Your BMI

BMI is a measure for indicating nutritional status in adults. We calculate body mass index by dividing a person’s weight in kilograms by the square of their height in metres (kg/m2). For example, an adult who weighs 70 kg and whose height is 1.75 m will have a BMI of 22.9 (70 /1.75 x 1.75) = BMI 22.9 (11).

BMI is easy to calculate, and as such, is the most commonly used tool to assess health risk in the broad population. Like other measurement scales, it is not perfect. It accounts only for weight and height and lacks details such as sex, muscle mass and age. In some people it overestimates the body fat; in others it underestimates. Waist circumference measurements can complement BMI estimates and improve their accuracy.

The ideal BMI (18.50 – 24.99) is the range which evidence suggests has the least amount of fat-related risks associated with it. A BMI either below or above this range has associated health risks. At least 2.8 million people around the world die each year as a result of being overweight or obese.

Women are more likely to be obese than men, with obesity among women being approximately double that among men in some countries. While ‘rich’ countries are most likely to have obesity in higher numbers, low-income earners in those countries have higher BMI’s than people with high incomes. Women who are overweight or obese are at higher risk of;

  • high blood pressure,
  • high cholesterol and triglycerides
  • insulin resistance,
  • coronary heart disease,
  • ischemic stroke,
  • type 2 diabetes,
  • infertility,
  • pregnancy loss,
  • breast, colon, uterine, kidney and gallbladder cancer.
18.5 – 24.99Normal range
25 – 29.99Overweight
30 – 34.99Obese class I
35 – 39.99Obese class II
40 or higherObese class III

Waist circumference

Where your fat is on your body can be an important sign of your risk of developing ongoing health problems. Putting fat on around your midsection carries more danger than if you put it on your hips and thighs. Checking your waist circumference before pregnancy is a simple way to tell if you are carrying excess fat around your middle. Regardless of how tall you are, an adult’s woman’s waist measurement of 80 cm or over is an indication of higher than healthy levels of internal fat deposits. These can coat the heart, kidneys, liver, digestive organs and pancreas, and the risk of heart disease and stroke.

Measuring your waist helps to assess the risk of diseases related to body fat by estimating how much fat you carry around your middle (12). Women are sometimes more relaxed about their weight during pregnancy. This approach may be because many women are unaware of the recommended weight gain during pregnancy and the impact their pre-pregnancy BMI can have. The Institute of Medicine (IOM) guidelines have published recommendations for weight gain in pregnancy based on a woman’s pre-pregnancy weight.



Dr Janelle McAlpine (PhD), Clinical Midwife
Photo by gpointstudio, used under license from