One of the downstream consequences of the epidemic of obesity in the USA is that more women are entering pregnancy already suffering from the burden of overweight and obesity. There are a myriad of adverse outcomes associated with a pregnancy complicated by obesity, including subfertility, preeclampsia, fetal macrosomia, and cesarean delivery. Obstetrical complications can increase as much as threefold in obese versus nonobese mothers. Obesity is a common risk factor for insulin resistance. Insulin sensitivity is already reduced by 50–60 % over the course of pregnancy, so it is not surprising that overweight or obese women who are prone to beta-cell dysfunction and glucose intolerance prior to pregnancy are at increased risk of gestational diabetes (GDM) during pregnancy (Fig. 1.1) [3, 4]. For example, in comparison to women with a normal body mass index, the risk of developing GDM rises exponentially with increasing BMI, with odds ratios (OR) of 1.97 (95 % CI 1.77–2.19), 3.01 (95 % CI 2.34–3.87), and 5.55 (95 % CI 4.27–7.21) for those who are overweight obese and morbidly obese, respectively [5]. Other markers of obesity, such as waist circumference and waist-to-hip ratio, are independently associated with a higher 2-h post-glucose response, suggesting that central obesity is an independent predictor of GDM.

Overweight and obese women are at increased risk for excessive gestational weight gain (GWG) [4–6]. The combination of pre-pregnancy overweight and obesity and excessive GWG is particularly concerning. The most recent Institute of Medicine (IOM) recommendations [7] for a smaller weight gain range for those classified as overweight (7–11.5 kg) and obese (5–9 kg) have garnered considerable attention. Longitudinal studies show a direct association between maternal obesity and infant birth weight. For women who are overweight or obese prior to conception, an increase in GWG is associated with an increase in fetal adiposity. The combination of maternal overweight or obesity and exceeding the IOM guidelines increases the risk of delivering a large-for-gestational-age infant and the associated complications of dysfunctional labor and potential cesarean delivery [8].

A growing concern, from both a clinical and public health perspective, is the intrauterine environment and the concept of transgenerational obesity (Fig. 1.1) [9, 10]. Obesity, GDM, and excessive weight are thought to change the intrauterine environment and contribute to increase risk of obesity in children. Early work by David Barker [1, 11] set the stage for ongoing research in fetal programming and development of adult diabetes and hypertension [12]. The Barker hypothesis postulates that nutritional insults to the fetus during critical periods of development may lead to in utero alterations in fetal metabolism or fetal programming that favors obesity-related conditions in adulthood. Of particular interest is the hypothesis that offspring of women with obesity may be predisposed to greater energy consumption and higher levels of sedentary behavior, a finding that is supported by animal models. Though outside the scope of this text, animal models have been useful in elucidating the contribution of maternal phenotypes (e.g., obesity and dietary intake) on the intrauterine environment and growth trajectories in the offspring [13]. The combination of obesity and pregnancy, inflammatory markers, adipokines, and the hormonal milieu contributes to a complex interrelation of mechanisms that with further research can broaden our understanding of the transgenerational effects of obesity.

Breaking the cycle of transgenerational obesity will require a better understanding of the epidemiological and clinical aspects of obesity as well as the translation of science into standardized clinical care and targeted interventions across the life span of women and children. To date, there are few published texts that translate the evolving state of the science of overweight and obesity from the maternal and child health perspective. The overall objectives in writing this book are to (1) translate the state of the science on overweight and obesity in the perinatal period, thus arming clinicians and public health officials that provide care to childbearing women with the knowledge necessary to communicate with their patients on the effects of obesity in this important time period; (2) communicate important clinical aspects of care that can be effectively communicated to patients by their providers in a busy practice setting; and (3) summarize the evidence for perinatal, family, and community lifestyle interventions that have been shown to be effective in promoting a healthy weight and modifying the risk of developing diabetes and obesity.

This book is our attempt to summarize the latest developments in our clinical understanding of obesity in pregnancy. Obesity is a multicomplex disease, and prevention and treatment will require transdisciplinary approaches, including clinical, research, and population-based perspectives. The content of the book differs from other textbooks on obesity because each chapter is written from a clinical and population-based perspective. Our collaborative team of experts provides important, relevant insight into each topic, emphasizing the intersection between clinical care, research, and broad dissemination of research findings. The first section provides an overview of the biological mechanisms underlying the clinical effects of obesity on the expectant mother and developing fetus. Dr. Calhoun reviews the biological pathways that account for the effect of obesity on infertility and subfertility. She summarizes the current clinical care of the overweight or obese woman and subfertility, and the lifestyle and medical options currently used to achieve conception. Both the preconception period and pregnancy represent important teachable moments in the lives of childbearing age women. Of particular concern to clinicians and public health officials is the contribution of pre-pregnancy obesity to the persistently high rates of medical complications of pregnancy (diabetes, hypertension) and adverse birth outcomes (preterm birth, low birth weight infants, and infant deaths) [14]. Dr. Witkop outlines important steps in preconception and pregnancy care in the overweight or obese women and the clinical issues to consider during this critical time period. Her chapter provides a step-by-step assessment for preconception care that can be used by multiple types of providers in diverse clinical settings. She summarizes the Institute of Medicine gestational weight gain guidelines and the role of clinicians in promoting a healthy weight before and during pregnancy. Also in this section, Dr. Witkop discusses the complex decisions faced by women and their clinicians and the important role of shared decision making in developing a labor and delivery plan that incorporates best practice and patient preferences.