How to use it
- Choose metric or US units and enter your weight and height from before you were pregnant.
- Choose one baby or twins and set your current week.
- Read the total gain recommended for the whole pregnancy, the weekly rate after the first trimester and the range expected by now.
How it works
Your pre-pregnancy BMI (weight in kg divided by height in metres squared) decides the group, using the usual WHO limits: below 18.5, 18.5 to 24.9, 25 to 29.9 and 30 or more. The 2009 Institute of Medicine guidelines then give the total gain for a pregnancy with one baby:
| Pre-pregnancy BMI | Total gain | Weekly gain, 2nd and 3rd trimester |
|---|---|---|
| Under 18.5 | 12.5 – 18 kg (28 – 40 lb) | 0.44 – 0.58 kg |
| 18.5 – 24.9 | 11.5 – 16 kg (25 – 35 lb) | 0.35 – 0.50 kg |
| 25 – 29.9 | 7 – 11.5 kg (15 – 25 lb) | 0.23 – 0.33 kg |
| 30 and over | 5 – 9 kg (11 – 20 lb) | 0.17 – 0.27 kg |
The first trimester is expected to add only 0.5 to 2 kg (1.1 to 4.4 lb). For twins the report gives provisional totals only: 17 to 25 kg, 14 to 23 kg and 11 to 19 kg for healthy weight, overweight and obesity.
Worked example
You weighed 60 kg and are 165 cm tall: BMI = 60 ÷ 1.65² = 22.0, a healthy weight, so the total is 11.5 to 16 kg. At week 20, 7 of the 27 weeks after week 13 have passed, which is 7 ÷ 27 of the remaining gain. The range is 0.5 + 11 × 7/27 = 3.4 kg to 2 + 14 × 7/27 = 5.6 kg.
Good to know
- The guidelines are for the pre-pregnancy BMI, not your weight today.
- Women under 18 were treated separately in the research and may need other advice.
- Weight on the scale includes the baby, placenta, fluid and your own changes, so it is not all “fat”.
- This is general information, not medical advice. Your midwife or doctor can set a target that fits your health, and should be told about sudden gain, swelling or weight loss.