How much weight should you gain in pregnancy? It is one of the most-asked questions in the prenatal clinic — and one of the most misunderstood. Healthy ranges are far narrower than the old "eat for two" advice suggested, and they depend heavily on your pre-pregnancy BMI, not how you feel mid-pregnancy. Here is the evidence-based breakdown using the Institute of Medicine (IOM) guidelines that obstetricians worldwide rely on.
How Much Weight Should You Gain? (IOM Chart by BMI)
The IOM publishes the most widely accepted recommendations. Find your pre-pregnancy BMI band and read across:
| Pre-pregnancy BMI | Category | Total gain (single baby) | Total gain (twins) |
|---|---|---|---|
| < 18.5 | Underweight | 12.5 – 18 kg (28 – 40 lb) | Not enough data — discuss with provider |
| 18.5 – 24.9 | Normal weight | 11.5 – 16 kg (25 – 35 lb) | 17 – 25 kg (37 – 54 lb) |
| 25 – 29.9 | Overweight | 7 – 11.5 kg (15 – 25 lb) | 14 – 23 kg (31 – 50 lb) |
| ≥ 30 | Obese | 5 – 9 kg (11 – 20 lb) | 11 – 19 kg (25 – 42 lb) |
Note: BMI is calculated from your weight before pregnancy. If you do not know your starting BMI, your provider can estimate it from your first prenatal visit weight.
Weight Gain Trimester by Trimester
First Trimester (Weeks 1–13): 0.5 – 2 kg
Most women gain very little — and many lose weight due to nausea and food aversions. This is normal. The baby is still tiny (about 6 cm at week 12), so calorie needs do not yet rise. Aim for steady hydration and prenatal vitamins rather than extra food.
Second Trimester (Weeks 14–27): roughly 0.4 kg per week
This is when most weight gain happens. Appetite returns, nausea usually fades, and the baby triples in length. A normal-BMI woman typically adds 5 to 7 kg over the second trimester. Add about 340 extra calories per day — equivalent to a glass of milk plus a peanut butter sandwich.
Third Trimester (Weeks 28–40): roughly 0.4 kg per week, slowing near the end
Gain continues at a similar pace, then often slows or plateaus in the final two weeks as the baby drops into the pelvis. Add about 450 extra calories per day. Some women lose 1 to 2 kg in the last week before labour — also normal.
The pattern, not the number: Steady gain matters more than hitting an exact total. A consistent 0.4 kg per week in T2 and T3 usually puts you exactly where you need to be by week 40.
Where Does the Weight Actually Go?
For an average normal-BMI woman gaining about 13 kg, the breakdown looks like this:
- Baby: 3.0 – 3.5 kg
- Placenta: 0.6 – 0.8 kg
- Amniotic fluid: 0.8 – 1.0 kg
- Larger uterus: 1.0 kg
- Increased breast tissue: 0.5 – 1.5 kg
- Extra blood volume: 1.5 – 2.0 kg
- Extra body fluids: 1.5 – 2.0 kg
- Maternal fat stores (for breastfeeding): 2.5 – 3.5 kg
Only about 25% of pregnancy weight is the baby itself — the rest is essential biology supporting it.
Twins and Multiple Pregnancies
Carrying twins requires significantly more weight gain — see the table above. Most providers recommend an extra 600 calories per day from the second trimester onwards for a twin pregnancy, plus higher protein, iron and folic acid. Triplet pregnancies are managed individually with a specialist.
When Weight Gain Is Too Slow or Too Fast
Always contact your provider if you gain more than 1.5 kg in a single week (especially in T3, with swelling or headaches — possible preeclampsia), if you have lost more than 5% of body weight in T1 (possible hyperemesis), or if you have not gained any weight by week 20.
Insufficient weight gain raises the risk of low birth weight, preterm birth and growth restriction. Excessive gain raises the risk of gestational diabetes, preeclampsia, large-for-gestational-age babies and difficulty losing weight postpartum. Both extremes are best caught early and corrected gently.
Healthy Habits for Steady Gain
- Quality over quantity. Whole grains, lean protein, dairy, fruit and vegetables fuel the baby with what it actually needs.
- Do not eat for two. The "extra meal" myth leads to 5 to 10 kg of unnecessary gain.
- Stay active. 150 minutes of moderate movement per week is the ACOG benchmark — see our safe pregnancy exercise guide →
- Hydrate. Thirst is often mistaken for hunger; aim for 2 to 2.5 litres daily.
- Track gently. Once-weekly weighing in the morning before breakfast gives the cleanest signal.
- Eat the rainbow. Different coloured fruits and vegetables provide different micronutrients — see the safe foods guide →
Your prenatal team will weigh you at every visit and flag any deviation early. Trust the process — and remember that pregnancy weight is doing important work.
Continue reading: Second Trimester Guide: Weeks 14–27 →
Frequently Asked Questions
How much weight should I gain in pregnancy if my BMI is normal?
If your pre-pregnancy BMI is between 18.5 and 24.9, the Institute of Medicine recommends a total weight gain of 11.5 to 16 kg (25 to 35 lb) over the full pregnancy.
Is it normal to lose weight in the first trimester?
Yes. Many women lose 1 to 3 kg in the first trimester due to morning sickness and food aversions. This is generally not harmful as long as you stay hydrated and the loss does not continue past week 14.
How much extra should I eat each day?
First trimester: no extra calories needed. Second trimester: about 340 extra calories per day. Third trimester: about 450 extra calories per day. That is roughly a sandwich and a glass of milk — far less than 'eating for two'.
Can I diet during pregnancy?
No. Restrictive dieting during pregnancy can deprive your baby of nutrients essential for brain and organ development. If you are concerned about excessive gain, focus on food quality and gentle activity rather than calorie cutting, and speak to your provider.
Why am I gaining weight so fast?
Sudden rapid weight gain (more than 1 kg in a week in the third trimester) can be normal water retention but can also signal preeclampsia, especially if paired with swelling in the hands and face, headaches or vision changes. Call your provider promptly.
How much weight do you lose right after birth?
Most women lose 5 to 7 kg in the first 24 hours — the baby, placenta, amniotic fluid and some excess body fluid. The remaining weight typically takes 6 to 12 months to come off with healthy eating and gradual activity.
Should I weigh myself every day?
Once a week, at the same time of day, in the same clothes is more meaningful than daily weighing. Daily fluctuations are mostly water and can be discouraging. Your provider will track the trend at every prenatal visit.