April 25, 2014
Gestational diabetes (GD) was previously considered the onset of diabetes during pregnancy in patients that have never been diagnosed before the pregnancy. This meant that women tested at any time (first, second, or third trimester) were diagnosed as having GD. However, in the past few years, the American Diabetes Association (ADA) changed the GD definition to only include women diagnosed during their 24th to 28th week of pregnancy.
Therefore, high-risk women should be screened for overt diabetes during their first pre-natal medical visit (presumably in their first trimester). Overt diabetes utilizes the standard fasting and post-prandial glucose levels used for non-pregnant women. Some risk factors for developing GD include:
- Older than 25
- Family history of diabetes
- Previous delivery of a baby weighing more than 9 pounds or had a birth defect
- Genetic factors
- Ethnicity – Mexican-Americans and African-Americans
- Overweight before pregnancy
For women who are not diagnosed with overt diabetes, a follow-up screening for GD should be done at 24 to 28 weeks of gestation. In 2014, the GD diagnostic criteria was updated to provide 2 options for screening patients. The ADA recommends using either a “one-step” or “two-step” oral glucose tolerance test (OGTT). Descriptions of the tests are as follows:
- One-step: perform a two-hour, 75 grams OGTT after fasting for 8 hours. GD is diagnosed when any of the following plasma glucose levels are exceeded:
- Fasting ³ 92 mg/dL
- 1-hour post test ³ 180 mg/dL
- 2-hour post test ³ 153 mg/dL
- Two-step: start with a one-hour 50 grams OGTT (non-fasting). If the plasma glucose level exceeds the following, continue with step two.
- Step one:
- 1-hour post 50 g OGTT ³ 140 mg/dL, proceed to step two using the 100 gram OGTT
- Step one:
- Step two:
- 3-hours post 100 g OGTT ³ 140 mg/dL indicates GD
The benefit of the two-step method is that fasting is not required and therefore may be easier and more convenient for more women to get the test done. It is also a better method to identify GD sooner, resulting in earlier interventions and reduced complications for mother and baby.
Untreated or uncontrolled GD can lead to an increased risk of macrosomia (head to body disproportion) and a large birth weight due to the increased maternal glucose delivery in the third trimester. The larger weight baby is more likely to have a birthing injury (i.e. broken bones) than a normal sized infant. There is also an increased risk of malformations in children born from a mother with uncontrolled diabetes, especially with overt diabetes. The baby is also more likely to experience hypoglycemic events post-delivery due to the increase insulin release of the pancreas, without the glucose delivery from the mother anymore.
Typically, the mother’s blood glucose levels will return to normal post-partum. However, women should be screened for persistent diabetes 6-12 weeks postpartum using the OGTT. It is important to note that the A1c is not used to diagnose GD or overt diabetes in the postpartum stage, due to the more “acute” glucose changes in this population.
Finally, women who have a history of GD should have lifelong screening for type 2 diabetes (T2D). Screening for pre-diabetes or diabetes is recommended at least every 3 years. This is because many women develop T2D within 5-10 years after delivery. If a patient is found to have pre-diabetes, the ADA recommends starting lifestyle modifications and metformin to prevent the development of diabetes.
Susan Cornell, PharmD, CDE, FAPhA, FAADE, is an associate professor of pharmacy practice and assistant director of experiential education at the Midwestern University Chicago College of Pharmacy. She is also a clinical pharmacist/certified diabetes educator with Dupage Community Clinic in Wheaton, IL.
Daniel Morrow, 2014 PharmD Candidate, co-authored this post.
1. American Diabetes Association. Standards of medical care in diabetes 2014. Diabetes Care. 2014;37(supp 1):S14-S80.
2. Metzger BE, Lowe LP, Dyer AR, et al.; HAPO Study Cooperative Research Group. Hyperglycemia and adverse pregnancy outcomes. N. Engl J Med. 2008;358(19):1991-2002.
3. Metzger BE. Gabbe SG, Persson B, et al.; International Association of Diabetes and Pregnancy Study Groups Consensus Panel. International Association of Diabetes and Pregnancy Study Groups recommendations on the diagnosis and classification of hyperglycemia in pregnancy. Diabetes Care. 2010;33(3):676-682.
4. Vandorsten JP, Dodson WC, Espeland MA, et al. NIH consensus development conference: diagnosing gestational diabetes mellitus. NIH Consens State Sci Statements. 2013;29(1):1-31.
The views expressed on this blog are solely those of the author and do not necessarily reflect the views of Pharmacy Learning Network or other Pharmacy Learning Network authors. Blog entries are not medical advice.