Obesity has become pandemic owing to an obesogenic environment (inexpensive calorie dense food, technologies and structure of communities that reduce or replace physical activity, and inexpensive nonphysical entertainment) and excessive emphasis on low fat intake resulting in excessive intake of simple carbohydrates and sugar. Effects are greater for women owing to their smaller size and extra weight gain with each pregnancy, with 38% of American adult women being obese. Women are responsible for more than three-fourths of the more than 400 billion dollars of excess direct health care expenditures due to obesity. They are less likely to conceive naturally and with fertility treatments, more likely to miscarry, and have more prematurity and other complications with their pregnancies. We describe the many causes, including key roles that a dysbiotic intestinal microbiome plays in metabolic derangements accompanying obesity, increased calorie absorption, and increased appetite and fat storage. Genetic causes are contributory if these other factors are present but have limited effect in isolation. The numerous health consequences of obesity are discussed. The authors itemize ways that an individual and societies can mitigate the pandemic. However, individual will power, the will of society to enact change, and willingness of the public to accept outside intervention frustrate efforts to stabilize or reverse this crisis. The most promising strategies are education and efforts by individuals to make responsible choices several times every day to protect, most effectively by prevention, their most valuable asset. (C) 2017 by American Society for Reproductive Medicine.