Obesity causes many hormonal changes triggered by excess body fat. This means that reproductive hormones are often out of balance when someone is obese. In women, this can mean irregular periods with less frequent ovulation, which decreases fertility. Compared to women with a normal body mass index (BMI), obese women are up to three times more likely to experience infertility. But when you lose even a small amount of weight, your fertility can improve. If you have infertility problems due to your weight, you may have a boost in fertility after weight loss surgery. That might be good news if you want to get pregnant. But unless you use effective birth control, you may also be more likely to get pregnant, even if you’re not trying.