If you're too thin, meaning that you have a body mass index (BMI)
under 19, your body may not contain enough fat for you to ovulate normally. Studies show that you could take four times longer to conceive than a woman with a normal BMI. Being overweight, on the other hand (having a BMI over 25), can change the way your body fat processes hormones, raising your levels of male hormones, which can interfere with fertility. The ideal BMI for conceiving a child is 21-24. If you're overweight, though don't despair. Losing even a few pounds, (5 to 10 percent of your body weight) can make a significant difference in your fertility, according to Dr. Soules. Keep your spouse fit, too; excess fat in men can cause reduced sperm count and low testosterone levels. A BMI of 18 to 24 is great for him.