Diabetes is caused by not having enough of a hormone called insulin. You can think of insulin as a little transporter that takes glucose from the food you eat and carries it to your cells, where it can be converted into energy. If you don't have enough of these transporters, then there is a lot of glucose just hanging out in your blood. That's not good. In Type II Diabetes, the pancreas (which makes insulin) says "Whoa there's a lot of glucose here. I better make more insulin to carry it to where it needs to go." And the pancreas makes more and more insulin until it tires out and just can't do it anymore. At that point you have what's called hyperglycemia - or way too much sugar in your body - and you get sick.
Gestational Diabetes Mellitus (GDM) acts like Type II Diabetes in the way that your body tries to make up for an overabundance of glucose. But it's a little different because what's causing the glucose to build up is not a lack of insulin; instead it's a pregnancy hormone, produced by the placenta, called human placental lactogen (HPL). HPL increases a pregnant woman's cells' resistance to insulin - so when the little insulin transporters come to dock at the cells with their glucose, they are turned away! HPL and the cells' resistance to glucose is a normal development of pregnancy, and peak production of HPL is around 26-28 weeks of pregnancy. In most women, the pancreas is able to keep up with the need for more insulin transporters to take care of all of the glucose, but not always. That's when you get GDM. When you have GDM, your pancreas can't keep up with all of the glucose free-floating around, and the overabundance of sugar can cause problems for both you and your baby.
Most of the time, GDM can be controlled with diet and exercise. This is very important! You can still receive midwifery care and even possibly have a home or birth center birth if you control your GDM! On the other hand, uncontrolled GDM, where glucose levels are running free, can cause a number of problems.
If your blood sugars are high in your first trimester, the result can be heart or nervous system problems for your baby. If early blood sugars are normal, but rise in your third trimester, the risk for genetic problems is not increased, but other risks increase for the baby, including the risk for stillbirth.
Uncontrolled GDM also causes babies to grow bigger than they normally would. Insulin is similar to human growth hormone (HGH), which does exactly what it sounds like it does. As the mother's blood sugar rises, it crosses the placenta to the baby, and the baby's blood sugar rises. Baby doesn't have diabetes, but also reacts by creating more insulin. The increased insulin acts as a growth stimulator for the baby, and he or she gets really big. This is a lifelong change for the child, and has been linked to childhood and adult obesity later in life. A really big baby also can mean problems for the delivery - it can cause stalled labor, shoulder dystocia (where baby's head is born but shoulder gets wedged behind the pubic bone), and the need for Cesarean section.
Complications for mom include high blood pressure, preeclampsia, and the increased risk for developing Type II Diabetes later in life.
So who actually develops GDM? The American Diabetes Association established these guidelines for whether a pregnant woman should get tested for GDM or not. Women that meet all criteria do not need screening:
- Under 25 years old
- Weight normal before pregnancy
- Member of an ethnic group of low prevalence (white American or Western European)
- No known diabetes in first-degree relatives
- No history of abnormal glucose tolerance
- No history of poor obstetric outcome
Most women will not meet every single one of these guidelines. Recommended screening is between 26 and 28 weeks of pregnancy when HPL is at its highest. Currently the medical model of screening is called a Glucose Challenge Test (GCT) or a Glucose Tolerance Test (GTT). You may be asked to fast and then drink a sugary drink, wait an hour (or two), and then your blood is drawn to see how much glucose there is in it.
Another option that is not widely practiced in the obstetric community, but is more common among midwives, is to do home glucose monitoring with finger sticks over a period of time. We do 5 consecutive days of testing, with 4 tests per day. You stick your finger when you wake up before you eat anything, then again 1 hour after each meal (breakfast, lunch and dinner). This gives us a good idea of how your body is metabolizing the foods you are actually eating. With this test, you avoid the sugary drink, which makes a lot of pregnant women nauseous, and you get a good idea of how your body is processing glucose. But you have to be pretty committed to doing the finger sticks over the week at the right times!
Whichever way you choose to go, knowing your risk factors and getting tested for GDM is important. Most pregnant people will test negative for GDM. But if you are one of those who is having high glucose levels, it's important to know this, so that you can make diet and lifestyle changes that allow you to continue with a healthy pregnancy, and hopefully, a home birth!