Pregnant women with gestational impaired glucose tolerance (GIGT) may exhibit the same adverse outcomes as do women with gestational diabetes mellitus, according to the results of a new study
Diabetes is a common complication of pregnancy, and most women receive testing with an OGTT during the second trimester. Women with a positive result on screening examination usually receive a 3-hour OGTT to identify gestational diabetes mellitus. Although glucose levels at baseline and during each hour of this testing are used in making the diagnosis, it appears that the 1-hour OGTT results are particularly linked with risk factors for diabetes mellitus. Previous research has demonstrated that impaired glucose tolerance at 1 hour is associated with higher insulin resistance and worse pancreatic β–cell function vs impaired glucose tolerance at hours 2 and 3 of the 3-hour OGTT.
The current study examines how 1-hour glucose levels can affect metabolic as well as birth outcomes.
"GIGT, defined by a single abnormal value on antepartum 3-h oral glucose tolerance test (OGTT), is a metabolically heterogeneous disorder," write Ravi Retnakaran, MD, from the Leadership Sinai Centre for Diabetes, Mount Sinai Hospital in Toronto, Canada, and colleagues. "Indeed, the antepartum metabolic phenotype of women with a single abnormal value at 1 h during the OGTT (1-h GIGT) resembles that of women with gestational diabetes mellitus (GDM), whereas GIGT at 2 or 3 h (2/3-h GIGT) is similar to normal glucose tolerance (NGT). Thus, we hypothesized that 1-h GIGT would be associated with the same adverse outcomes as GDM, i.e., increased infant birth weight and postpartum metabolic dysfunction."
In this study, 361 women underwent an antepartum glucose challenge test (GCT) and a 3-hour OGTT. Obstetric outcome was evaluated at delivery, and OGTT was performed at 3 months postpartum. On the basis of antepartum GCT/OGTT, participants were categorized into 5 study groups: gestational diabetes mellitus (n = 97), 1-hour GIGT (n = 28), 2/3-hour GIGT (n = 34), abnormal GCT NGT (abnormal GCT result with NGT on OGTT; n = 128), and normal GCT NGT (normal GCT result with NGT on OGTT; n = 74). Glycemia was defined as an area under the glucose curve, and β-cell function was measured with an insulinogenic index/homeostasis model determination of insulin resistance.
Although the rate of cesarean delivery was higher in women with 1-hour GIGT, birth weight was not significantly different between the groups without gestational diabetes mellitus (P = .1978). Glycemia at 3 months postpartum progressively increased across the groups from normal GCT NGT to abnormal GCT NGT results to 2/3-hour GIGT to 1-hour GIGT to gestational diabetes mellitus (P < .0001), whereas insulin sensitivity (P = .002) and β-cell function progressively decreased (P < .0001). The strongest independent negative predictors of insulinogenic index/homeostasis model determination of insulin resistance were gestational diabetes mellitus (t = –4.1; P < .0001) and 1-hour GIGT (t = –3.8; P = .0002).
"Like GDM, 1-h GIGT is associated with postpartum glycemia, insulin resistance, and β-cell dysfunction," the study authors write. "Furthermore, its independent association with β-cell dysfunction, in particular, suggests that 1-h GIGT, like GDM, may predict an increased future risk of type 2 diabetes and hence may identify a high-risk patient population that warrants postpartum surveillance."
- Previous research suggests that GIGT at 1 hour is more predictive of negative metabolic outcomes vs GIGT at hours 2 or 3.
- The current study finds that 1-hour GIGT was not related to negative birth outcomes, except for a higher rate of cesarean delivery. However, 1-hour GIGT was associated with higher rates of glycemia; reduced insulin sensitivity; and, in particular, worse β-cell function at 3 months postpartum.
Diabetes Care. 2008;31:1275-1281.