What causes gestational diabetes during pregnancy?

Being told you have gestational diabetes can feel worrying, especially if you have always been healthy. Many women ask, “Did I do something wrong?” Usually the answer is no. Gestational diabetes comes from the way pregnancy changes your body’s hormones, meeting the natural limits of your pancreas. Understanding why it happens makes the treatment, and the follow-up after delivery, much easier to accept.

What is gestational diabetes?

Gestational diabetes (GDM) is high blood sugar that is first found during pregnancy. It usually appears in the second half of pregnancy and in most women goes away after delivery.

If very high sugar is found early in pregnancy, it may be diabetes that was already there before pregnancy but not diagnosed. Your doctor will usually check for this after the baby is born.

Why does pregnancy raise blood sugar?

Think of blood sugar as a balance between two things:

• How much insulin your pancreas can make.
• How strongly your body resists insulin.

Every type of diabetes, at its heart, is an imbalance between these two. Pregnancy pushes hard on the resistance side.

As the placenta grows, it releases hormones such as human placental lactogen, placental growth hormone, progesterone, cortisol and prolactin. These hormones make your muscles, liver and fat less sensitive to insulin. By the last three months of pregnancy, the body is roughly half as sensitive to insulin as before pregnancy. The liver also releases more glucose.

This is actually normal and useful. It keeps more glucose and nutrients in your blood for your growing baby.

Why do some women get it and others do not?

In most pregnancies, the pancreas responds by making two to three times more insulin than usual, and blood sugar stays normal.

Gestational diabetes develops when the pancreas cannot increase insulin enough to match the rising resistance. A useful way to think of it is that pregnancy is a stress test for your pancreas. Women who develop GDM often had a smaller reserve of insulin-making beta cells, or some insulin resistance, even before they became pregnant. Pregnancy simply reveals it.

Who is more likely to develop gestational diabetes?

• Being of South Asian, including Indian, origin. Indian women have one of the highest rates of GDM in the world.
• Being overweight before pregnancy, especially with extra fat around the waist.
• A parent, brother or sister with type 2 diabetes.
• PCOS, which is linked with insulin resistance.
• Gestational diabetes in a previous pregnancy.
• A previous baby weighing a lot at birth.
• Being older at the time of pregnancy, generally over 25 to 30.
• Prediabetes or high sugar found before pregnancy.

Many Indian women develop GDM without any of these, which is why testing is recommended for every pregnant woman in India.

When is it tested in India?

Indian government guidelines recommend a glucose drink test for every pregnant woman at the first antenatal visit, and again at 24 to 28 weeks if the first test was normal. The Indian approach uses a single blood sample two hours after the glucose drink, and you do not need to be fasting. Your doctor or lab will explain how the test is done. Indian labs report results in mg/dL; if you are comparing with foreign advice in mmol/L, use the blood sugar unit converter.

What are the effects on mother and baby?

During pregnancy, for the mother: a higher chance of high blood pressure and pre-eclampsia, a large baby and a caesarean delivery.

For the baby: extra glucose crosses the placenta, and the baby makes extra insulin in response. This can lead to:

• A large baby (macrosomia), with a risk of difficult delivery.
• Low blood sugar soon after birth.
• Breathing difficulties and jaundice in some babies.

The good news is that keeping your sugar within target greatly lowers these risks. Most women control GDM with diet and activity changes. Some need medicine such as insulin or metformin; read about metformin in pregnancy.

What does it mean for the future?

For you: gestational diabetes is an early warning sign. Women who have had GDM are about ten times more likely to develop type 2 diabetes later than women who had normal sugars in pregnancy. In India this often happens within a few years. GDM may also come back in a later pregnancy.

For your child: children born after a pregnancy with GDM have a higher chance of obesity and type 2 diabetes as they grow up. A healthy family lifestyle helps protect them too.

What can you do after delivery?

• Have a sugar test 4 to 12 weeks after delivery, as your doctor advises, to make sure the diabetes has gone.
• Then have your sugar checked at least every one to three years for life, as your doctor recommends.
• Breastfeed if you can. It is linked with a lower risk of type 2 diabetes later.
• Aim to return to a healthy weight and stay active. Losing weight and reducing belly fat lowers your diabetes risk. For people who do develop type 2 diabetes, weight loss can sometimes bring it into remission; read can diabetes be reversed.
• Before your next pregnancy, get a sugar test and discuss a plan with your doctor.

What should you ask your doctor?

• What are my sugar targets before and after meals?
• Can I manage with diet changes, or will I need medicine?
• How will we monitor my baby’s growth?
• When and how should I be tested after delivery?

If you have had gestational diabetes, PCOS or a strong family history of diabetes, an endocrinologist can help you plan for a healthy future. Book a consultation.