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High BMI Early Gestational Diabetes Test – Is It Really Needed?

Having a plus size pregnancy involves patient advocacy and making informed decisions, including whether to undergo a high BMI early gestational diabetes test.

Typically, during pregnancy, you'll have a standard glucose test for gestational diabetes between the 24th and 28th weeks of pregnancy.

Those with a Body Mass Index (BMI) over 30 and individuals at higher risk of developing gestational diabetes often get tested early on during pregnancy. Later on, they also undergo routine screening between 24 – 28 weeks.

With evidence shedding light on the lack of effectiveness of this early screening for those with a high BMI, many are wondering if it's a crucial precaution or an avoidable stressor during an already overwhelming time.

In this article, we'll unpack the latest research, weigh the pros and cons, and help you navigate this conversation with your healthcare provider.

Please note this article is not medical advice. It's intended to help you make an informed decision in consultation with your care team addressing your unique needs.

three glucose drinks for gestational diabetes testing

Gestational Diabetes

Before we address the high BMI early gestational diabetes test recommendation, let's review what gestational diabetes is and the typical testing protocol.

What is gestational diabetes?

Gestational diabetes arises from hormonal changes during pregnancy, linked to the placenta's role in sustaining pregnancy. The placenta, vital for the baby's growth, produces hormones that can make insulin less effective and can cause insulin resistance. This condition means your body requires more insulin than it can produce.

It's important to recognize that this form of diabetes isn't caused by any individual action. So, there's no need for self-blame. It is a physiological response where the body cannot cope with the increased demand for insulin production, and it typically resolves after giving birth.

People of all sizes can get gestational diabetes!

Realizing that gestational diabetes isn't a result of your actions can significantly reduce any feelings of guilt or stress that may come with the diagnosis. However, it's important to understand that while you didn't cause gestational diabetes, addressing it is essential for both your well-being and your baby's.

Gestational diabetes increases the risk of developing high blood pressure, preeclampsia, gestational hypertension, and the necessity for cesarean birth. Babies have an increased risk of being large for gestational age, having a premature birth, respiratory distress syndrome, and low blood sugar levels following birth.

Because of these increased risks, screening for gestational diabetes is considered a standard care practice for all pregnant individuals between the 24th and 28th weeks of pregnancy.

When someone has a gestational diabetes diagnosis, there are some next steps they'll want to take. Managing blood sugar levels becomes paramount. This management typically includes connecting with a maternal-fetal medicine specialist, monitoring nutrition, regular physical activity, and, potentially, medication.

What is the screening or testing for gestational diabetes?

While a few testing options are available when screening for gestational diabetes, such as the jelly bean test, the “two-step” screening method is the most common and recommended by the American College of Obstetricians and Gynecologists (ACOG).

The “two-step” screening method starts with a 1-hour glucose challenge test. If the results from this initial test raise concerns, the next step is to proceed with the Oral Glucose Tolerance Test (OGTT).

Glucose Challenge Test

Glucose Challenge Test (GCT)

This test involves drinking a sweet solution containing a measured amount of glucose. Blood is drawn one hour later to measure the glucose concentration in the bloodstream. Elevated blood sugar levels after the GCT may indicate potential issues with glucose metabolism and could lead to further testing.

Oral Glucose Tolerance Test (OGTT)

If the results of the GCT indicate elevated blood sugar levels, the next step is often the OGTT. Fasting is typically required for at least 8 hours before the OGTT. During the test, you drink a glucose solution, and blood is drawn at specific intervals (usually at 1-hour intervals for up to 3 hours). This is done to monitor how your body processes the glucose. If two or more of the subsequent blood glucose measurements during the OGTT exceed the normal range, it typically indicates gestational diabetes.

Glucose Challenge Blood Test

Please note, you might find suggestions on online forums about what to eat to “pass” the initial glucose test. However, as mentioned above, developing gestational diabetes does not reflect your character. Getting accurate results from this test is essential.

So, don't try to “cheat” this test because accurate results are vital for you and your baby's wellness.

High BMI Early Gestational Diabetes Testing

With an understanding of gestational diabetes and the testing procedure, let's explore the recommendation for early screening.

Early screening for gestational diabetes is recommended for individuals with specific risk factors, including a history of gestational diabetes, family history of diabetes, Polycystic Ovary Syndrome (PCOS), previous large babies, and advanced maternal age. 

The American Diabetes Association recommends testing everyone with a BMI greater than 25 (or 23 in Asian Americans) who have one or more risk factors for type 2 diabetes. 

In their latest committee opinion with guidelines for higher-weight individuals, ACOG states that early pregnancy screening for glucose intolerance (gestational diabetes or overt diabetes) should be determined by specific risk factors. These factors include a maternal BMI of 30 or greater, known impaired glucose metabolism, or previous gestational diabetes.

This recommendation is listed under their “C category,” meaning it's based primarily on consensus and expert opinion, not evidence. 

Although ACOG acknowledges that a high BMI is among the risk factors for considering early screening, many healthcare providers opt to conduct early testing based solely on BMI.

What does the research say

A high BMI is associated with an elevated risk of both diabetes and gestational diabetes. So, detecting early on if someone is prediabetic, diabetic, or has gestational diabetes enables timely interventions to monitor the well-being of the pregnancy.

While the rationale behind early screening is understandable, there is growing questioning regarding its necessity based only on BMI, particularly among individuals already aware of their A1C levels

So, let's look at the evidence! 

Early Gestational Diabetes Screening Research

The Harper et al. (2020) study is the first U.S. based randomized controlled trial examining the timing of gestational diabetes screening—early versus standard timing. 

The trial aimed to evaluate the efficiency of these screening times in real-world clinical settings rather than controlled research environments—a valuable approach!

The trial included 922 participants with a BMI of 30 or higher, all carrying a single baby, and excluded those with specific pre-existing conditions. 

Screening compared early (14-20 weeks) to routine (24-28 weeks) gestational diabetes testing, using the two-step screening method (explained above). It also involved testing for undiagnosed pre-pregnancy diabetes.

The main discovery from the research was that early gestational diabetes screening did not make a difference in lowering adverse perinatal outcomes. 

Adverse perinatal outcomes refer to complications that can occur during pregnancy or childbirth. So, despite being screened earlier, it didn't seem to improve the overall safety of pregnancy or childbirth.

The Harper trial even suggests potential risks associated with early gestational diabetes diagnosis. For example, higher medical intervention rates and possible adverse effects from over treatment.

Additionally, in 2021, the US Preventive Services Task Force concluded that there isn't enough evidence to recommend screening for gestational diabetes before 24 weeks in pregnant individuals who don't show any symptoms.

This aligns with the findings of the Harper et al. study, which also questions the effectiveness of early gestational diabetes screening. Together, these findings raise important questions about the necessity and timing of gestational diabetes testing, particularly for individuals with a high BMI.

Should you get tested early for gestational diabetes?

There's no definitive answer! Engaging in an open dialogue with your care provider is essential for determining what's best for you and your baby.

If your care provider suggests early screening, mainly based on your BMI, and you're uncertain, having an open conversation is crucial.

Start by asking questions to understand the rationale behind their recommendation and explore any concerns you may have. 

Think about asking:

  • What specific factors beyond my BMI suggest early testing in my situation?
  • Are there other tests or approaches that could provide similar insights?
  • What might a positive or negative result from early screening mean for my pregnancy journey?
OBGYN talking to a pregnant couple

The decision whether to undergo early testing for gestational diabetes is nuanced and multifaceted. While this article has provided insights into the considerations and research surrounding this topic, it's essential to remember that there's no one-size-fits-all answer. 

Each individual's circumstances, preferences, and medical history should guide the decision-making process. And seeking care from a size-friendly care provider who understands the unique needs during a plus size pregnancy can be invaluable. 

By having open communication with your care team and staying informed about emerging research, you can navigate this decision with confidence and ensure the best possible care for yourself and your baby.


Special thanks to Anna Bertone for her assistance with the research for this article.

Jen McLellan, CBE
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