How much weight should you gain during pregnancy? The answer depends on your pre-pregnancy BMI. The Institute of Medicine (IOM) published evidence-based guidelines in 2009 that remain the gold standard worldwide.
Too little weight gain raises the risk of preterm birth and low birth weight. Too much increases the risk of gestational diabetes, cesarean delivery, and childhood obesity. The right range protects both mother and child.
IOM 2009 Guidelines by BMI Category
First, calculate your pre-pregnancy BMI. This determines which category applies to you:
| Pre-pregnancy BMI | Category | Recommended gain |
|---|---|---|
| < 18.5 | Underweight | 12.5 – 18 kg |
| 18.5 – 24.9 | Normal weight | 11.5 – 16 kg |
| 25 – 29.9 | Overweight | 7 – 11.5 kg |
| ≥ 30 | Obese | 5 – 9 kg |
Twin pregnancies
For twins, the IOM recommends a higher total weight gain:
How Does Weight Gain Distribute Over Weeks?
Weight gain does not happen evenly. In the first trimester (up to week 13), most women gain very little — often just 0.5 to 2 kg. Most of the gain happens in the second and third trimesters.
As a rough guide for normal-weight women after the first trimester: about 0.35–0.50 kg per week. For overweight: 0.23–0.33 kg/week, for obese: 0.17–0.27 kg/week.
| Category | 1st trimester | 2nd/3rd trimester (per week) |
|---|---|---|
| Underweight | ~1–2 kg | ~0.44–0.58 kg |
| Normal weight | ~1–2 kg | ~0.35–0.50 kg |
| Overweight | ~0.5–1 kg | ~0.23–0.33 kg |
| Obese | ~0.5–1 kg | ~0.17–0.27 kg |
Calculate your personal recommendation
IOM-based weight gain calculator — free and no sign-up required.
Calculate for free now →Where Does the Extra Weight Come From?
The weight gained during pregnancy is not just the baby. For a total gain of 12 kg, approximately:
Common Questions
What if I'm outside the recommended range?
Individual fluctuations are normal. What matters is the trend over several weeks. Talk to your OB-GYN if you notice significant deviations.
Do these guidelines apply to everyone?
The IOM guidelines are evidence-based recommendations for healthy singleton and twin pregnancies. Individual conditions like gestational diabetes or hypertension may require different targets.
Does water retention count toward weight gain?
Yes. Mild swelling in legs and feet is normal and part of the recommended gain. Sudden severe swelling should be assessed by a doctor.
Conclusion
Recommended pregnancy weight gain depends on your pre-pregnancy BMI. Use our Pregnancy Weight Gain Calculator to get your personalized recommendation — and check your BMI with the BMI Calculator. Find your due date and current week with the Pregnancy Calculator.
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