Influence of Pregnancy on the 75-g OGTT: A Prospective Multicenter Study

Abstract

This study reports the responses to a 75-g oral glucose tolerance test (OGTT) in 1009 pregnant women from throughout Europe. We reached the following conclusions. 1) A pregnant woman tends to have blood glucose concentrations that are elevated for a longer period of time after an oral glucose load. Therefore, ∼ 10% of women will reach or exceed 8 mM glucose at 2 h, but it is unlikely that 10% of European women have disordered carbohydrate metabolism. 2) The fasting and 1-h values should be included in any analysis of the response of the patient. By doing this, many fewer women will have responses regarded as abnormal; in this series, it reduced the 79 women with a 2-h value >8 mM to 15 who were considered to have carbohydrate intolerance (2 with diabetes, 13 with impaired glucose tolerance [IGT]). 3) By increasing the 2-h cutoff value to >9 mM, the number of women regarded as at risk would be reduced by >50% (from 79 to 32 in this series), but 10 of the 13 women with two abnormal values would still have been detected, as would the 2 diabetic women. 4) From the obstetric viewpoint, mothers who screen positive do not have bigger babies, they deliver close to term, and they do not have particular stigmas such as a family history of diabetes or an increased tendency to smoke or to have an adverse obstetric outcome. However, they do tend to be older and heavier. This raises the question of whether the apparent longer-term consequences such as coronary artery disease and hypertension are not in some measure due to these factors rather than carbohydrate intolerance alone. 5) We recommend that the screening test for disordered carbohydrate tolerance should be based on a 75-g OGTT with at least three blood samples: fasting, 60 min, and 120 min. The fasting value should not exceed 7 mM, the 1-h level should be <11 mM, and the 2-h value should be <9 mM. To diagnose IGT, either the fasting or 1-h concentration should be above the stated values in addition to a 2-h value >9 mM. Diabetes should be diagnosed with the existing World Health Organization criteria. 6) The term gestational diabetes should be reserved for those in whom blood glucose levels are diagnostic of diabetes and not IGT. If the term IGT during pregnancy is too long, the abbreviation gestational IGT is a reasonable alternative.