By. Dr. Kristi Maas, MD, FACOG
Diet and weight can be a sensitive topic, but when it comes to fertility, weight plays an important role. Individuals who are underweight or overweight had decreased fertility. Weight can be classified by a measurement called body mass index or BMI. This looks at your weight compared to your height where you divide your weight in kilograms by your height in meters. A BMI of less than 19 is considered underweight and BMI over 25 is considered overweight. BMI greater than 30 is considered obesity.
Being too thin can impact fertility and impair egg release (ovulation). One of the first signs can be irregular menstrual cycles (periods) or no cycles. Multiple factors signal our body that it is a suitable time and environment to reproduce. If our body perceives it is starving, this is not an optimal time for pregnancy given that calorie requirements increase in pregnancy. Even individuals with a normal weight can signal the body they are starving with restrictive dieting and/or eating disorders. In general, a woman must gain 2 pounds more than the weight at which she stopped having her period to resume menstruation. Individuals looking to gain weight should focus on healthy fats and complex carbohydrates, not high calorie simple carbohydrates. Studies suggest that individuals with a BMI <19 take four times a long to conceive than those with a normal BMI.
Being obese also impacts ovulation. Women with a BMI >30 are at an increased risk of having irregular or absent menstrual cycles. Even modest weight reduction of 5-10% in obese patients can be enough to restore ovulation. Weight reduction should be gradual and consistent at a max of approximately 2 pounds per week. Studies have shown that individuals with a BMI >35 take twice as long to conceive.
Tracking calories consumed and calories burned with a food and activity diary can help patients achieve their goal weight and maintain this weight for optimization of fertility. All individuals should achieve at least 150 minutes of exercise per week. Those looking to lower their BMI should increase this duration and those with a low BMI who already exercise above this may want to reduce their activity in addition to increasing their caloric intake. Working with a nutritionist and/or a personal trainer and discussing your goal weight with your doctor can help you optimize your fertility.