Maternal iron and zinc and preterm labor risk: A nested case-control study based on the Lanzhou Birth Cohort Study (BBCS) in China.

BACKGROUND AND OBJECTIVES: The aim of this study was to investigate the effect of dietary iron and zinc in-take on the risk of preterm labor before and during different trimesters, and to assess whether there is an interaction between iron and zinc intake and the risk of preterm labor. METHODS AND STUDY DESIGN: The study was a nested case-control study of 880 cases and 8017 controls in Lanzhou City, northwest China. Unconditional logistic regression was used to determine the association between dietary iron/zinc intake and the risk of preterm labor and its clinical subtypes. Multivariable-adjusted restricted cubic spline (RCS) modeling was used to explore the non-linear relationship between dietary iron/zinc intake levels and the risk of preterm birth. Lower iron/zinc intake before and during pregnancy was associated with a higher risk of preterm labor and some of its subtypes, and there was a non-linear trend between iron/zinc intake and risk of preterm labor (p non-linear <0.05). A synergistic effect of low iron and zinc intake on the risk of preterm labor was also observed. RESULTS: We observed a significant increase in the risk of preterm labor in women with low dietary zinc intake before and during pregnancy, with a dose-response relationship. Similarly, there was a significant negative association between lower dietary iron intake during pregnancy and preterm labor. In addition, there was a multiplicative interaction between low dietary iron and zinc intake and preterm delivery before pregnancy and during three different periods of pregnancy. CONCLUSIONS: Higher dietary intake of iron and zinc before and during pregnancy may reduce the risk of preterm labor. Low intakes of iron and zinc during pregnancy appear to have a synergistic effect on the risk of preterm labor.