**5.1 Body mass index (BMI)**

Obesity is defined as BMI equal to or more than 30. According to the WHO, more than 1.9 billion adults of the world population are suffering from the extra body mass (BMI >25), and more than 650 million are obese [124].

A significantly lower ongoing pregnancy rate and implantation rate in obese women have been reported [125, 126]. The implantation rate, pregnancy and live birth rate are shown to be lower in obese women with the tendency to progressively go down with each unit of BMI (kilograms per square meter) [127]. It has been also found that higher BMI is associated with lower clinical pregnancy rates especially in women under age 35 using their own oocytes [128].
