Don’t Let BMI Define Your Pregnancy

Pregnancy weight gain is at the forefront of nearly every pregnant person’s mind. But weight gain and your body mass index (BMI) do not have to define your pregnancy. Weight is an emotionally-loaded topic for many pregnant people, and providers know this. As a result, many providers struggle to talk with patients about healthy pregnancy weight gain, pregnancy risks associated with plus-sized pregnancies, or losing weight to improve fertility.

So, providers turn to body mass index (BMI) to avoid upsetting their patients. Using BMI allows them to standardize their approach to pregnancy weight gain and body size discussions. But is BMI really an accurate measure of how healthy a pregnant person is? Their chances for a healthy pregnancy? The best way to determine their pregnancy and delivery care plan? More and more providers, pregnant people, researchers, and advocates from the Health At Every Size (HAES) movement would answer emphatically, “No!” Learn more about how the maternity care system relies too heavily on BMI and how you can avoid letting your BMI define your pregnancy.

What is BMI?

Body mass index (BMI) is a calculation using height and weight to evaluate your body size. It is an indirect measurement only. Doctors calculate BMI by dividing your weight by your height squared: BMI = weight / height². It’s not a direct measurement, such as scanning your body with an X-ray, MRI, or calipers.

In 1998, at the height of the low-fat diet craze, the National Institutes of Health approved BMI as the standard measurement of health. With that, BMI officially became a health indicator, used to put people into underweight, ideal body weight, overweight and obese categories.

BMI is the default measure for obesity because it is the easiest and cheapest way to measure body fat. As a result, healthcare providers can easily put people into risk categories using the same measurement across a range of patients. In addition, researchers use BMI to track population-wide weight trends.

The Oversized Role BMI plays in Pregnancy Care

For example, researchers can look at the BMIs of many pregnant people to try to find associations between pregnancy outcomes and certain BMIs. Some research studies show that women with higher BMIs are more likely to have gestational diabetes, hypertensive disorders of pregnancy, or larger babies. Your provider then generalizes the results of these studies to your BMI and prescribes the recommended amount of “safe weight gain” for you during pregnancy.

But does your BMI accurately consider all your health conditions or risk factors? For example, how much do you exercise? What type of diet do you follow? What is your family history of high blood pressure or diabetes? Again, the answer is no when it comes to BMI. The Belgian mathematician Adolphe Quetelet developed BMI scales in 1832 using data from predominantly white European men to measure weight in different populations. Why are medical professionals still using charts based on white men of European origin from almost 200 years ago to decide the ideal weight you can gain during pregnancy or what kind of testing you should have? Good question.

BMI is a Flawed Indicator of Health, Especially In Pregnancy

There are many other problems and critiques of using BMI as a health indicator during pregnancy, such as:

• BMI can not be accurately calculated once you are pregnant. So providers use pre-pregnancy BMI – typically calculated at your first OBGYN appointment. But your weight and body composition may have already changed at this point, especially if you did not find out right away that you were pregnant or are struggling with hyperemesis and have lost weight due to constant nausea and vomiting.
• BMI scales do not take into account race or sex. At the same BMI, women have, on average, more body fat than men, and Asians have more body fat than whites. 
• BMI is imperfect; it does not distinguish between body fat and lean body mass. Muscle is denser than fat and weighs about 18 percent more. So a person could have a lean body mass (very little excess fat) but weigh more because they have lots of muscle. Their heavier body weight would skew their BMI, putting them in an “overweight” and higher-risk pregnancy range, even though their pregnancy could be perfectly healthy.
• People gain weight in different ways throughout their pregnancy. The recommended pregnancy weight gain categories based on BMI do not reflect this.
• BMI does not directly correlate with health (someone can have a high BMI and be healthier than a person with a lower BMI, for example). Recent studies of BMI and health indicators (blood sugar, cholesterol, and blood pressure) found that more than half of people considered overweight by BMI were healthy by these other indicators. 
• The location of your body fat may matter more to your health than how much body fat you have when it comes to health risks.
• The psychological damage caused by a pregnancy care provider telling a pregnant person they are overweight, obese, or have a high risk can cause physical and emotional stress and harm.

According to the American College of Obstetricians and Gynecologists (ACOG), there are significant risks associated with obesity and pregnancy. But how the provider talks about these risks with their plus-sized patients can be devastating, confusing, and downright harmful. In addition, many critics argue that continuing to use BMI to define a “healthy body” is racist and sexist because it is based solely on a white, male standard. A standard that does not reflect the current reality, which is that more than half of women in the U.S. begin pregnancy classified as overweight or obese based on BMI.

High-Risk Pregnancy Based on BMI, More Harm than Health

Using BMI in maternity care also perpetuates weight bias among maternity care providers, the health care system, and society. Weight bias can be unconscious or conscious. The current mindset of most care providers is women who are outside the normal BMI range aren’t a healthy weight and should be treated as though they are high risk. With the high-risk designation, pregnant people often have more appointments and testing. More appointments and testing add a time and financial burden to pregnant people. And all of this oversight sometimes leads to medical interventions that aren’t always needed. 

Being classified as a high-risk pregnancy can limit a person’s access to midwifery care, desired birth location, and type of birthing experience. While care providers set their own guidelines, the American College of Gynecologists and Obstetricians states that obesity is not an indication for the transfer of routine obstetric or gynecologic care. Birth centers and medical facilities may have BMI restrictions for the size of people who can deliver at the facility. Current maternity care deserts in more rural areas of the United States mean that plus-sized pregnant women may have to travel long distances and have limited choices for where, when, and how they deliver.

Plus-sized pregnant people are traumatized when selected medical facilities turn them away on account of their BMI. The bias baked into BMI (and using BMI to classify a pregnancy as high risk or low risk) contaminates the care provided. Most patients with an elevated BMI already report feeling stigmatized by healthcare providers.  This stigmatization leads patients with elevated BMIs to avoid care because they feel traumatized at each OB visit. Having to weigh themselves at every prenatal visit is just one example of traumatizing pregnancy experiences for plus-sized people.

Size-Inclusive Pregnancy Care Without BMI Bias

Critics of BMI and weight-biased maternity care argue that there is a better way to care for pregnant people. Researcher and author of Health At Every Size writes, “well-being and healthy habits are far more important than any number on the scale. Many maternity care providers and members of the anti-fat bias movement support applying the HAES model to pregnancy care.

Providers can help empower pregnant people from a strength-based perspective, supporting what people are already doing to stay healthy and feel good. This approach removes the stigma and avoids making people feel “broken” before they even start their pregnancy. It is more than likely that a plus-sized pregnant person has been told before that they need to lose weight. They have probably already tried countless diets or ways to lose weight. They do not need to be reminded of past struggles or setbacks. Many patients with an elevated BMI prefer not to use the word “obese” or “obesity.” You should feel comfortable asking your maternity care provider or other office staff not to use this terminology.

How You Can Prevent Your BMI from Defining Your Pregnancy

Unfortunately, there is no directory of size-friendly or HAES-certified maternity care providers yet. Until there is, here are some questions you could ask as you select your midwife or ob-gyn to help you find a more size-inclusive provider:

1. Do I have to be weighed at every prenatal visit? What other arrangements have you made for prior plus-sized patients?
2. If I have an elevated BMI, what does this mean for my pregnancy in terms of testing and prenatal visits during my pregnancy, my delivery plan, or care overall?
3. Have you heard of Health of Every Size (HAES)?
4. How do you support your pregnant patients with a history of disordered eating or are in larger-sized bodies that might be labeled as high risk?

Asking these questions will help you find a healthcare provider who will promote your individual health based on your individual needs. Your specific body has specific needs, especially during pregnancy. Talking to friends, colleagues, or family members about their weight-related pregnancy experiences will also give you an idea of more body-inclusive maternity care providers.

Find HAES-aware Support People and Providers

While the burden of teaching your doctor or nurse-midwife how to talk about weight and health or the HAES approach to pregnancy care should not fall on you, there are some ways for you to reduce some of the health hazards of an unhealthy focus on BMI. For example, working with a size-friendly nutritionist or dietician during pregnancy can help you navigate the challenges of eating well during pregnancy in any size body. Likewise, requesting a referral from your obstetrical provider to a size-friendly physical therapist can help you find ways to stay active and move your body injury-free through your pregnancy.

Continuing to use BMI as a standard part of pregnancy care perpetuates the painful and harmful stigmatization of plus-sized pregnant people. Change in the healthcare world does not come quickly and easily. While (very) slow changes in medical and nursing schools’ curriculum may eventually change tomorrow’s providers’ weight stigma, there are some steps you can now to limit how much BMI defines your pregnancy. Having a provider who you can trust and who makes you feel understood may be the most critical part of having a positive pregnancy and birth experience. If your provider’s weight bias or preoccupation with BMI does not make you feel safe or well-cared for, then you and your baby deserve better care.