The validity of oral glucose tolerance test after 36 weeks' gestation.

OBJECTIVE

Secretion of anti-insulin hormones plateaus near term, questioning the validity of OGTT (oral glucose tolerance test) during that period. We aimed at assessing the feasibility of OGTT near term as compared to OGTT at 26-32 weeks.

PATIENTS AND METHODS

One thousand four hundred and eighty seven pregnant women were screened by GCT (glucose challenge test), and 282 (19%) of them performed an OGTT at 26th-32nd weeks ("early" OGTT) after meeting the threshold value for GCT. Forty-one women with abnormal and 16 with normal early OGTT underwent a repeated OGTT at 36-40 weeks' gestation ("late" OGTT). Blood glucose levels during GCT and OGTT were compared between women with early and late abnormal OGTT and women who converted from early abnormal to late normal OGTT.

RESULTS

Thirty-six out of 41 participants (88%) with early abnormal OGTT had abnormal test near term as well (Group I). Five women with an early abnormal OGTT converted to normal according to a late OGTT (Group II). These women had lower glucose levels on both late and early OGTT as compared with Group I. All 16 women who tested normal on early OGTT had a consistently normal late OGTT. Glucose levels for all 57 women did not significantly differ between early and late OGTT. The sensitivity, specificity, and positive and negative predictive values of late OGTT were 88%, 100%, 100%, and 76%, respectively.

CONCLUSION

The positive predictive value of late OGTT performed at 36-40 weeks' gestation is 100%. This test may be used to detect gestational diabetes in women near term.