Body Mass Index (BMI)

Definition - What does Body Mass Index (BMI) mean?

Body mass index (BMI) is a body composition measurement that estimates body fat. The estimation is obtained by a calculating weight in kilograms (kg) divided by height in meters (m) squared:

(kg) / [height (m)]2 = BMI

BMI is not a direct measurement of body fat and is used as a screening tool to determine general weight categories: underweight, healthy weight, overweight, and obese. BMI estimates for adults (both men and women) fall into the following categories:

  • Underweight is a BMI below 18.5
  • Acceptable weight is from 18.5 to less than 25
  • Overweight is 25 and above (includes obese)
  • Obese is 30 and over.

The overall composition of body fat can have an influence on overall health and fertility.

FertilitySmarts explains Body Mass Index (BMI)

Maintaining a healthy body weight and BMI is important for overall health as well as fertility. Both women and women who are found to be either underweight, overweight, or obese, according to their BMI may have difficulty conceiving or carrying a pregnancy full term.

Women who are considered underweight according to BMI may not be getting the nutrients their body needs to ovulate regularly. Women who are overweight according to their BMI may see an increase in insulin levels that can cause their ovaries to produce male hormones (androgens) and stop releasing eggs (anovulation), affecting ovulation.

Men's fertility is also affected by BMI. Obesity in men affects fertility due to imbalances in hormone regulation causing low sperm count and decreased sperm movement making it difficult for sperm to reach the egg.

A BMI considered underweight or overweight can also affect the success of fertility treatments. In patients who are not a healthy body weight complications may include lower response to medication used to induce ovulation, more difficulty retrieving eggs, higher risk of pregnancy loss, and a higher risk of complications during pregnancy.

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