How much weight should you gain in pregnancy?
The right amount depends on your weight before pregnancy. The guidelines of the Institute of Medicine (2009), also used by the American College of Obstetricians and Gynecologists, set a total gain for each BMI group. Most of it comes after the first trimester: about 1 to 4.4 lb (0.5 to 2 kg) in the first 13 weeks, then a steady gain each week until birth.
Recommended total weight gain
- Underweight (BMI below 18.5): 28 to 40 lb (12.5 to 18 kg)
- Normal weight (BMI 18.5 to 24.9): 25 to 35 lb (11.5 to 16 kg); twins 37 to 54 lb
- Overweight (BMI 25 to 29.9): 15 to 25 lb (7 to 11.5 kg); twins 31 to 50 lb
- Obese (BMI 30 or more): 11 to 20 lb (5 to 9 kg); twins 25 to 42 lb
Example: a woman 5 ft 6 in tall who weighed 140 lb before pregnancy has a BMI of 22.6, a normal weight. At 20 weeks she should have gained about 7.3 to 12.3 lb, on the way to 25 to 35 lb in total.
Where the weight goes
At birth, only about 7 to 8 lb is the baby. The rest is the placenta, amniotic fluid, a larger uterus and breasts, extra blood and fluid, and some fat stored for breastfeeding.
Frequently asked questions
Is it a problem to gain more or less?
Gaining too much raises the risk of gestational diabetes, high blood pressure and a large baby; gaining too little raises the risk of a small baby and preterm birth. Your doctor or midwife can help you stay on track.
How many extra calories do I need?
None in the first trimester for most women, about 340 a day in the second and about 450 a day in the third.
What about twins and an underweight BMI?
There is no official guideline for twins when the BMI before pregnancy was under 18.5. Your care provider will set a target.