**Abstract**

With increasing global obesity, there is a growing body of research looking at the impact of this on reproduction. Both male and female fertility are impacted on by being overweight or obese. Although the pathophysiology is not clear, it appears that obesity impacts endocrine function in men and women, oocyte and sperm quality, embryo quality, endocrine receptivity, and implantation. Miscarriage, pregnancy, and live birth rates and the risk of congenital malformations are all influenced by obesity. Transgenerational health is also affected, with metabolic, endocrine, and reproductive outcomes in the offspring being negatively affected by both paternal and maternal obesity. It appears that weight loss results in improvements in these outcomes and various strategies have been employed including lifestyle and behavior modification, pharmacological agents, and also bariatric surgery. This chapter aims to explore the reproductive outcomes of obesity and how this can be best managed to improve outcomes.

**Keywords:** obesity, IVF, embryos, bariatric, fertility, offspring, reproduction, lifestyle, oocyte, sperm

#### **1. Introduction**

Overweight or obesity is defined as an accumulation of excess body fat that poses a risk for health [1]. A measure often used in assessment of this is the body mass index (BMI), which is a person's weight in kilograms divided by height in meters squared (kg/m2 ). Obesity is a BMI greater than 30 and overweight is a BMI greater than 25, although in South East Asian populations, it is generally accepted that the upper limit of normal is a BMI of 23.

Globally, 39% of adults over 18 years are overweight and 13% are obese, and worldwide, obesity has tripled since the 1970s [2]. Being overweight or obese is directly linked to a greater risk of mortality and disease than being underweight.

Infertility is defined as failure to achieve a clinical pregnancy after 12 months or more of regular unprotected sexual intercourse [3]. Globally, at least 50 million couples worldwide experience infertility, with the burden affecting up to one in four couples in developing nations. The overall prevalence of infertility does not appear to have changed since the 1990s.

Overweight or obesity is understood to impact on both female and male reproductive health, and mounting research demonstrates that this impact will extend to the health and reproductive outcomes of future generations.
