ISSN No. 1606-7754                   Vol.11 No.1&2  April-August 2003

The threshold criteria for the 75g oral glucose tolerance test in pregnancy and short-term adverse pregnancy outcomes
C. Savona-Ventura, M. Chircop
Diabetic Pregnancy Joint Clinic, Department of Obstetrics-Gynaecology, St. Luke's Teaching Hospital, Malta.

Abstract

The significant threshold values for the 75g oGTT during pregnancy have yet to be conclusively determined. The study aims to identify the risk significance of a borderline oGTT result. Women undergoing a 75g OGTT during the third trimester of pregnancy were classified into two groups - borderline tolerance (2-h post-load glucose 8.0-8.5 mmol/l: n=75), and GDM (=8.6 mmol/l: n=236). Outcome indicators of these two groups of women were compared to the parameters of the women with a presumed normal carbohydrate metabolism (n = 12185). GDM women showed themselves to be at a significantly increased risk of developing hypertensive disorders during pregnancy and to require obstetric intervention in the form of induction of labour and caesarean section. Their infants were more likely to be macrosomic or preterm and having a low Apgar score at birth. Shoulder dystocia was similarly more likely in infants born to GDM mothers. Women with borderline glucose tolerance did not in any way show any statistically significant increased predisposition to these complications. It would appear the significant threshold for the 75g oGTT during pregnancy should be of the order proposed by the American Diabetes Association criteria where the 2-hour post-load glucose value is = 8.6 mmol/l.

Keywords : Diabetes mellitus, pregnancy, diagnosis, complications

Introduction

The current classification and diagnostic criteria for diabetes mellitus were endorsed by the World Health Organisation in 1980, with modifications in 1985 and 1994.1 Controversy however still exists as to what test is suitable for the diagnosis of gestational diabetes, though the endorsement of the 75g load by the Fourth International Workshop on Gestational Diabetes Mellitus [GDM] in 1997 should have helped break a major stalemate.2 Interpretation of the 75g oral glucose tolerance test during pregnancy remains a contentious issue since the non-pregnant criteria ignore the "diabetogenic" physiological changes of pregnancy. The current American Diabetes Association criteria for GDM require two plasma glucose values = 5.3 mmol/l (fasting) = 10.0 mmol/l (1 hour) and = 8.6 mmol/l (2 hours).3 The 1994 WHO criteria for gestational diabetes still required a plasma glucose = 7.0 mmol/l (fasting) or = 7.8 mmol/l (2 hours).1 The latter diagnostic criteria ignores the physiological changes of pregnancy and thus will include a significant proportion of pregnant women whose carbohydrate metabolism is normal for their pregnant state. The threshold blood glucose levels for the development of complications associated with GDM have yet to be determined. The present study was set up to investigate the risk significance of borderline levels of the 2-hour blood glucose value after a 75-g oGTT performed in the third trimester of pregnancy in a population known to have a high prevalence of carbohydrate metabolism problems, which is reflected in the pregnant population.4

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