CALCULATING BODY MASS INDEX
Body Mass Index (BMI) is a means to determine if a person is overweight, underweight, or normal weight, based on
their weight for height. The BMI determination assists with recommendations regarding weight gain during pregnancy.
Following is the BMI mathematical formula (please note there are different ways to express this formula):
Weight in pounds
Height in inches ÷ Height in inches x 703 = BMI
BMI Mathematical Formula: Weight in pounds divided by height in inches divided by height in inches multiplied by 703
equals BMI.
GUIDELINES FOR USE OF PRENATAL WEIGHT GAIN CHART
1. Calculate the prenatal woman’s Body Mass Index (BMI), using the BMI mathematical formula. In the information box
in the upper left corner of the form, record the name, height, pre-gravid BMI, pre-gravid weight, and delivery date
(EDC).
2. WIC Certifier, CPA or Nutritionist calculates the completed weeks gestation using the gestation (pregnancy) wheel.
3. Calculate the number of pounds gained or lost to date. Indicate number of pounds lost or gained by +/- sign when
recording in the Weight Change column.
4. Determine the prenatal woman’s recommended weight gain channel (recommended total weight gain range in
pounds), according to the woman’s pre-pregnancy weight group and Body Mass Index (BMI) on the following table
[Adapted from National Academy of Science’s Institute of Medicine (IOM) 1990, Nutrition During Pregnancy ]:
Pre-pregnancy
Pre-pregnancy
Recommended Total Weight Gain
Weight Group
Body Mass Index (BMI)
Ranges for Pregnant Woman (pounds)
Underweight
<19.8 BMI
28 - 40 lbs.
Normal Weight
19.8 to 26.0 BMI
25 - 35 lbs.
Overweight
26.1 to 29.0 BMI
15 - 25 lbs.
Obese*
>29.0 BMI
At least 15 lbs.
* Women in the Obese Pre-Pregnancy Weight Group do not have a recommended weight gain channel, but rather a
recommended weight gain of at least 15 pounds.
5. WIC
Certifier, CPA or Nutritionist highlights on the graph the recommended weight gain channel. Notice the
variations in the shading of the weight gain channels. Some of the channels overlap slightly. These shaded areas
follow the recommended weight gain channel throughout a 40-week, full-term singleton pregnancy.
6. The informational box represents the information required at each of the prenatal woman’s bimonthly (or monthly, if
high risk) weight checks during the course of her pregnancy. Record the date, weight, weight change and weeks
gestation each time her weight is measured and plotted. Initials of the person taking (and/or recording) the
measurements should also be indicated.
7. Plot the weight gain/loss on the graph. The vertical axis represents Prenatal weight gain in pounds. The horizontal
axis represents week’s gestation. Mark a dot at the intersection of the two lines. Circle the dot to signify the plot
mark. Do not put a date by the dot indicating when the measurement was taken.
*Weight gain does not need to fall on a graphed line; rather the rate and pattern of gain parallel to the line should
be monitored.
MO 580-0001 (05-05)
NS-11