In order to understand gestational diabetes, it is necessary to understand how insulin works. The hormone insulin which comes from the pancreas controls blood sugar. The role of insulin is to get the sugar into the cells. If for any reason the insulin is not working properly or there is not enough of it, the blood sugar will rise and if it rises high enough we call it diabetes.
The difference between diabetes and gestational diabetes is that diabetes simply means your blood sugar is too high whereas gestational diabetes is any diabetes that arises or is first identified during pregnancy.
During pregnancy the afterbirth or placenta releases hormones that circulate through your body. These hormones block how the insulin works and thus raise the blood sugar the purpose being to provide energy for the baby. Therefore, even in a normal pregnancy the pancreas has to make a lot of extra insulin just to keep the situation controlled. When the pancreas is not making enough insulin to overcome the blockage from these hormones, the blood sugar will rise, and this is called gestational diabetes.
What causes it?
The main problem is a mother’s pancreas not able to make enough insulin. There is a resistance to the insulin being made caused by the placental hormones but a normal pancreas can usually make enough insulin to overcome this insulin resistance. If the pancreas does not make the extra insulin, the sugar will rise and gestational diabetes occurs.
What are the risk factors?
The mothers weight can be a factor. If cells are swollen with fat owing to weight problems prior to pregnancy or if during the pregnancy excess weight is gained, it is more difficult for the insulin to get sugar into the cells. You are expected to gain weight in pregnancy, just not too much. Some ethnic groups are more prone to gestational diabetes for instance Hispanic, Native Americans, South East Asians among others. A history of having delivered a big baby is also a clue of potential gestational diabetes. Age over 25 makes a difference, the older the mother the less well her pancreas works. A family history of Type 2 diabetes is often another clue to the mother’s pancreas having a problem.
What are the symptoms?
Gestational diabetes is usually a mild form of diabetes, so that you will rarely feel any symptoms of high blood sugar. Many pregnant women have to pass urine frequently, get up at night to pass urine and have tiredness. These are also symptoms of diabetes but usually occur when the sugar is much higher than what is typically seen in gestational diabetes. Thus the symptoms most women have with gestational diabetes are those of the pregnancy and not the gestational diabetes.
What harm can it do to the baby?
Unfortunately, the high sugar in the mother is transferred to the baby. It is not good for the baby to be exposed to high blood sugar. It is as if the baby converts the high sugar into fat. Therefore, these babies tend to be bigger, making the delivery more difficult for both the mother and the infant. There are other causes of big babies and sugar is only one of the reasons a baby may be large.
If a baby is exposed to high sugars during pregnancy, once they are born and the mother is not supplying extra sugar, the sugar in the newborn can become too low. High sugar during pregnancy also causes these bigger babies to be less mature for their actual weeks gestational age. They may act like premature babies and are at risk of developing jaundice and other problems.
Finally, if the gestational diabetes is totally uncontrolled there is a minimally increased risk of a stillbirth but large studies have shown that the risk of stillbirth is actually lower in women with treated gestational diabetes.
There is some evidence that if the mom has gestational diabetes the children in the long term may be at increased risk of obesity and glucose intolerance but sorting out the role of the mother’s obesity and/or genes in this situation is very difficult.
The baby will not be born with diabetes in the typical case of gestational diabetes.
What harm can it do to the mother?
In the short term the problems relate to delivering a baby that is large. There is also a slightly increased risk of pre-eclampsia – a condition of high blood pressure and protein spilling into the urine. The diabetes nearly always goes away after the baby is born. However, the mother’s pancreas is now known to have some problems coping with situations where extra insulin is needed. Thus, though there is an increased risk for the mother in the long term for developing diabetes. Controlling the mother’s weight in the long term, with diet and exercise, can diminish this risk.
How to screen for it?
Because gestational diabetes typically has no symptoms most diabetes organizations suggest that all pregnant women not know to have diabetes be screened for gestational diabetes. Some countries suggest only checking those at higher risk (overweight, family history of Type 2 diabetes, member of an ethnic group predisposed to gestational diabetes, older age, history of delivering large babies). Other countries suggest that every pregnant woman who does not have diabetes be checked. Because it is the hormones from the placenta causing the insulin resistance that tips the balance, usually gestational diabetes is checked for between 24 to 28 weeks of gestation when it is most likely found. If diagnosed earlier it usually means the pancreas is not coping when there is not much insulin resistance, raising the possibility of Type 2 diabetes being present pre pregnancy or persisting after delivery.
Checking someone for gestational diabetes is a common procedure in that the pregnant woman is given a 50 gram glucose drink at any time of the day. An hour later a blood test is taken and if the blood sugar is less than 7.8 mmol/l (140 mgs%) then it is most likely gestational diabetes is not present. If the blood sugar is 7.8 mmol/l (140mgs%) or higher then gestational diabetes may be present. In several countries the practice is just to go straight to a 75 gram oral glucose tolerance test. This has the advantage that it is just one test, the disadvantage that a single abnormal value that may be just a little high leads to a diagnosis of gestational diabetes.
How to diagnose it? If the 50 gram gestational diabetes screen test is over the limit then a full oral glucose tolerance test is needed. In some situations if the blood sugar on the 50 gram screen is very high then the likelihood of the oral glucose tolerance test being abnormal is so high that it can be presumed gestational diabetes is present and treatment for gestational diabetes can be started. In Canada a level of 11.1 mmol/l (200 mgs%) at the one hour time mark is used to presume gestational diabetes is present.
For the oral glucose tolerance test most countries use a 75 gram glucose drink test. The blood sugar is usually checked before the start and at the one and two hour time mark. Different countries set different cut offs for normal and some require either one or two of the three values to be over the cut offs to make a diagnosis of gestational diabetes. In Canada the currently preferred cut offs are that the fasting level should be under 5.3 mmol/l (95 mg%), the one hour level should be under 10.6 (191 mgs%) and by two hours the blood sugar should be under 9.0 mmol/l (165 mg%). As mentioned some use just a single oral glucose tolerance test and prefer to use lower cut offs: a fasting level should under 5.1 mmol/l (92 mg%), the one hour level should be under 10.0 (180 mgs%) and by two hours the blood sugar should be under 8.5 mmol/l (153 mg%) and if one of these values is high then a diagnosis of gestational diabetes is made.