Overweight is associated with impaired β-cell function during pregnancy: a longitudinal study of 553 normal pregnancies
ObjectiveTo monitor β-cell function and insulin sensitivity longitudinally in a large cohort of pregnant women to elucidate mechanisms that influence glycemic control in pregnancy.Design and methodsFive hundred and fifty-three pregnant Scandinavian women underwent 75 g oral glucose tolerance test (OGTT) at weeks 14–16 and 30–32. Insulin sensitivity (Matsuda index) and β-cell function (ratio of AUCinsulin to AUCglucose, AUCins/glc) were calculated from 520 complete tests, and subsequently β-cell function was adjusted for insulin sensitivity, rendering an oral disposition index (DIo).ResultsEleven women (2.1%) had gestational diabetes mellitus (GDM1) at weeks 14–16, and 49 (9.4%) at weeks 30–32 (GDM2), which is higher than that previously reported in this region. In the subdivision of OGTT, more overweight (body mass index>25) was found in glucose-intolerant groups (glucose-tolerant women (normal glucose tolerance, NGT) 38 versus GDM2 women 58 and GDM1 women 82%, P<0.005). In early pregnancy, insulin sensitivity was lowest in GDM1, intermediate in GDM2, and highest in NGT. In late pregnancy, insulin sensitivity decreased in all groups, most in gestational diabetes. β-cell function demonstrated minor shifts during pregnancy, but when adjusted for decreasing insulin sensitivity, DIo levels fell by 40% (P<0.001). DIo was significantly attenuated relative to glucose intolerance (GDM1 25% and GDM2 53%) during pregnancy. In overweight women, DIo levels were lower throughout pregnancy (P<0.001 versus normal weight women), this reduction was significant (P<0.01) in both NGT (21–25%) and GDM2 subjects (26–49%).Conclusionβ-cell function adjusted for insulin sensitivity (DIo) deteriorated during pregnancy in both glucose-tolerant and glucose-intolerant women. The failure to compensate the decrease in insulin sensitivity was accentuated in overweight women.