The purpose of this article is to provide evidence-based information about obesity stillbirth risks. This article is not medical advice.
It's critical that plus size people connect with size-friendly care providers and make decisions during pregnancy they feel are in the best interest of their baby and body.
Obese Pregnancy Risks – Stillbirth
People of size frequently report feeling shamed or judged in their medical care, especially when it comes to conception and pregnancy. It's sometimes hard to know how much a care provider’s personal bias influences the information and advice they give to a plus-size patient.
Plus size people do face increased risks, which is why open and honest communication between the patient and care provider is so important. When conversations about treatment leave the patient feeling ashamed or silenced, critical information may not be communicated. That’s not safe for anyone.
“My doctor told me I'm at a high risk for having a stillbirth and I should have an induction. My BMI is 35, and I'm so scared I'm going to lose my baby.” – Sarah
Sarah, who has a BMI of 35 and is concerned she is at “high risk” for a stillbirth with her baby.
What is the real risk when it comes to obesity stillbirth risks?
Current research tells us that people with a BMI of 20 experience around 40 stillbirths per 10,000 pregnancies—a risk that can also be expressed as 0.4% or 4 stillbirths per 1,000 pregnancies. The research also tells us that this risk rises by 78% for people of Sarah’s BMI.
That number sounds extremely high! So what does being 78% more likely to experience a stillbirth mean?
First, it’s important to understand that this percentage is known as a relative risk—which means it is a rate compared to another rate. Knowing a relative risk can be helpful, but we also need to know the actual numbers we are talking about (called the absolute risk).
In this case, Sarah’s absolute risk of having a stillbirth is 72 per 10,000, or 0.7%. This means there are around 7 stillbirths per 1,000 pregnancies for someone of Sarah’s BMI.
So, at a higher BMI, her risk rises from 4 to 7 stillbirths per 1,000 pregnancies. Can you see how knowing the real number—the absolute risk–gives us a much different picture than knowing the relative risk of 78%?
These figures refer to the overall risk of stillbirth after 20 weeks of gestation.
Obesity Stillbirth Risks And Induction
Research shows that, in general, the risk of stillbirth goes up after 39 weeks. I’ll dive deeper into this research below. First, I want to provide tools you can use if a care provider makes a recommendation for induction, because of a person's size, as this is happening more often.
The Bishop Score helps determine if your obstetric situation, including your cervix, is favorable for having a vaginal birth with an induction.
Along with the Bishop Score, a care provider must receive your informed consent before they can perform a procedure. This isn't merely you saying you agree, but it’s also key that you have a full understanding of the procedure, including the risks and benefits.
If a care provider recommends you consent to an induction, you can ask them a set of questions called the BRAIN Acronym.
B – What are the benefits?
R – What are the risks?
A – What are the alternatives?
I – Always listen to your intuition!
N – What happens next or if we do nothing?
Save the image below to your phone, so you can easily access these questions at any time.
I hope you find these two tools beneficial in making the decision you feel is best.
Obesity Stillbirth Research
I hired a researcher to dive deep into obesity stillbirth risks. Some of the information below might be overwhelming. Remember to address any questions or concerns with your care provider.
We'll begin with the systematic review and meta-analysis by Aune et al. (2014) published in JAMA. They examined 18 studies in their analysis of maternal BMI and stillbirth risk, including over 16,000 stillbirths among 3,288,688 participants. Stillbirth was defined differently across the included studies but generally meant the death of a fetus at 20 completed weeks or more of gestation.
They found that the association between BMI and stillbirth is mostly linear. This means that the risk of stillbirth goes up at a steady rate with increasing BMI. Rather than starting with an increased risk at the lowest BMIs, or jumping up in risk above a certain BMI point.
Since the relationship is mostly linear, we can say that for every 5-unit increase in BMI, the risk of stillbirth increases by 24%. So, for example, someone with a BMI of 30 is 24% more likely to experience a stillbirth during their pregnancy than someone with a BMI of 25. When the researchers looked specifically at stillbirths that occurred before the start of labor, they found a 28% increase in risk for every 5-unit increase in BMI. They did not find any increase in risk for stillbirths that occurred during labor.
This study uses people with a BMI of 20 as the reference group (compares their risk to all of the other BMI groups).
For example, people with a BMI of 30 have a 46% increased risk of stillbirth during pregnancy compared to people with a BMI of 20. That is their relative risk. Among people with a BMI of 30, there are estimated to be 59 stillbirths per 10,000 pregnancies. That is their absolute risk.
Chart showing relative risk vs. absolute risk.
% Increase above BMI 20
|[Reference]||9%||20%||32%||46%||61%||78%||97%||2.2 x the risk|
Number of stillbirths per 10,000 pregnancies
Informed consent and refusal discussion should include all of this information. Let’s talk about Sarah again. With a BMI of 35, Sarah is being pressured to have an induction at 39 weeks with no other medical indications. Her care provider is using this study as the basis for the recommendation.
She should be informed that people with “normal” BMI experience around 40 stillbirths per 10,000 pregnancies. This means that they experience about a 0.4% chance of stillbirth during pregnancy. This can also be expressed as a risk of 4 stillbirths per 1,000 pregnancies.
Since Sarah’s BMI is 35, it means that she is 78% more likely to experience a stillbirth during pregnancy. This is compared to someone with a BMI of 20. However, her absolute risk of stillbirth is 72 per 10,000 (a relatively low number).
That can also be expressed as a 0.7% chance of stillbirth or 7 stillbirths in 1,000 pregnancies.
It’s also important to remember that these figures refer to the overall risk of stillbirth after 20 weeks of gestation, not after reaching early or full term. The risk of stillbirth for everyone—regardless of BMI—rises gradually after 39 weeks and then increases more quickly at 42 weeks.
There are also other factors that may increase the risk of stillbirth that should be included in the informed consent discussion around non-medically indicated induction (see the Evidence Based Birth handout on Due Dates for a detailed list).
Of course, the conversation should also include the potential risks (side-effects) of induction as well as the potential benefits of induction.
The new Kawakita et al. (2017) study can help to inform people with BMIs greater or equal to 40 of the potential benefits of induction.
Kawakita et al. (2017) just published the first study to ever examine non-medically indicated induction of labor in morbidly obese people (BMI greater or equal to 40). Researchers looked back at the medical records of 1,894 first-time mothers and 2,455 experienced mothers who were considered to be morbidly obese. Of these, 22.7% of the first-time mothers and 32.2% of the experienced mothers had non-medically indicated inductions.
They found that for the first-time mothers, non-medically indicated induction at early term was associated with decreased risks of babies born >4,000 g (2.2% vs. 11.0%) compared with waiting for labor to begin (expectant management). At full term, non-medically indicated induction was associated with decreased NICU admission (5.1% vs. 8.9%). There was no increase in cesareans with non-medically indicated induction. In experienced mothers, non-medically indicated induction at early term was associated with a decreased risk of babies born >4,000 g (4.2% vs. 14.3%). At full-term, non-medically indicated induction was associated with a decreased risk of cesarean (5.4% vs. 7.9%).
There is a new clinical tool developed by Trudell et al. (2017) to predict the risk of stillbirth. It can’t perfectly tailor the risk estimate to each individual. It can at least take some important factors into account, such as maternal age, parity, race, smoking status, etc.
Final Thoughts On Obesity Stillbirth Risks
I hope this information helps you to understand the increased risk of having a stillbirth when you have a higher BMI. As stated from the start, people need to make decisions during pregnancy they feel are in the best interest of their baby and body.
If you're concerned about obesity stillbirth risks, be sure to have an open and honest conversation with your care provider. Here’s a helpful free guide on how to connect with a size-friendly provider – My Size Friendly Care Providers Guide
This is a lot of sensitive information that could prove triggering to some people questioning stillbirth risks when you're obese. While it’s important to know your increased risks, remember that most plus size people have healthy outcomes during pregnancy and birth.
Aune, D., Saugstad, O. D., Henriksen, T., & Tonstad, S. (2014). Maternal body mass index and the risk of fetal death, stillbirth, and infant death: a systematic review and meta-analysis. JAMA, 311(15), 1536-1546. doi:10.1001/jama.2014.2269
Kawakita, T., Iqbal, S. N., Huang, C. C., & Reddy, U. M. (2017). Nonmedically indicated induction in morbidly obese women is not associated with an increased risk of cesarean delivery. Am J Obstet Gynecol, 217(4), 451.e451-451.e458. doi:10.1016/j.ajog.2017.05.048
Trudell, A. S., Tuuli, M. G., Colditz, G. A., Macones, G. A., & Odibo, A. O. (2017). A stillbirth calculator: Development and internal validation of a clinical prediction model to quantify stillbirth risk. PLoS ONE, 12(3), e0173461.
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