Important: This is intended as general information only. It may not apply to your specific situation. It is not a substitute for medical advice. If you have a question or concern, please raise it with me at your next appointment or contact me sooner if it's urgent.
What is gestational diabetes?
Gestational diabetes (GDM) is a form of diabetes that occurs in pregnancy. In all but a few cases, it resolves after delivery. Between 4 and 8% of pregnant women are diagnosed with GDM and the disease usually develops between 24 and 28 weeks gestation.
As you may be aware, there are a few different forms of diabetes. Type I diabetes is an autoimmune disease in which the immune system destroys the cells in the pancreas that produce the hormone insulin. This leaves the type I diabetic without insulin and dependent on several injections of insulin per day to remain healthy. This disease is quite different from GDM and we won’t be talking about it any further here.
Type II diabetes is a disease in which the pancreas continues to produce insulin but the body becomes less sensitive to it’s effects. This is called insulin resistance. Put another way, there is still insulin present but it doesn’t work as well. This is similar to what happens in GDM and, in fact, we know that people with GDM are at risk of developing type II diabetes later in life. Insulin resistance may be genetic or as a result of various lifestyle factors such as obesity and a sedentary lifestyle. Insulin resistance is also seen in polycystic ovarian syndrome.
Insulin is required to keep our blood sugar levels stable. Normally, blood sugar is kept within a narrow range. It can be dangerous to have blood sugar that is too high or too low. In diabetes, we commonly see high blood sugar levels although sometimes the medications used to treat diabetes can result in low blood sugar levels.
What causes GDM?
Pregnancy makes everyone a little bit insulin resistant due to some of the hormones produced by the placenta. This may result in slightly higher than usual (although still normal) blood sugar levels. This is thought to be beneficial to the baby as it makes sure there is plenty of sugar available for your growing baby.
For women who already have some underlying insulin resistance (which may be genetic or due to their weight), the extra insulin resistance of pregnancy may be enough to make them diabetic.
Who gets GDM?
Women who are at risk of gestational diabetes include:
- Women previously diagnosed with PCOS
- Women with a family history of type II diabetes
- Women who have had GDM in a previous pregnancy
- Women who have previously had large babies
- Some ethnic groups
- Overweight or obese women
- Women over the age of 30
However, some of the women diagnosed with GDM don’t have any of these risk factors. GDM doesn’t usually cause much in the way of symptoms so in order to diagnose it, we test everyone for GDM between 24 and 28 weeks gestation. Women at very high risk, or women who have had GDM before may be tested at an earlier gestation.
What is the problem with GDM?
Sugar crosses the placenta freely so if the mother’s blood sugar level is high, the baby’s will be too. This can result in the baby growing bigger and fatter than it was meant to, which is called macrosomia. As you might imagine, the bigger the baby, the harder it is to get out. This can result in an increased need for delivery by caesarean section and, in the case of vaginal delivery, increased trauma to the mother and the baby.
While the mother provides the sugar, the baby makes its own insulin. If the baby is exposed to high sugar levels from his or her mother, he or she will produce extra insulin. After delivery, the baby is cut off from it’s source of sugar, but it can take some time for his or her insulin levels to readjust. This means that, initially, the baby may have high insulin levels without high glucose levels. This can cause hypoglycaemia (episodes of low blood sugar) which can be dangerous.
In addition, a very high sugar environment seems to be dangerous for babies in utero. In poorly controlled diabetes, we see an increased number of pregnancy complications such as miscarriage, preterm birth and stillbirth.
The good news is, by carefully controlling blood sugar levels in women with GDM (more about this later), we can avoid these complications.
Women who are diagnosed with GDM are given an important ‘heads up’ that they are at increased risk of type II DM later in life. Of course, nobody wants to hear that they are at increased risk for any disease but, as they say, forewarned is forearmed. If you know that you have this tendency lurking in your genes, you can take steps to minimize its impact on your life. Mostly, this involves the usual healthy lifestyle things we all should be doing like eating well, exercising regularly and maintaining a healthy body weight. It also means seeing your GP regularly for health checks so that if you do develop diabetes it is diagnosed early and managed well.
How to treat GDM
If you are diagnosed with GDM, I will refer you to an endocrinologist and a diabetes educator and we will manage you as a team. The first thing we will do is teach you to monitor your blood sugar levels before and after meals to get a feel for what your sugar levels are like throughout the day. You usually have to modify your diet and undertake a sensible amount of regular exercise. We will give you plenty of advice on how to do this safely in pregnancy. For many women, no further management is needed. For some women, however, diet and exercise will not result in normal sugar levels and these women require treatment with insulin injections.
Due to the risk of macrosomia, all women with GDM will have a third trimester ultrasound scan to assess the baby’s growth (even if their blood sugar control has been good). Because of the association of GDM with some pregnancy complications, there will also be increased monitoring of the baby.
Having GDM may influence when your baby is born. For women who have well controlled blood sugar levels without needing insulin, we usually deliver them around their due date if they have not laboured beforehand. For women requiring insulin or in whom control has not been ideal, we usually recommend delivery around 38 weeks. Unless your baby is known to be very big, there is no reason why you can’t try to have a vaginal delivery.
After delivery, we monitor the baby’s blood sugar until we are sure that it is stable. It’s usually not necessary to monitor the mother’s blood sugar after delivery as we are expecting that the GDM will resolve over a couple of weeks as the pregnancy hormones disappear. However, we always do a diabetes test about 6 weeks after delivery to make sure that everything has returned to normal.