BMI and Pregnancy: The Number That Doesn't Tell the Whole Story

If you've ever been pregnant with a higher BMI, chances are you've encountered it: the raised eyebrow at a booking appointment; the assumption that your pregnancy will be high-risk; the feeling that a number on a chart has somehow become more important than the person sitting in front of the healthcare professional.

As both an antenatal educator and someone who has personally experienced pregnancy with a higher BMI, I know how overwhelming this can feel. I've sat on both sides of the conversation. I've experienced the anxiety that can come from hearing statistics and risk discussions, and I've supported countless parents navigating the same journey.

So let's talk about what BMI actually means, what the evidence tells us, and why informed decision-making matters so much during pregnancy.

What is BMI?

Body Mass Index (BMI) is a calculation based on height and weight. It was originally developed as a population-level tool to study health trends, not as a tool to predict the health of an individual person.

While BMI can identify patterns across large groups of people, it has significant limitations:

• It does not distinguish between muscle and fat.

• It does not measure fitness levels.

• It does not assess nutrition, lifestyle, or overall health.

• It does not account for ethnic differences in body composition.

• It cannot tell us how healthy a particular pregnancy will be.

Despite these limitations, BMI remains widely used in maternity care, and across all kinds of medical settings.

Does a Higher BMI Increase Pregnancy Risks?

The short answer is yes—but the conversation is often far more nuanced than it is presented.

Research shows that, on average, women with a higher BMI have an increased likelihood of certain complications, including:

• Gestational diabetes

• Hypertensive disorders such as pre-eclampsia

• Blood clots

• Caesarean birth

• Shoulder dystocia

• Stillbirth

These risks are real and should be discussed honestly. However, risk does not equal certainty. And it's very worthwhile pointing out that women with BMI's in the normal and underweight range can also experience these complications too.

Many (and that's most!) women with higher BMIs experience healthy pregnancies, straightforward births, and healthy babies. The vast majority do not experience every complication listed on a consent form.

Understanding the difference between relative risk and absolute risk is crucial. For example, if a risk doubles from 1 in 1,000 to 2 in 1,000, that sounds alarming when described as "twice the risk." Yet 998 out of 1,000 people will still not experience that outcome. Numbers matter. Context matters more. And using these terms with your medical provider is important to ensure that their recommendations are not being served with a side of bias.

The Problem with Weight Bias in Pregnancy Care

One of the most significant challenges faced by women with higher BMIs is not necessarily the increased medical risks—it's the bias they encounter.

Research consistently shows that weight stigma exists within healthcare settings.

Women report:

• Feeling judged at appointments

• Having symptoms attributed solely to weight

• Receiving less respectful care

• Feeling pressured into interventions without fully understanding their options

• Avoiding healthcare due to previous negative experiences

No pregnant person should feel ashamed of their body. Shame does not improve outcomes. Respectful, evidence-based care does. Every pregnant person deserves clear information, compassionate support, and the opportunity to make informed decisions about their care.

My Own Experience

I've had pregnancies with a higher BMI. I know what it feels like to see that number highlighted in your notes. I know what it feels like to wonder whether healthcare professionals see you as a person first or a BMI category first. What I learned through those experiences is that informed decision-making is powerful. Understanding the evidence allowed me to ask questions, "weigh" up (pun not intended) recommendations, and make decisions that felt right for me and my family.

That experience now shapes the way I teach. When parents attend my antenatal classes, I want them to leave understanding not only what recommendations may be offered during pregnancy and birth, but why those recommendations exist, what the evidence says, and what choices they have.

I still remember the eyebrows heading for the hairline of the midwife who did my booking appointment on baby #2. She hadn't even looked at me, was crunching the numbers, and then announced that I needed to have a consultation with the anaesthetist, because I would 'more than likely need a section' on account of my BMI. The anaesthetist then told me I should get an epidural as soon as possible so that I wouldn't have to have a general anaethetic, despite me stating in no uncertain terms that I planned to avoid both an epidural and a caesarean. Cue me bawling my eyes out, and him looking rather uncomfortable. In essence, I was made to feel like my body would fail me before it even had a chance to do the test.

You Deserve Information, Not Fear

However, pregnancy is not a exam, and certainly pass-fail one. It's not about having the "perfect" BMI, the "perfect" birth plan, or the "perfect" pregnancy.

It's about understanding your options, knowing your rights, and making informed decisions that align with your values. Whether your BMI is 20 or 40, you deserve maternity care that is respectful, personalised, and evidence-based. You deserve to be treated as a whole person, not a statistic.

Preparing for an Informed Birth

One of the best ways to reduce fear in pregnancy is through education. In my antenatal classes, we explore:

• Understanding risk and statistics

• Making sense of pregnancy recommendations

• Birth physiology

• Induction of labour

• Caesarean birth

• Pain relief options

• Breastfeeding preparation

• Newborn care

• Informed consent and decision-making

My goal isn't to tell you what choices to make.

It's to help you understand your options so you can make the choices that are right for you.

If you're pregnant and want to feel informed, confident, and prepared for birth and early parenting, I'd love to support you.

Book your antenatal class today here and start your journey towards a more informed and empowered birth experience.

If you would like to read more about BMI and pregnancy research, I suggest also reading anything and everything that Dr. Sara Wickham writes on it. She's the MVP in this arena

Aoife xx