What can help prevent gestational diabetes?

Women are generally advised to eat a balanced diet during pregnancy. This means making sure you have a varied diet rather than eating a lot of the same type of food, so the baby gets all the nutrients he or she needs. Most women can simply trust their appetite and don’t need to follow a special diet.

According to the research done so far, the only women who benefit from dietary changes are those who are overweight or obese. They can lower their risk of gestational diabetes by changing their diet with the help of a professional dietitian or nutritionist. The dietary changes can reduce their blood sugar levels and help them put on less weight in pregnancy. In women who have a normal weight, dietary changes don't have a preventive effect.

Research has shown the following for women who are overweight ( BMI > 25) or obese ( BMI > 30):

• If they didn’t change their diet, 16 out of 100 women were diagnosed with gestational diabetes.
• If they did change their diet, 6 out of 100 women were diagnosed with gestational diabetes. 

But the studies didn't provide any information about whether the change in diet also influenced the child's birth weight, reduced the risk of complications during the birth, or helped to avoid the need for Cesarean sections.

Because carbohydrates increase your blood sugar levels, people are usually advised to cut down on carbohydrates (“carbs”) while making sure they still get enough fiber, and generally eat a balanced diet otherwise. Other common advice includes eating three not-too-big main meals and two to three smaller meals per day.

The exact dietary changes to be made will depend on things like how much the woman weighs and how much exercise she gets. Getting special advice from a dietitian or nutritionist can help to avoid adverse effects. It's important to make sure that your body gets enough calories and certain nutrients in pregnancy. So it isn't a good idea to go on a reduced-calorie diet while pregnant.

Women who gain a lot of weight in pregnancy have a higher risk of certain health problems and complications during childbirth. Putting on a lot of weight can be a sign of gestational diabetes. There are official recommendations concerning how much weight pregnant women should gain. This depends on how much they weighed beforehand.

• For women who were underweight before pregnancy ( BMI of less than 18.5): between 12.5 and 18 kilograms of weight gain during pregnancy.
• For women who had a normal weight before pregnancy ( BMI of between 18.5 and 24.9): between 11.5 and 16 kilograms of weight gain during pregnancy.
• For women who were overweight before pregnancy ( BMI of between 25 and 29.9): between 7 and 11.5 kilograms of weight gain during pregnancy.
• For women who were obese before pregnancy ( BMI greater than 30): between 5 and 9 kilograms of weight gain during pregnancy.

Research suggests that dietary supplements containing myo-inositol might reduce the risk of gestational diabetes. One possible explanation for this potential effect is that myo-inositol can make insulin work better. But it's not clear whether taking myo-inositol supplements can also reduce the risk of the possible consequences of gestational diabetes, such as complications during the birth. The women in the studies took 2 g of myo-inositol once a day, from the first trimester of pregnancy until the birth of their child. Most of them were overweight.

It is thought that having a vitamin D deficiency can increase the risk of gestational diabetes. But it's not clear whether taking vitamin D supplements has a preventive effect.

Certain dietary supplements, such as omega 3 fatty acids (fish oil), are sometimes claimed to help prevent gestational diabetes. But when omega 3 fatty acids were tested in studies, no preventive effect was found. There is a lack of research on the use of probiotics in this area.

A number of studies have looked into whether gestational diabetes is less likely to develop in women who get more exercise from the start of pregnancy than it is in women who don't get much exercise. They found that gestational diabetes was indeed somewhat less common in women who exercised more – regardless of whether they were overweight or had a normal weight.

Studies on women with a normal weight found the following:

• 5 out of 100 women who didn't get much exercise were diagnosed with gestational diabetes, compared to
• 3 out of 100 women who exercised more.

Getting more exercise didn't increase the risk of the baby being born too early (preterm birth). It's not clear whether, or how, higher levels of physical activity affect the risk of complications during birth. It's also not clear whether sports and exercise can help to reduce the need for Cesarean sections. There are contradictory research results here.

Some studies have looked into a combination of dietary changes and exercise programs. This approach was also found to help prevent gestational diabetes.

Doing at least 30 minutes of a strenuous activity on about three to four days per week is sometimes enough to lower blood sugar levels. Suitable types of exercise include swimming, cycling and brisk walking. Sports like martial arts, skiing and soccer are too risky during pregnancy. Women who are at greater risk of preterm birth are usually advised to avoid sports altogether. It's best to talk with your doctor or gynecologist about which types of exercise would be suitable for you.

A number of studies have looked into whether taking metformin has any advantages for very overweight women. Metformin lowers the amount of sugar in your blood. It can be taken in the form of tablets or a solution. But the studies found that metformin didn't prevent gestational diabetes or complications during childbirth. It did cause side effects like diarrhea, though. Because of this, metformin isn't recommended for the prevention of gestational diabetes. It also hasn't been officially approved for the prevention or treatment of gestational diabetes, so it can only be used "off-label" (in a non-approved way).