In plain words
Body mass index, or BMI, is a rough measure that compares weight to height. It is calculated by dividing weight in kilograms by height in meters, squared. In adults, a result of 18.5 to 24.9 is in the usual healthy range, 25 to 29.9 is overweight, and 30 or more is obesity. In pregnancy, BMI is recorded before or early in pregnancy, and it is used to set guidance on how much weight gain is typical. Clinicians also know its limits. BMI does not measure body fat directly, and it can miss differences in muscle and body shape. It is one number among several that a provider may look at. After birth, BMI may come up in talks about recovery and health, but it says nothing about how a mother is doing as a whole.
The deeper version
BMI equals weight in kilograms divided by height in meters squared. The WHO and CDC use cut-offs of 18.5, 25, and 30 kg/m2 for adult classification. A WHO expert consultation (2004) proposed lower cut-offs for Asian populations, at about 23 for overweight and 27.5 for obesity, reflecting higher adiposity at a given BMI. Prepregnancy BMI underlies the Institute of Medicine's 2009 ranges, which are set by category: underweight, normal, overweight, and obese. BMI correlates with adiposity but poorly identifies body composition in individuals, with limitations in athletes, older adults, and people with high muscle mass or short stature. Postpartum BMI reflects weight retained from pregnancy along with fluid and tissue changes that can take months to resolve. Debate continues over whether waist measures or other indicators should complement BMI in practice.
Where it comes up
- Weight gain in pregnancyPregnancy: Your Body
- Your body after birth: weight, shape, and timelinesPostpartum: Your Body
- Returning to exercisePostpartum: Your Body
- Gestational diabetesPregnancy: Your Body
What mothers here say about body mass index
No one has posted under this term yet.
Sources
- Institute of Medicine (now National Academy of Medicine) — Weight Gain During Pregnancy: Reexamining the Guidelines, 2009
- World Health Organization Expert Consultation — Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. The Lancet, 2004