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Is BMI Enough to Determine a Healthy Weight Gain?

Katlyn Joy |10, October 2013


Pregnancy can be a time of confusing mixed messages. You've heard of eating for two, but magazine covers blast mothers for gaining too much weight one week, then criticize others for looking mommy-rexic the next. You want to do the right thing, but is it that easy to know the right thing?

In 2009 new guidelines were issued by the Institute of Medicine (IOM), on how much weight pregnant women should gain. These were the first updates in nearly two decades. The IOM noted significant shifts in pregnant women in that time period such as a much greater number of women having multiple pregnancies and a significant rise in overweight or obese women conceiving.

They IOM noted that to determine how much weight a woman should gain is to look at her pre-pregnancy weight. Thus, the group took a woman's BMI or body mass index as a means of evaluating a woman's weight recommendations for pregnancy. The IOM also cautioned that a single number cannot take into account a woman's age or race, or other possibly significant factors, so a weight range is given.

These recommendations include a rate of weight gain as well as a range of weight. The IOM also cautions in its "Report Brief: Weight Gain During Pregnancy," about using the information along with your medical provider. The IOM states in its report, "The guidelines and supporting recommendations are intended to be used in concert with good clinical judgment and should include a discussion between the woman and her care provider about diet and exercise."

Limitations of BMI

How accurate a health portrait does a BMI number yield? There are definite limitations.

Here's a caveat offered by the National Institutes of Health, "[the BMI] does have some limits. It may overestimate body fat in athletes and others who have a muscular build. The BMI also may underestimate body fat in older people and others who have lost muscle."

So if you begin pregnancy with a higher proportion of muscle than the average woman, you may receive a BMI that indicates you should lose weight when a mirror and common sense will tell you otherwise.

Additionally, many health experts tout another tool as being a better predictor of health than the BMI. The Cleveland Clinic website recommends the waist-to-height ratio as a superior method of determining a healthy weight.

To determine your waist-to-height ratio, simply use a tape measure and measure your waist and height. Your waist circumference should be less than half your height, keeping both figures in inches for ease of calculation. Be sure not to suck in your gut, but relax and keep it real and measure level around your belly button.

Being Proactive

Don't just rely on your health care provider guiding you on weight management issues during your pregnancy, either. According to researchers at Penn State College of Medicine, a December 2012 study found that "overweight women are not receiving proper advice on healthy weight gains or appropriate exercise levels during their pregnancies."

The researchers hypothesized that many doctors were uncomfortable talking to patients about being overweight and when women saw multiple practitioners in a medical practice they may even have received conflicting advice on eating or exercise.

However, the American Congress of Obstetricians and Gynecologists has recommended that women be counseled on the maternal and fetal risks of obesity in pregnancy, including such things as:

  • Birth defects
  • Difficulty seeing organs during sonograms due to excessive maternal fat layers
  • Gestational diabetes
  • Pre-eclampsia
  • Emergency c-sections
  • Hemorrhaging post-labor
  • Bladder and kidney infections
  • Stillbirth
  • Babies too large for gestational age

Advice for Pregnant Women

You are not a number. You are an individual and each of your pregnancies is different as well. You want to be as healthy as possible and you cannot rely on doctors and midwives to advise and inform you. You need to be aware of your diet, your weight and your rate of weight gain, your fitness level and activity level. To accomplish this:

  • Know your numbers, such as your BMI and your waist-to-height ratio
  • Advise your doctor of your fitness level and physical activity level prior to getting pregnant
  • Ask your physician at each visit what your weight is, how much you gained since your last visit and if this seems appropriate.
  • Find out your health care providers recommendations on exercise in your pregnancy.
  • Be aware of any rapid weight changes as these can indicate a serious problem.
  • Understand there is no magic number; there are healthy ranges and special considerations such as the weight and health level you were at when your conceived, your age, your build, your pregnancy especially if you are carrying multiples, for instance.
Katlyn Joy is a freelance writer with a Master's of Arts in Creative Writing. She is mom to seven children and lives with her family in Denver, Colorado.

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