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Obesity and Pregnancy


How might a high BMI affect your pregnancy?

Body Mass Index (BMI) is a measure based on your weight (kg) divided by your height (m)2. A high BMI can increase health risks during pregnancy. A BMI of 30.0 or more is classified as obese.

Most pregnant women have healthy babies—and that includes women who have a BMI of 30 or more. But being very heavy does increase the chance of problems.

Babies born to mothers who have a BMI of 30 or more have a higher risk of:

  • Birth defects, such as a heart defect or neural tube defects.
  • Being too large. This can cause problems during labour and delivery.

Mothers who have a BMI of 30 or more have a higher risk of:

If you're not pregnant already, having a BMI of 30 or more can make it hard to get pregnant.

But if you have a BMI of 30 or more, you can do a lot to improve your chances of having a healthy pregnancy.

Work with your doctor or midwife to get the care you need. Go to all your doctor visits, and follow your doctor's or midwife's advice about what to do and what to avoid during pregnancy.

Should you try to lose weight during pregnancy?

No. Pregnancy is not the time to lose weight. Your baby needs you to eat a well-rounded diet. Don't cut out foods or go on any type of weight-loss diet.

How much weight should you gain during pregnancy?

Experts recommend that women who have a BMI of 30 or more gain about 5 kg (11 lb) to 9 kg (20 lb). Your doctor will work with you to set a weight goal that's right for you. In some cases, a doctor may recommend that a woman not gain any weight.

Although pregnant women often joke that they're "eating for two," you don't need to eat twice as much food. In general, pregnant women need to eat about 340 extra calories a day in their second trimester. Women in their third trimester need to eat about 450 extra calories a day.footnote 2 You can get about 340 calories in a peanut butter sandwich. Having a cup of 1% milk with a peanut butter sandwich is about 450 calories.

How much can you eat during pregnancy?

How much you can eat depends on:

Like any pregnant woman, you need to eat a variety of foods from Canada's Food Guide. You especially need to make sure to get enough calcium and folic acid.

You may want to work with a dietitian to help you plan healthy meals to get the right amount of calories for you.

How will your prenatal care change if you have a BMI or 30 or more?

You will have the same number of doctor or midwife visits as a woman of average weight, unless you start to have problems. Then you would see your doctor or midwife more often. But you'll have the same type of tests to look for problems and make sure your baby is healthy.

What can you do to have a healthy pregnancy?

The best things you can do to have a healthy pregnancy are to eat a variety of foods, get regular exercise, avoid alcohol and smoking, and go to your doctor or midwife visits. If you didn't exercise much before you got pregnant, talk to your doctor or midwife about how you can slowly get more active.

If you're not pregnant yet, what can you do to get ready for pregnancy?

If you're not yet pregnant, now is a good time to try to lose some weight. Losing even 2 or 5 kilograms (5 or 10 pounds) may help reduce your risk for problems.

You also can make other lifestyle changes to get a future pregnancy off to a good start. These include getting enough folic acid, avoiding alcohol and smoking, and avoiding or limiting caffeine. See your doctor or midwife for a checkup before you become pregnant.

Some women may want to have weight-loss surgery. If you're thinking about it, talk with your doctor or midwife to learn how it might affect a future pregnancy.



  1. Public Health Agency of Canada. (2021). Your guide to a healthy pregnancy. Government of Canada. Accessed August 16, 2021.
  2. Kaiser LL, Campbell CG (2014). Practice paper: Nutrition and lifestyle for a healthy pregnancy outcome. Journal of the Academy of Nutrition and Dietetics, 114(7): 1099-1103. Accessed November 16, 2017.


Adaptation Date: 2/24/2022

Adapted By: Alberta Health Services

Adaptation Reviewed By: Alberta Health Services

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