Medically, Gestational (jes-TAY-shun-ul) Diabetes Mellitus (GDM) is defined as glucose intolerance, which is diagnosed during pregnancy. It is reported to affect approximately 7% of all pregnancies. GDM can adversely affect both the mother and the baby; hence a diagnosis, if made, should be taken seriously.
Gestational (jes-TAY-shun-ul) Diabetes Mellitus (GDM) is a form of diabetes that affects approximately 4% of pregnant women. In India an overall prevalence of 9 to 18% has been reported. GDM can adversely affect both the mother and the baby; hence a diagnosis, if made, should be taken seriously.
The risk factors for GDM include – A family history of diabetes, obesity or testing positive for glucose in the urine. Most pregnant women will undergo screening to check the blood glucose level. If the readings are high, they will be advised to undergo an Oral Glucose Tolerance Test. Blood samples are taken while fasting and also during one, 2 and 3 hours after having 100 gms of glucose. These samples are tested in the laboratory and the readings are interpreted.
Sample drawn after 100-gram glucose drink (glucose load)
Time of Sample Collection
Fasting* (prior to glucose load)
95 mg/dL (5.3 mmol/L)
1 hour after glucose load
180 mg/dL (10.0 mmol/L)
2 hours after glucose load
155 mg/dL (8.6 mmol/L)
3 hours after glucose load*
140 mg/dL (7.8 mmol/L)
INDICATION: If two or more values meet or exceed the target level, gestational diabetes is diagnosed.
Reported prevalence of GDM in a region depends on the methods and criteria used to establish its diagnosis. For example - WHO uses 75 grams of oral glucose load and not 100 gms as described above. It also suggests only two samples of blood – one while fasting and the other at 2 hours after consuming glucose. This method is more cost effective and is used frequently in India.
The National Institutes of Health Diabetes Data Group (NDDG) from the USA (Diabetes 1979;28:1039) and the values established by Carpenter and Coustan (Am J Obstet Gynecol 1982;144:768-73) uses a 100 gram glucose load. Their diagnosis is based on four measurements (fasting, 1, 2 and 3 hr. glucose levels).
Over the years different investigators have come up with different values with small variations as shown in the chart below.
Carpenter & Coustan (1982)
Sacks et al (1989)
Remember that women diagnosed with GDM can develop diabetes later on in their life. Hence they are advised to undergo annual screening to enable early diagnosis or to rule out the condition.