Purpose: The objective of this study was to estimate the combined effect of serum ferritin (SF) concentration and free thyroxine (fT4) levels on the risk of gestational diabetes mellitus (GDM).
Methods: Women presented for antenatal care at a tertiary hospital in Shanghai, China were included in this study from December 2012 to March 2014. Women were divided into six groups according to the SF and fT4 level. Multiple logistical regression model was used to estimate odds ratio (OR) among different groups. Relative excess risk of interaction (RERI), the attributable proportion (AP) of the interaction and the synergy index (SI) were applied to evaluate the additive interaction of SF concentration and fT4 level.
Results: A total of 6542 qualifying pregnant women were included in this study. We observed that a high SF concentration in early pregnancy was related to an increased risk of GDM (OR = 1.21, 95%CI: 1.02-1.43); while a low fT4 level was not (OR = 1.18, 95%CI: 0.89-1.58). There is no addictive interaction between SF and fT4 level on the presence of GDM.
Conclusions: The study suggests that only high serum ferritin concentration is associated with an increased risk of GDM in early pregnancy. The level of fT4 in early pregnancy might have no effect on the association between high SF and risk of GDM.
Keywords: Free thyroxine; Gestational diabetes mellitus; Isolated hypothyroxinemia; Serum ferritin.
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