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BMI Calculator for Pregnancy

author image Kristeen Cherney
Kristeen Cherney began writing healthy lifestyle and education articles in 2008. Since then, her work has appeared in various online publications, including Healthline.com, Ideallhealth.com and FindCollegeInfo.com. Cherney holds a Bachelor of Arts in communication from Florida Gulf Coast University and is currently pursuing a Master of Arts in English.
BMI Calculator for Pregnancy
Looking down onto a pregnant woman's belly as she stands on a scale. Photo Credit adrian825/iStock/Getty Images

BMI, which stands for body mass index, is a calculation used based on your weight and height. The goal of such a calculation is to see if you are within the proper weight range for your height. Accurate weight measurements are critical, especially when you are pregnant in order to ensure optimum health for you and your baby. The March of Dimes reports that BMI is most useful before and after pregnancy.


BMI is typically used at a primary care checkup to determine whether you are at an appropriate weight for your height. To calculate your BMI, first determine your weight in pounds. Then multiply your height in inches twice. Divide your weight into this number and then multiply it by 703. According to the March of Dimes, a normal BMI is considered to be between 18.5 and 24.9. Underweight is below 18.5, overweight is 25 to 29.9, and an obese BMI reading is 30 and above.

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Recommended Weight Gain

Women’s Health breaks down the weight gain recommendations by trimester, with 4 lbs. recommended during the first trimester and 3 to 4 lbs. per month during the duration of your pregnancy. However, the amount of weight you should gain varies depending upon your BMI before pregnancy. The Centers for Disease Control, also called the CDC, recommends that underweight women gain 28 to 40 pounds during pregnancy while women with a BMI of 26 to 29 gain 15 to 25 pounds. Obese women with a BMI of 29 or higher should gain approximately 15 pounds. The CDC explains that a woman within a normal BMI range of 19.8 to 26 should gain between 25 and 35 pounds during pregnancy.

Risk Factors

According to the CDC, underweight pregnant women can have babies pre-term or have babies with low birth weights. The March of Dimes reports that overweight and obese women can have delivery complications that can result in death. The risk of delivering an overweight baby also increases. Having a high BMI during pregnancy also puts you at risk of developing gestational diabetes, hypertension and pre-eclampsia.


Whether you have a low or high BMI before pregnancy, it is imperative that you follow your doctor’s recommended weight gain guidelines in order to lower potential risk factors that can affect you and your baby. If you are overweight, do not attempt to lose weight during pregnancy as this can developmentally harm your baby. Eat balanced healthy meals while pregnant and avoid processed foods. Exercises like swimming and walking are also imperative to healthy weight maintenance and endurance. If you are underweight and fail to gain enough weight, your doctor may recommend that you increase your daily calories.


Obesity among women varies by state, most likely because of the types of food eaten in a given region. The March of Dimes reports that pre-pregnancy obesity is most common in southern states, Texas and Alaska. If you gain too much weight during pregnancy and your baby is born healthy, your personal risk factors may still be prevalent. According to Women’s Health, women who give birth and do not drop the extra weight gained during pregnancy within six months after giving birth are at a higher risk of being obese.

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