How much weight should you gain in pregnancy?
It depends on your BMI before pregnancy, not your weight now. These are the Institute of Medicine (IOM 2009) guidelines:
| Pre-pregnancy BMI | Total gain | Per week (after week 13) | Twins |
|---|---|---|---|
| Underweight (below 18.5) | 12.5–18 kg | 0.44–0.58 kg | No guideline |
| Normal (18.5–24.9) | 11.5–16 kg | 0.35–0.5 kg | 17–25 kg |
| Overweight (25–29.9) | 7–11.5 kg | 0.23–0.33 kg | 14–23 kg |
| Obese (30 or more) | 5–9 kg | 0.17–0.27 kg | 11–19 kg |
In the first 3 months (to week 13) the gain is small — about 0.5 to 2 kg — and most of it comes in the second and third trimesters.
Example
You are 160 cm and weighed 60 kg before pregnancy: BMI = 60 ÷ (1.6 × 1.6) = 23.4 (normal), so the recommended gain is 11.5–16 kg. By week 24 a healthy gain is about 5–7.7 kg, a weight of roughly 65 to 67.7 kg. If you weigh 66 kg, you have gained 6 kg — within the range.
If you are 165 cm and weighed 85 kg, your BMI is 31.2 (obese) and the recommended gain is only 5–9 kg; by week 30, about 3.3–6.4 kg.
Why the right gain matters
Gaining too little is linked with a baby born small or early; gaining too much is linked with a large baby, a higher chance of caesarean birth, and more weight kept after birth. That is why you are weighed at every check-up.
How the weekly range is worked out
For the first 13 weeks the calculator spreads the first-trimester gain (0.5–2 kg) evenly, then increases steadily until it reaches the recommended total at week 40. The weekly rate this gives is close to the guidelines’ rates (for a normal BMI about 0.41–0.52 kg a week against 0.35–0.5), and it reaches the recommended total exactly.
Frequently Asked Questions
Is the gain measured from my pre-pregnancy weight or my first visit?
From your weight just before pregnancy. If you don’t remember it, use the weight from your first visit in the first trimester, which is usually close.
Should I eat for two?
No. ACOG says you usually need no extra calories in the first trimester, about 340 extra a day in the second and about 450 in the third. You can check your baseline needs with the calorie calculator; what matters most is a varied diet.
I have gained more than recommended — should I diet?
Don’t diet to lose weight during pregnancy without your doctor’s supervision. Talk to them; they will help you adjust eating and activity safely.
Why did I lose weight early in pregnancy?
Nausea and vomiting in the first months can cause a small loss, which is common. If vomiting is severe or you can’t keep food or drink down, see your doctor.
When does the weight come off after birth?
A large part is lost at birth and in the following weeks, and breastfeeding can help. When you want to check your weight later, use the BMI calculator.
Sources
- Institute of Medicine (IOM) 2009: Weight Gain During Pregnancy: Reexamining the Guidelines.
- MSD Manual: Guidelines for Weight Gain During Pregnancy (with ACOG recommendations).