Maternal Intake of Magnesium, Calcium, and Calcium Supplements: Association with Preterm Birth Risk in a Nested Case-Control Study

Objective To explore the association between magnesium (dietary), calcium (dietary), and calcium supplements intake levels before and during pregnancy and the risk of Preterm birth (PTB). Methods The study subjects were pregnant women who registered at the Perinatal Medicine Center of Gansu Provincial Maternal and Child Health Hospital between March 2018 and March 2019 and whose birth outcomes could be followed up. After obtaining informed consent and ethical approval, a one-on-one dietary nutrition survey was conducted during pregnancy. A database was established based on overall dietary intake levels for statistical analysis. PTB was used as the outcome variable, and intake levels of different substances during pregnancy were used as independent variables. Unconditional logistic regression model was used to calculate the odds ratio (OR) and its 95% confidence interval (95% CI), in order to analyze the impact of different levels of substance intake on PTB. Multivariate-adjusted restricted cubic spline (RCS) models explored the nonlinear association between dietary magnesium/calcium intake and PTB risk. Results A total of 8897 pregnant women were included in the study, with 880 in the case group and 8017 in the control group. Multivariate logistic regression analysis revealed that low magnesium intake in third trimester and inadequate calcium supplements intake elevate the risk of PTB. Similarly, low calcium intake before and during pregnancy also increases this risk. Moreover, magnesium, calcium, and calcium supplements exert a synergistic effect on the risk of PTB. Conclusion During the third trimester, intake of magnesium and calcium supplements should be increased. Additionally, to prevent PTB, calcium intake should be enhanced preconception and during pregnancy.