1. A study on seven Caucasian glucose-tolerant women with previous gestational diabetes and seven matched control subjects is presented. The insulin response to oral glucose, insulin sensitivity and fasting glucose production rates were measured by using a 75 g oral glucose tolerance test, an insulin tolerance test and a non-radioactive tracer, [6,6-2H]glucose, respectively.
2. Fasting plasma glucose levels were similar between the women with previous gestational diabetes and the control subjects (4.8 ± 0.3 versus 4.7 ± 0.2 mmol/l), as were fasting plasma insulin levels (median 4 m-units/l, range 1–13 m-units/l versus median 4 m-units/l, range 1–24 m-units/l). After oral glucose the 60 min plasma glucose levels in the women with previous gestational diabetes were significantly higher (8.5 ± 0.6 versus 6.7 ± 0.8 mmol/l, P < 0.05), whereas the plasma insulin level was significantly lower at both 30 min (median 23 m-units/l, range 4–47 m-units/l versus median 55 m-units/l, range 23–100 m-units/l, P < 0.02) and at 60 min (median 23 m-units/l, range 4–43 m-units/l versus median 60 m-units/l, range 16–126 m-units/l, P< 0.02).
3. Insulin sensitivity, expressed as the slope of the regression line of plasma glucose level against time after intravenous infusion of insulin (0.05 unit/kg), was similar in the women with previous gestational diabetes and the control subjects (mean slope, −0.17 ± 0.01 versus −0.17 ± 0.01).
4. Fasting glucose production rates were similar in the women with previous gestational diabetes and the control subjects (2.2 ± 0.3 versus 1.9 ± 0.1 mg min−1 kg−1).
5. Women with previous gestational diabetes, a group at risk of future non-insulin-dependent diabetes, have abnormalities of insulin release at a time when insulin sensitivity and fasting glucose production are normal.