Glucose screening test results in first and early third trimester of pregnancy: is there any correlation?

This study aims to find correlation between glucose screening test (GST) results done in the first trimester and again in the early third trimester of pregnancy.

Analysis of the records of 458 cases of pregnant women (non-diabetic in early pregnancy as detected by glucose screening test and glucose tolerance test) between 22 and 35 years of age with a body mass index of less than 25 kg/m2 was done. These women underwent GST in the first trimester (GST-1) and again in the early third trimester (GST-2). When the GST-2 was 140 mg% or above, a standard '3 hour glucose tolerance test' was done (GT TEST) with 100 g of glucose. The GST was done by measuring the plasma glucose level 1 hour after taking 50 g of glucose, irrespective of food intake.

A substantial correlation between the two groups of measurements was found. Based on the available data, a GST-1 value of 99 mg% or less was seldom associated with GST-2 value of 140 mg% or more (GT TEST was positive in none). It was observed that 100% of cases with GST-1 value of 140 mg% or more had GST-2 of 140 mg% or more. Out of those having GST-2 value of 140 mg% or more, 72% had GT TEST positive. In the intermediate group (i.e. those patients having GST-1 value of 100 mg%-139 mg%), 51.7% had GST-2 values of 140 mg% or more. Out of these 51.7% cases, only 23% cases turned out to be GT TEST positive. The correlation coefficients (CC) worked out to be 0.38 (substantial correlation for 0.20 < CC < 0.70).

From the observations stated above, it is concluded that for women with GST-1 of 99 mg% or less, a GST-2 is not necessary. For those having GST-1 of 140 mg% or more, a GT TEST is absolutely necessary instead of repeating the screening test again in the third trimester. But it is in the intermediate group (i.e. with GST-1 value of 100 mg%-139 mg%) where the glucose screening test should be repeated in the early third trimester and GT TEST as and when necessary.