Pregnancy weight gain by trimester
By Pregora Editorial Team · Updated 2026-04-26 · 7 min read
Healthy pregnancy weight gain isn't evenly distributed across the three trimesters. The Institute of Medicine (IOM) 2009 guidelines — endorsed by ACOG and used worldwide — recommend only 1-4.5 lb (0.5-2 kg) in the entire first trimester, then steady weekly gain in the second and third.
Total recommended weight gain by BMI category
| Pre-pregnancy BMI | Total gain (singleton) | Total gain (twins) |
|---|---|---|
| Underweight (<18.5) | 12.5–18 kg / 28–40 lb | No specific recommendation |
| Normal weight (18.5–24.9) | 11.5–16 kg / 25–35 lb | 17–25 kg / 37–54 lb |
| Overweight (25–29.9) | 7–11.5 kg / 15–25 lb | 14–23 kg / 31–50 lb |
| Obese (≥30) | 5–9 kg / 11–20 lb | 11–19 kg / 25–42 lb |
Use our pregnancy weight gain calculator for personalised ranges based on your height, pre-pregnancy weight, and current week.
First trimester (weeks 1-13): 1-4.5 lb total
The first trimester sees minimal weight gain — typically 1-4.5 lb (0.5-2 kg) across the entire 13 weeks. Many women actually lose a small amount of weight due to morning sickness and food aversions.
What's gaining weight in the first trimester:
- Increased blood volume
- Breast tissue development
- Uterine growth
- Placenta formation
The baby itself is tiny in the first trimester (~28 grams / 1 ounce by week 13), so you're not "eating for two" yet. Stick to your normal calorie intake — possibly even a bit less if morning sickness reduces appetite.
Second trimester (weeks 14-26): ~1 lb/week
The second trimester is when weight gain accelerates. For normal-weight women, the IOM recommends approximately 0.42 kg (~0.9 lb) per week on average. Total second trimester gain: ~12 lb / 5.5 kg.
Weekly rates by BMI:
- Underweight: 0.51 kg / 1.1 lb per week
- Normal: 0.42 kg / 1.0 lb per week
- Overweight: 0.28 kg / 0.6 lb per week
- Obese: 0.22 kg / 0.5 lb per week
You should add about 340 calories/day in the second trimester (above your pre-pregnancy needs) — equivalent to a yoghurt + a piece of fruit + a slice of toast, not a giant meal.
Third trimester (weeks 27-40): ~1 lb/week, slowing near term
The third trimester continues at the same weekly rate as the second — about 1 lb per week for normal-weight women. However, gain often slows in the final 2-4 weeks as appetite reduces (baby pressing on stomach) and water retention plateaus.
What's gaining weight in the third trimester:
- Baby (most rapid growth — 0.5 lb/week from 28 weeks)
- Amniotic fluid (peaks around week 36)
- Uterus (continues expanding)
- Maternal fat stores (energy reserves for delivery + breastfeeding)
- Placenta (final size)
Add about 450 calories/day in the third trimester — but listen to your body. Some women feel less hungry as space tightens.
Where does the weight actually go?
For a normal-weight woman gaining 30 lb total, the breakdown is approximately:
- Baby: 7-8 lb
- Maternal fat & nutrient stores: 6-8 lb
- Increased blood volume: 3-4 lb
- Increased fluid retention: 2-3 lb
- Larger breasts: 1-3 lb
- Placenta: 1.5 lb
- Amniotic fluid: 2 lb
- Larger uterus: 2 lb
So roughly half the gain is the baby + supporting tissues, and half is maternal stores that drop off after delivery and breastfeeding.
What if I'm gaining too much or too little?
If your gain is consistently outside the IOM range, talk with your provider. Possible adjustments:
- Diet review (focus on nutrient density vs. calories)
- Activity adjustment (gentle exercise is encouraged in pregnancy)
- Screening for gestational diabetes if rapid weight gain
- Screening for preeclampsia if sudden weight gain + swelling
Don't try to lose weight while pregnant unless specifically directed by your provider — caloric restriction can harm fetal development.
Disclaimer: IOM guidelines are population averages. Your provider may recommend different targets based on your individual situation, health history, or pregnancy complications.