Why Do Some Women Get Gestational Diabetes, While Others Don’t?

From hmri.org.au

• Gestational diabetes (GDM) is a pregnancy-specific condition that causes elevated blood sugar levels due to a complex mix of pregnancy hormones, genetics, and lifestyle factors.
• The placenta produces hormones that naturally increase insulin resistance during pregnancy, but in some women this resistance becomes excessive, leading to diabetes.
• GDM isn’t simply about lifestyle choices – some women are genetically predisposed regardless of their health, and researchers are still investigating why it affects some women but not others.

 It’s a diagnosis that can come as a surprise. One day you’re navigating morning sickness and nursery paint swatches, the next you’re being told you have gestational diabetes, a condition that only occurs during pregnancy. But what determines whether a woman develops it or not? 

“There’s no clear answer, but it’s a combination of lifestyle, genetics and the complex role of pregnancy hormones, particularly those released by the placenta,” explains University of Newcastle Professor Kirsty Pringle, who leads the Placental Biology and Pregnancy Research Group at Hunter Medical Research Institute (HMRI). 

Gestational diabetes (GDM) is characterised by elevated blood glucose levels that develop during pregnancy and usually disappear after birth. Unlike type 1 or type 2 diabetes, it isn’t a lifelong condition, but it can carry serious short and long-term risks for both mother and baby. It is also increasingly common. 

The hormone factor 

At the centre of it all is the placenta, a temporary organ that supports the growing baby throughout pregnancy. Among its many functions, the placenta produces hormones that make the mother’s body more resistant to insulin. This is a normal part of pregnancy, meant to ensure the baby receives a steady supply of glucose.

“Pregnancy itself is an insulin-resistant state,” says Professor Pringle. “Your cells are less sensitive to insulin, so glucose stays in your bloodstream longer. In healthy pregnancies, this helps nourish the baby.” 

But in some women, this insulin resistance goes too far. “Some of the hormones that are released by the placenta cause insulin resistance. If they’re unbalanced, you can get too much insulin resistance and that’s what tips you over into diabetes.” 

The reason this hormonal balance happens in some women and not others is not always clear, but researchers suspect genes could play a role. 

A genetic component 

While a healthy diet and weight are important, GDM isn’t simply the result of poor lifestyle choices. Some women are more predisposed than others, even if they’re otherwise healthy. Factors like maternal age, previous GDM diagnoses, and even your ethnic background can play a role. 

“There’s some genetic component as well that can increase your risk,” says Professor Pringle. “We can get what are called single nucleotide polymorphisms, little mutations in the genes of those hormones, which means they’re not working as effectively.” 

Women with a family history of diabetes are particularly vulnerable. “If you’ve got someone in your close family like a sibling or parent who has type 2 diabetes then you’re more at risk.” 

Lifestyle and weight 

That said, lifestyle still plays a significant role. Entering pregnancy at a higher weight or gaining weight too rapidly in early pregnancy are both known risk factors.  

But even women who make major health changes aren’t immune. “While lifestyle changes do help, they don’t guarantee anything.” 

Professor Pringle emphasises that becoming healthier still matters. “Even if you do still develop gestational diabetes, it likely won’t be as severe or carry as many potential consequences for the baby. So being your healthiest self is definitely still recommended.” 

The mystery of small babies 

While most babies born to mothers with GDM are larger than average due to the excess glucose, Professor Pringle is researching an unusual pattern where some babies are actually smaller. 

“There is some evidence that there’s damage to the vessels in the placenta, which means not enough nutrients are being transported across,” she says. “What is going on in those placentas is something I’m still investigating.” 

This variation highlights just how complex the condition is and how much researchers are still learning. 

Can it be prevented? 

For women hoping to reduce their chances of developing GDM, the best strategy is to optimise health before pregnancy. 

“Being the healthiest possible before you try to conceive is the best approach,” Professor Pringle advises. “Once you’re pregnant, it’s not about losing weight, it’s about managing weight gain in a healthy way.” 

She points out that weight gain during pregnancy should be individualised. “Women who are overweight according to their Body Mass Index (BMI) when they start the pregnancy don’t need to gain as much. It’s not a one-size-fits-all.”  

Eating well, staying active, and working with healthcare professionals to monitor weight and blood sugar levels can all help reduce risk but they’re not guarantees. 

“Some women will do everything right and still develop it. That’s why we need to keep researching.” 

What happens after diagnosis? 

Gestational diabetes is manageable and treatment usually starts with lifestyle changes.

“Once you’re diagnosed, there are different management options,” says Professor Pringle. “In the first instance, we usually try diet modification and exercise to try and maintain your blood glucose levels.” 

If those steps aren’t enough, medication may be considered. “Women can also have insulin during pregnancy, or metformin is the other treatment that’s used,” she explains. 

But insulin or metformin is only prescribed if diet and exercise don’t keep blood sugar in check. Gestational diabetes typically resolves after birth meaning women can usually stop taking medication. 

The bottom line 

Why do some women develop gestational diabetes and others don’t? The answer lies in a complex mix of genetics, hormones, weight, age and ethnicity, but they don’t tell the whole story. 

“There’s still a lot we don’t know,” Professor Pringle says. “But the more we understand about how pregnancy hormones interact with insulin, and why that affects some women and not others, the better we can care for mothers and babies.” 

Gestational diabetes is more than just a blood sugar issue. It’s a window into the powerful, intricate systems that sustain pregnancy and how fragile that balance can be. 

https://hmri.org.au/news-and-stories/why-do-some-women-get-gestational-diabetes-while-others-dont/