Obesity decreases the chances that a woman will get pregnant, and the more obese she is, the worse her prospects of conception, said a Dutch report, looking at the relationship between fertility and obesity of women and their body mass index, a ratio of weight to height. Women with a BMI of 30 or higher are considered obese, and had significantly lower probability of becoming pregnant naturally as compared to women who has a BMI of between 21 to 29.