The ranges follow the 2009 Institute of Medicine (now National Academy of Medicine) guidelines, also used by ACOG and the CDC. They depend on your BMI before pregnancy: underweight (under 18.5) 28-40 lb (12.5-18 kg); normal weight (18.5-24.9) 25-35 lb (11.5-16 kg); overweight (25-29.9) 15-25 lb (7-11.5 kg); obese (30 and over) 11-20 lb (5-9 kg). The first trimester usually adds only 1-4.5 lb (0.5-2 kg); after that the advised weekly gain is about 1 lb (0.4 kg) per week if underweight, 0.8-1 lb if normal, 0.5-0.7 lb if overweight and 0.4-0.6 lb if obese. For twins the guideline totals are 37-54 lb (17-25 kg) for normal weight, 31-50 lb (14-23 kg) for overweight and 25-42 lb (11-19 kg) for obese; there is no firm advice for underweight twin pregnancies. The week-by-week figure on this page is a straight-line estimate for a single baby from those rates.
| Pre-pregnancy BMI | One baby | Weekly gain (2nd and 3rd trimester) | Twins |
|---|---|---|---|
| Under 18.5 (underweight) | 28-40 lb (12.5-18 kg) | 1 lb (0.51 kg) | No firm guideline |
| 18.5-24.9 (normal) | 25-35 lb (11.5-16 kg) | 0.8-1 lb (0.42-0.57 kg) | 37-54 lb (17-25 kg) |
| 25-29.9 (overweight) | 15-25 lb (7-11.5 kg) | 0.5-0.7 lb (0.28-0.38 kg) | 31-50 lb (14-23 kg) |
| 30 and over (obese) | 11-20 lb (5-9 kg) | 0.4-0.6 lb (0.22-0.33 kg) | 25-42 lb (11-19 kg) |
It depends on your weight before pregnancy. For a normal BMI (18.5-24.9) the guideline is 25-35 lb (11.5-16 kg) with one baby; less if you started overweight and more if you started underweight.
Usually only 1-4.5 lb (0.5-2 kg). Many people gain nothing or even lose a little because of morning sickness.
After the first trimester, about 1 lb (0.4 kg) per week for underweight, 0.8-1 lb for normal weight, 0.5-0.7 lb for overweight and 0.4-0.6 lb for obese starting BMI, for one baby.
Roughly 7-8 lb is the baby, with the rest split between the placenta, amniotic fluid, larger uterus and breasts, extra blood and fluid, and fat stores. It is an approximate breakdown and varies.
General information only, not medical advice. These are population guidelines, and your doctor or midwife may advise a different range for you.
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