Gestational Diabetes Mellitus
From Ask Dr Wiki
By Nadia Ali M.D, M.B.B.S.
Gestational Diabetes Mellitus is defined as glucose intolerance diagnosed during pregnancy. This could either be newly diagnosed type 1 or type 2 Diabetes Mellitus or this could be a new onset of hyperglycemia secondary to metabolic changes related to pregnancy.
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Screening
It is recommended that pregnant women with any risk factors be screened at the first prenatal visit. The risk factors are
- age ≥ 25 years
- Obesity
- Previous history of GDM
- History of large for gestational age infant
- Family history of diabetes
- History of polycystic ovary disease
- Glycosuria
- Member of ethnic group with low diabetes prevalence.
- History of poor obstetric outcome.
- History of prior glucose intolerance
For women at high risk not found to have GDM at the first visit, repeat testing is indicated between 24 and 28 weeks.
Diagnosis
There are two approaches to diagnosing GDM. One can either take a two step approach, starting with the 50 gm glucose challenge test, followed by an oral glucose tolerance test if the results of the former test are abnormal. The other way is to directly do a 3 step 100 gm oral glucose tolerance test.
If 2 or more values are abnormal then the patient has a positive diagnosis of gestational diabetes.
Pathophysiology
Pregnancy is a state of relative insulin insensitivity. During the early part of pregnancy there is increase in insulin secretion and beta cell hyperplasia. This leads to an increase in insulin sensitivity with low fasting blood sugar levels, increased glucose uptake by peripheral tissue and glycogen storage as well as decreased hepatic gluconeogenesis. This process is crucial for the build-up of maternal adipose tissue, to be used in the later part of pregnancy. During the late phase, there is an increase in hormones such as cortisol, prolactin, progesterone and human placental lactogen which leads to a state of relative insulin resistance, possibly via a post receptor defect in the cells. This is a critical step which ensures adequate delivery of nutrients to the fetus. The pancreas respond to this increased resistance by doubling the release of insulin.
It has been found that women diagnosed with gestational diabetes already have insulin resistance at baseline with a higher level of plasma insulin levels. This state gets further aggravated by the metabolic changes associated with pregnancy. The pancreas however, is unable to cope with this additional stress of elevated level of insulin resistance. This results in an inadequate release of insulin and elevated blood sugar levels.
Management
Women diagnosed with GDM need training about daily self monitoring of glucose 6-7 times a day with a minimum of 4 times. The target pre-meal blood sugar is <95mg/dl, 1 hour post meal <140mg/dl and 2 hour post meal <120mg/dl. Testing for the presence of ketones in a fasting urine sample is a valuable tool to assess the adequacy of caloric intake in these patients. Positive urine for ketones indicates a state of starvation and the patients should be advised to increase their daily caloric consumption.
Modalities for treating GDM
Diet and Exercise
All women diagnosed with GDM require nutritional counseling for the appropriate amount of weight gain during pregnancy as well as dietary control. Women with a normal BMI [20-25], can consume about 30kcal/kg/d while those who are obese [BMI >25-34] should restrict their diet to 25 kcal/kg/d and those that have a BMI >34 should consume 20kcal/kg/d or less. These patients should restrict fat intake and substitute simple or refined sugars in their diet to more complex carbohydrates. Moderate amount of non-weight bearing exercise is an important adjunct to dietary advice. It is recommended that pregnant women exercise for about 20-30 minutes everyday or at least most days of the week. It is a critical point in time for changing the lifestyles of these women since they are at a high risk for development of type 2 diabetes.
Insulin therapy
Insulin therapy in patients with GDM is based on pre-pregnancy BMI. Women who are lean before conception, the insulin dose requirement is 0.8U/Kg and for the obese women it is 0.9-1U/kg. There is insufficient evidence available regarding the safety of the insulin analogues, Aspart and Lispro hence regular human insulin is the treatment of choice and can be combined with intermediate or basal insulin such as NPH/ lente/ ultralente. There isn’t enough data regarding the safety of the long acting insulin glargine in pregnancy.
Oral Hypoglycemics
The use of oral medications is considered when diet and exercise do not adequately control blood sugars. Some studies have recently evaluated the safety and efficacy of Glyburide [sulphonylurea] after the first trimester for treatment of GDM. The older sulphonylureas were not recommended for use in pregnancy because they crossed the placenta. Glyburide only minimally crosses the placenta. It has been shown that it is as effective as insulin, more cost effective than insulin and safe for use in pregnancy. Both American Diabetic Association [ADA] and American college of Obstetricians and Gynecologists [ACOG] await more research related to the effect of glyburide on maternal and perinatal outcomes before approving its use. There is inadequate data in regards to the safety and efficacy of other oral antidiabetic medications such as Metformin, thiazolidinediones and Acarbose.
Complications
The diagnosis and treatment of gestational diabetes is critical because elevated blood sugars adversely affect both the mother and the baby. The fetus is at increased risk of macrosomia, hypoglycemia, hypocalcemia, hypomagnesaemia, jaundice, polycythemia, respiratory complications, congenital malformations and fetal loss including abortion, still births and neonatal deaths. The risk of congenital anomalies is related to the degree of glucose control during organogenesis (i.e., the first 6–8 wk gestation). Women with normal pregravid glucose tolerance who develop gestational diabetes in late gestation have no increased risk of fetal congenital anomalies beyond the population risk for women with normal glucose metabolism. Fetal macrosomia leads to increased susceptibility to shoulder dystocia and birth trauma. Women diagnosed with gestational diabetes are at increased risk of gestational hypertension including preecclempsia, caesarian section and assisted deliveries.
Postnatal Care
Approximately 50% women will develop type 2 diabetes within 5 years of development of gestational diabetes. The greatest risk factor for early-onset type 2 diabetes after pregnancy was early gestational age at the time of diagnosis and elevated fasting glucose. The greatest long term risk factor was maternal obesity. Hence these women should be screened by a 75 gm 2 hour oral glucose tolerance test. The children of women diagnosed with GDM are at increased risk of obesity and abnormal glucose metabolism during childhood, adolescence and adulthood. One of the mechanisms thought to be contributing to the long term complications in these babies is ‘early onset hyperinsulinimia’. Hence these children need close follow up.
