A woman’s weight can affect her fertility. We know that at both extremes—very thin and obese—that there can be disruption of the normal process of regular, consistent ovulation. Anovulation can often result. Medications can be used to induce ovulation in these women in an attempt to become pregnant.

Body mass index, or BMI, is an index of a person’s relative “skinniness or heaviness.” The BMI factors in a person’s weight and their height to give an overall “index.”

A High BMI Indicates Obesity
 Normal body weight is BMI between 18.5 – 24.9
 A BMI under 18.5 indicates that the person is “underweight”
 A BMI of 25.0 – 29.9 indicates that the individual is “overweight,” but not obese
 A BMI over 30 indicates obesity
 A BMI over 40 indicates extreme obesity
Obesity is associated with increased risk for several serious disease processes.
Extreme obesity is associated with a dramatically increased risk for many serious
diseases.
How BMI is Calculated
 weight (in kilos) divided by height (in meters) squared
Therefore, if someone weighs 100 kilos and is 1.8 meters tall, their BMI is 100 divided
by 1.8 X 1.8 = 100/3.24 = 30.9.
To convert from pounds to kilos, take the weight in pounds and divide it by 2.2.
To convert from inches to meters, take the height in inches times 0.0254.
View a BMI table showing how to get your BMI from your height and weight.
Some recently published studies have shown a relationship between BMI and in vitro
fertilization success rates. We have reviewed other IVF data and found that increased
body weight (BMI > 30) has a significant negative effect on IVF pregnancy success
rates.
Bottom Line

If you are overweight (BMI over about 28) and having trouble getting pregnant, try to
lose weight. If you have irregular menstrual cycles (anovulation, or irregular ovulation)
and you are overweight, weight loss might make your cycle regular, thereby making you
more fertile.
If you are obese (BMI of 30 or higher) and are interested in IVF, you might have a
significantly improved chance for success if you reduce your weight before going
through the procedure.
Body Weight and Safety of IVF Procedures
Another issue related to body weight and IVF is safety for the patient at the egg retrieval
stage. As can be seen in ultrasound images, when a woman is significantly overweight,
the ovaries are usually pushed up “high,” away from the top of the vagina by the extra
fatty tissue that is in the pelvis.
At the time of IVF, the needle is pushed in vaginally to reach the eggs in the ovaries. If
the ovaries are too high, it will not be safe or easy get the needle into the follicles to get
the eggs out.
Another problem is that the ultrasound images become very “fuzzy” from the extra
tissue between the probe and the ovary. Therefore, it is often difficult to clearly visualize
the ovaries and the egg-containing follicles.