Screening for Diabetes During Pregnancy

Gestational diabetes [GDM] is usually diagnosed around 24 to 28 weeks of pregnancy. Most (94%) obstetricians perform a screening test at that time which involves drinking a sweet drink (glucola) which contains 50 grams of glucose and checking blood sugar levels one hour later.

For those who have trouble drinking the sweet drink, consuming 18 "Brach & Brock" jelly beans has been shown to be just as effective for screening as the glucola drink. Some advocate screening only patients with risk factors for diabetes, however this would miss approximately half of the women with GDM.2

There are some women who are at particularly high risk for developing GDM and who should be screened early in pregnancy and again at 24 to 28 weeks if the first test was negative. Early screening should be considered particularly in those who are obese, have a history of prior glucose intolerance or GDM or have a family history of diabetes.

SCREENING PROTOCOL FOR GDM 

Abnormal 3 hour OGTT if >= 2 values of the 4 meet or exceed limits below (Carpenter and Coustan)2 **

Fasting 2 >= 95 mg/Dl
One hour >= 180 "
Two hours >= 155 "
Three hours >= 140 "

If despite diet therapy, fasting blood sugars are > 95 mg/dl and/or the 1-2 hour
post-prandial blood sugars are > 120 mg/dl, insulin treatment will most likely be required.

* Some obstetricians use 130 or 135 mg/dl as the cutoff for proceeding with a 3 hour OGTT.2 If the 1 hour test is > 190 mg/dl, there is no need for a 3 hour OGTT because more than 90% of the time, the 3 hour test will be abnormal. A fasting and 1 hour post-prandial blood sugar should be checked instead, in order to see if insulin is required immediately or whether blood sugars can be controlled with a diet.

** ADA Clinical Practice Recommendations & 4th International Workshop on GDM 1998

Goals for blood glucose control before and during pregnancy

Time of Day

Blood Sugar (mg/dl)

Fasting 60-90
Before Meals <=95
1-hour after meals <120
0200-0300AM 60-120

 

References:
Boyd KL et al. Jelly beans as an alternative to a cola beverage containing fifty grams of glucose. Am J Obstet Gynecol 173(6);1889-1892, 1995.
ACOG Practice Bulletin. Gestational Diabetes. Number 30, Obstetrics and Gynecology, Vol. 98 (No.3):525-538, 2001