Bitó T et al. (2005) Prediction of gestational diabetes mellitus in a high-risk group by insulin measurement in early pregnancy. Diabet Med 22: 1434–1439

Increased insulin production during pregnancy is a response to the twofold to threefold increase in insulin requirements, which begins at around 16–18 weeks of gestation. Before this, however, hyperinsulinemia might imply underlying insulin resistance and might, therefore, be predictive of subsequent development of gestational diabetes mellitus (GDM).

To investigate this, Bitó and colleagues performed 2-h, 75-g oral glucose-tolerance tests, and measurement of fasting and 2-h-postprandial serum insulin, in 71 women with at least one risk factor for GDM. Tests were performed before week 16 of pregnancy, at gestational weeks 24–28, and again at gestational weeks 32–34 if the earlier test was negative.

There was a strong correlation between serum insulin levels and development of GDM. The majority of women who had elevated serum insulin levels at or before gestational week 16 went on to develop GDM. Sensitivities were 69.2% and 92.3% and specificities 96.4% and 85.7% for fasting and 2-h-postprandial serum insulin levels, respectively, for prediction of GDM at gestational weeks 24–28. No cases of GDM developed in women who had normal insulin levels at or before gestational week 16. Odds ratios for increased fasting and 2-h-postprandial serum insulin levels, at or before gestational week 16, were 16.6 and 13.3, respectively, for the development of GDM.

In high-risk women, serum insulin determination before gestational week 16 is a reliable indicator of subsequent likelihood of GDM, allowing the earlier introduction of management techniques.