- and middle-income countries as well [1]. Of special concern is the increase in obesity among children and adolescents. Childhood obesity is associated with a higher risk of obesity, premature death, and disability in adulthood [30]. Moreover, in addition to the increased future risks, obese children experience breathing difficulties, increased risk of fractures, hypertension, early markers of cardiovascular disease, insulin resistance, and psychological effects [31].

Figures 1.3 and 1.4 present data from the SLOFIT system, a national monitoring system of children’s motor and physical development in Slovenia (Slovenia is a European Union member state in Central Europe, with a population of approximately 2 million and 20,000 deliveries per year). The SLOFIT test battery includes eight motor tests (arm-plate tapping, standing long jump, polygon backwards, sit-ups, standing reach touch, bent arm hang, 60 m run, and 600 m run), as well as measurements of the child’s height and weight. Every year, qualified physical education teachers perform the measurements in all primary and secondary schools (high schools) as required by the physical education curriculum, following the official measurement protocol. For the last decade, the proportion of obese high school girls has been increasing (Fig. 1.3). Interestingly, we also found a high proportion (44%–56%) of 18- to 19-year-old girls with normal BMI (18.5–24.9 kg/m2) but reduced exercise capacity (defined as low physical fitness index derived from the eight motor tests used in the SLOFIT system) (Fig. 1.4). These are physically unfit girls, who are most probably maintaining their normal BMI with unhealthy dietary habits and without regular physical activity. Their unhealthy lifestyle makes them at risk of health complications later in life and also during pregnancies. This emphasizes the above-mentioned shortcomings of the BMI to accurately assess body composition and risks for future health.

Fig. 1.3: Increase in prevalence of obesity (defined as BMI ≥30 kg/m2 ) among high school girls in Slovenia (unpublished data, courtesy of Gregor Starc, PhD, Faculty of Sport, University of Ljubljana, Slovenia).

Given the increasing number of obese girls and short-term as well as long-term adverse health consequences of obesity, strategies to prevent obesity by healthier choices of food and regular physical activity should become a high priority in our societies. The first and the ideal goal in managing obesity-associated pregnancy complications is prevention. Clinicians should encourage changes in dietary and physical activity patterns that will lead to weight loss in obese children and adolescents. Realistically, however, the achievement of this goal is very difficult. The lifestyle that leads to obesity is often perpetuated by lack of supportive policies in many sectors: agriculture, food processing, transport, marketing, urban planning, education, and a...

Table of contents

• Cover
• Title Page
• Copyright
• Dedication
• Introduction
• Contents
• Contributing authors
• Section I: Planning for pregnancy
• Section II: Pregnancy management
• Section III: Intrapartum management
• Index