Ensuring that your BMI (body mass index) stays healthy will keep your reproductive cycle in balance. According to Sydney Axelrod, MS, RD a registered dietician at Mount Sinai in New York City, weight is one of the most influential factors when it comes to fertility. "Being underweight can switch off your body's ability to reproduce eggs, as it senses there isn't enough fat to sustain a healthy pregnancy," she explained. "And being overweight can increase ovulatory infertility by 25 percent, which can lead to high-risk pregnancies with a probability of developing preeclampsia and gestational diabetes."