Gestational Diabetes

About 4% of pregnant women will develop a diabetes-like condition during their pregnancy. Like diabetes mellitis, women with Gestational Diabetes Mellitis (GDM) will have high blood sugars. If not treated, many of these women will give birth to very large babies, a condition known as macrosomia. The baby with macrosomia weighs over 4500 grams, 10 pounds, at birth. A baby this big presents some obvious problems, since the pelvis is designed for something a bit smaller (although most ten-pound babies can fit through the average pelvis).

Even in a healthy, normal pregnancy, there is a noticable change in normal glucose/insulin metabolism. The change is marked by insulin resistance, just like in adult-onset diabetes. This is probably a mechanism by which the fetus receives a preferential glucose supply. In the mother, the process shunts glucose away from muscle and into fat cells for storage and use later. Most of the substances which produce this normal change are produced in the placenta. As the placenta grows larger, more of these substances are produced.

In some women this process is more pronounced, and their blood sugar levels approach those seen in woman with diabetes. When blood tests show that these sugar levels are becoming dangerously elevated, measures are taken to lower them, and the woman is classified as GDM.

It is now recommended that all pregnant women be screened for GDM. The usual screening test, the 1-hour Glucose Tolerance Test (GTT), is given between 24 and 28 weeks gestation. The woman is given a measured amount of sugar (in the form of a drink), and the blood glucose is measured one hour later. If the level is greater than 140, it is recommended that she receive a longer version of the test, a three-hour GTT. During the 3-hour GTT, blood is drawn in the fasting state (so, no breakfast on the morning of the test!), and then at 1 hour, 2 hours, and 3 hours after drinking the sugar drink. If 2 of the values are elevated, GDM is diagnosed. It is particularly bothersome if the Fasting Blood Sugar is elevated.

Most women with GDM are managed by alterations in nutrition and monitoring of their blood sugars. Most will not need insulin. The newly diagnosed GDM woman should be seen by a nutritionist or RN who specializes in diabetic teaching. There are some recommended calorie-intake limits, but it is generally recognized that a 300-400 calorie increase (over a healthy prepregnant intake) is necessary for the demands of the pregnancy. Since blood sugar levels are most sensitive to carbohydrates, it is recommended that the percentage of calories consumed as carbohydrates be restricted to 40-50%. 40% of calories should come from fats (and only one third of those should be saturated fats). The remaining calories, 10-20% of the total, should come from proteins. Total daily calorie intake should be about:

  • 30 Calories/kg for women of normal body weight
  • 24 Calories/kg for overweight women
  • 40 Calories/kg for underweight women (a kilogram[kg] is 2.2 pounds)

It is generally recommended that a woman with GDM, controlled by diet alone, try to gain no more than 15 pounds. Weight limits in pregnancy are difficult to manage…..for both the pregnant woman, and her clinician. What is most important for the woman with GDM is control of her blood sugars.

A nutritionist/dietician, or a RN diabetic specialist, will help you construct a specific menu tailored to your eating habits. But in many cases, a woman’s eating habits are one of the predisposing factors in diabetes. In order to keep your blood sugars within normal limits, you may have to dramatically alter the foods you eat. You will probably be instructed in some method of home-blood-sugar-monitoring. This means you will learn to stick a finger for a drop of blood in order to measure your blood sugar level. Over the course of a week or so, you will notice that some foods (usually carbohydrates) raise your blood sugars more quickly and more markedly than other foods……..these are generally the foods to avoid.

You will probably be instructed to perform finger sticks before you eat in the morning, and then one or two hours after a meal. There are now fairly inexpensive, electronic blood sugar monitors that you may purchase, rent or borrow. In any case, the cost of these monitors is cheap compared to even a minor complication of uncontrolled diabetes in pregnancy. If you are unable to acquire an electronic blood sugar monitor, you may use a dipstick-type method which uses a color-comparison bar to gauge the blood sugar level.

It is extremely important that your Fasting Blood Sugars (FBS), those measured after 12 hours of no food (that’s why you do them in the morning), stay within normal limits. If your FBS is consistently above 105, you may need to use some insulin to avoid problems with your pregnancy.

Your post-prandial sugars, those measured one or two hours after a meal, should also remain below a certain level. Currently, the use of the 2-hour post-prandial seems most popular, and it should be below 140. You should keep a log of all your blood sugar measurements, and take them with you when you see your doctor or midwife.

If you are able to keep your blood sugar levels in good control (FBS < 100: 2-hour post-prandials < 140) with diet alone, your doctor or midwife will otherwise manage your pregnancy as though you did not have GDM.......with a few exceptions. If you have not had your baby by the due date (40 weeks), you should begin twice-weekly fetal testing. These tests for fetal well-being utilize both an electronic fetal monitor (EFM) to evaluate fetal heart rate patterns, and ultrasound, to evaluate the placenta, amniotic fluid volume and fetal movements. If your clinician suspects that your baby is getting too big, or you begin to go more than one week beyond your due date, labor may need to be induced. Estimating the weight of a fetus is quite difficult. Although there are now programs in ultrasound machines that will estimate the weight based on fetal body measurements, the estimates are often inaccurate. Studies have tried to determine what is the most accurate way to estimate fetal weights. These studies show that almost all estimates are unreliable and often inaccurate. A future generation of ultrasound machines will have 3-dimensional imaging.....these machines promise to bring improved accuracy to the estimation of fetal weights......but we'll have to wait for a new century for them. The significance of this problem cannot be emphasized enough......If you have a problem with diabetes before or during your pregnancy, please do not take this problem lightly. A comparison of the outcomes between diabetic and non-diabetic pregnancies is all too convincing of the importance of good blood sugar control BEFORE and DURING your pregnancy.