Healthy Pregnancy Weight Gain by Trimester: IOM Guidelines
How much should you actually gain — and when? Here's what official guidelines say, broken down by starting weight and trimester.
Per Institute of Medicine (IOM) guidelines, recommended total pregnancy weight gain depends on pre-pregnancy BMI: underweight women should gain 28-40 lbs, normal weight 25-35 lbs, overweight 15-25 lbs, and obese 11-20 lbs. Twin pregnancies require significantly more gain across all categories.
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IOM Weight Gain Guidelines (Single Pregnancy)
| Pre-Pregnancy BMI | Category | Recommended Total Gain |
|---|---|---|
| Below 18.5 | Underweight | 28–40 lbs |
| 18.5–24.9 | Normal Weight | 25–35 lbs |
| 25.0–29.9 | Overweight | 15–25 lbs |
| 30.0+ | Obese | 11–20 lbs |
Source: Institute of Medicine (IOM), endorsed by ACOG and the CDC.
Weight Gain Pattern by Trimester
Most weight gain occurs in the second and third trimesters. A typical pattern for normal-weight women: roughly 1-5 lbs total in the first trimester (weeks 1-13), then approximately 1 lb per week through the remainder of pregnancy.
Twin Pregnancy Guidelines
Twin pregnancies require notably more weight gain to support both babies. For normal-weight women, IOM suggests 37-54 lbs total — significantly higher than the 25-35 lb range for single pregnancies.
What If You're Outside the Range?
These are population-level guidelines, not strict rules. Individual factors — including pre-existing health conditions, multiples, and nutritional needs — mean your healthcare provider may recommend a different target specific to your situation.
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