Episode Details

Episode 156: Obesity, Fertility, and Pregnancy

Future Dr. Hamilton defines obesity and explains the pathophysiology of obesity and its effects on fertility and pregnancy. Dr. Arreaza adds some input about the impact of epigenetics on newborn babies.  

Written by Shelby Hamilton, MS3, American University of the Caribbean School of Medicine. Editing by Hector Arreaza, MD.

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Definition of obesity

Obesity is a multifactorial chronic disease that is increasing in prevalence across the globe. It can be defined as a body mass index (or BMI) greater than 30 kg/m2. According to the CDC from 2017-March 2020, the prevalence of obesity in United States adults was 41.9%.

Classification of obesity by BMI.

Obesity can further be divided into three classes: class I which is a BMI between 30-34.9; class II which is a BMI between 35-39.5; and class III which is a BMI greater than 40. We recommend avoiding the term “morbid obesity” because of the negative connotation of the word “morbid.” Class III or severe are better terms in those cases. 

This classification is based on the individual risk of cardiovascular disease. One of the greatest health consequences affecting individuals with obesity is the cardiovascular effects including hypertension, dyslipidemia, and coronary artery disease. Other effects include insulin resistance and diabetes, cholelithiasis, non-alcoholic fatty liver disease, osteoarthritis, and even depression.

How Does Obesity Affect Fertility?

Obesity can have an extensive effect on the overall health of an individual. In addition to these commonly discussed effects, obesity can also influence a person’s fertility. This is especially observed in women with polycystic Ovary Syndrome (PCOS) who have a greater BMI and also have symptoms of anovulation. Excess adipose tissue plays a role in the effects that obesity has on fertility. 

White adipose tissue can secrete a specific group of cytokines known as ‘adipokines’. These adipokines include leptin, ghrelin, resistin, visfatin, chemerin, omentin, and adiponectin. With a greater percentage of adipose tissue, there are higher rates of hypothalamic gonadotropin hormonal dysregulation, which can be combined with insulin-related disorders, low sex hormone binding proteins, and high levels of androgens. The combination of these factors can result in decreased ovarian follicle development and decreased progesterone levels.

Hormonal changes

Obesity is an endocrine disorder. One specific adipokine that affects the hypothalamic-gonadotropin axis is chemerin. Chemerin impairs the release of follicle-stimulating hormone (FSH) from the pituitary gland. This reduction in FSH release consequently leads to anovulation, meaning that no egg will be released from an ovarian follicle, contributing to infertility. 

Shelby: Another adipokine affecting fertility is adiponectin. The receptors of adiponectin are predominantly expressed in reproductive tissues, including the ovaries and endometrium. In individuals with a greater BMI, a decrease in adiponectin secretion has been observed, resulting in decreased stimulation of its receptors, especially in the endometrium, which has been linked to recurrent implantation failure. Adiponectin has also been shown to affect glucose uptake in the liver. With reduced adiponectin levels, there is reduced hepatic glucose uptake, leading to i