【目的】妊娠糖尿病患者の2型糖尿病発症のリスク評価に対する75gブドウ糖負荷試験（OGTT）の有用性を検討するため，妊娠糖尿病患者のインスリン分泌能を検討した。【方法】2003年7月から2011年11月に聖路加国際病院に入院した妊娠糖尿病患者682名のうち，出産前後にOGTTを行った36名を対象とし，insulinogenic indexを算出した。【結果】妊娠糖尿病患者の耐糖能は，出産後に改善していた。一方，insulinogenic indexは，出産前と比較し，出産後では有意に低下していた。さらに，出産前のinsulinogenic indexが0.4以上の患者のうち，約半数が出産後に0.4未満に低下したことが明らかとなった。【考察】将来の2型糖尿病発症のリスク予測には，出産前のOGTTの評価だけでは十分といえず，出産後にOGTTを実施し，耐糖能だけでなく，insulinogenic indexを評価することが重要である可能性が示唆された。

[Objective] To investigate whether 75 g glucose tolerance test (OGTT) may predict the risk of diabetes after delivery in women with gestational diabetes mellitus (GDM), insulin secretion dynamics were examined in women with GDM undergoing OGTT. [Methods] A total of 682 women with GDM were admitted to St. Luke’s International Hospital from July 2003 to November 2011. Of these, 36 women who underwent OGTT before and after delivery were included in this study, and their insulinogenic index calculated. [Results] Glucose tolerance was improved in women with GDM after delivery. In contrast, mean insulinogenic index was significantly lower after delivery in these women than before delivery. Moreover, the insulinogenic index was reduced to less than 0.4 after delivery in half of those whose insulinogenic index exceeded 0.4 before delivery. [Conclusions] Our present study suggests that comparing glucose tolerance and insulinogenic index during the OGTT before and after delivery may be important for predicting the future risk of type 2 diabetes in patients with GDM.