One of the easiest ways to determine if you are underweight or overweight is to calculate your body mass index (BMI). There are many tables available online (search term: BMI table). Enter your height and weight into the tool to see your BMI.
A BMI between 19 and 24 is considered normal; less than 19 is considered underweight. A BMI between 25 and 29 is considered overweight and greater than 30 places you in the category of obese.
WEIGHT AND FERTILITY
Many underweight, overweight, and obese women have no problem getting pregnant. But others will have problems conceiving, most often due to ovulation problems (failure to release eggs from the ovaries).
A BMI of 18.5 or less (underweight) often causes irregular menstrual cycles and may cause ovulation to stop altogether. A BMI of 17.5 or less could indicate an eating disorder. Women at less than normal BMI should work with their doctor to understand the cause of this situation, and develop strategies to correct it.
A BMI in the obese range may also lead to irregular menstrual cycles and ovulation. However, even obese women with normal ovulation cycles have lower pregnancy rates than normal weight women, so ovulation isn’t the only issue. A visit to a health- care professional before becoming pregnant can help identify other disorders related to obesity that impact pregnancy such as thyroid disease, insulin resistance, and diabetes.
There is good evidence that obesity lowers the success rates of in vitro fertilization (IVF). Studies have shown lower pregnancy rates and higher miscarriage rates in obese women. Obese women are at an increased risk for developing pregnancy-induced (gestational) diabetes and high blood pressure (pre-eclampsia). Obese women also have a higher chance of delivering by cesarean section. Children of obese mothers are at increased risk of some birth defects and miscarriages.
MALE OBESITY AND INFERTILITY
Obesity in men may be associated with changes in testosterone levels and other hormones important for reproduction. Low sperm counts and low sperm motility (movement) have been found more often in overweight and obese men than in normal-weight men.
Changing your diet and lifestyle (for example, exercise) combined with a program that may provide group support is an effective step, but not always the appropriate first step if your age or your BMI is above 40. Weight loss surgery (bariatric surgery) is the most effective treatment for weight loss in women with a BMI greater than 40.