Differences in pregnancy outcomes and characteristics between insulin- and diet-treated women with gestational diabetes

BACKGROUND Our aim was to evaluate the difference in pregnancy outcomes and characteristics between insulin- and diet-treated women with gestational diabetes (GDM). METHODS Retrospective analysis of the medical files from 2010-2013 of women with GDM diagnosed with the Carpenter & Coustan criteria attending two clinics, one in a university and another in a non-university hospital. Characteristics associated with insulin use were analyzed. Multivariable logistic regression was used to adjust for confounders. For women attending the university hospital, indices of insulin sensitivity such as the reciprocal of the homeostasis model assessment of insulin resistance (1/HOMA-IR) and an index of beta-cell function, the Insulin Secretion-Sensitivity Index-2 (ISSI-2) were calculated. RESULTS Over a 4 year period, 601 women were identified with GDM of whom 22.9% were obese at first prenatal visit. 24.2% needed insulin. Insulin did not prevent adverse outcomes, as women on insulin had higher rates of large-for-gestational age infants (LGA) (28.5% vs. 13.1 %, p < 0.0001) and more cesarean sections (44.1% vs. 27.0%, p = 0.001), remaining significant after adjustment for confounders. Compared to diet-treated women, women on insulin more often had an ethnic minority background (33.3 % vs. 21.6%, p = 0.004), more often had a history of GDM (21.5% vs. 10.4%, p = 0.002), were more often multiparous (59.3% vs. 47.6%, p = 0.044) and were diagnosed with GDM earlier in pregnancy (weeks 25.3 ± 4.9 vs. 27.1 ± 3.7, p < 0.0001). When undergoing an oral glucose tolerance test, women treated with insulin had a higher fasting glycaemia (97.6 ± 18.8 vs.87.7 ± 10.3, p < 0.0001), a higher 1-hour glycaemia (197.7 ± 30.1 vs.184.5 ± 25.8, p < 0.0001), a higher 2-hour glycaemia (185.2 ± 28.5 vs. 175.0 ± 22.8, p < 0.0001), more often 3 and 4 abnormal values (58.1% vs. 37.8%, p < 0.0001 and 24.8% vs. 7.7%, p < 0.0001) and higher HbA1c levels (5.5 ± 0.6 vs 5.2 ± 0.5, p < 0.0001). ISSI-2 (1.3 ± 0.5 vs. 1.7 ± 0.5, p < 0.0001) and 1/HOMA-IR [0.01 (0.001-0.002) vs. 0.02 (0.01-0.03), p = 0.027] were lower in women on insulin. Women on insulin more often received corticoids in preparation of preterm delivery (11.0% vs. 2.4%, p < 0.0001). CONCLUSION Compared to diet-treated women with GDM, women treated with insulin have a higher risk profile, impaired beta-cell function and lower insulin sensitivity. Rates of LGA and cesarean sections were higher in insulin-treated women.