Abstract
CONTEXT: Experimental studies suggest that magnesium levels in pregnant women may affect the length of gestation, as magnesium affects the activity of smooth muscle in the uterus. Little is known about the association between magnesium levels or supplementation and the rate of preterm birth. OBJECTIVE: The aim of this systematic review was to summarize the data on magnesium soil levels and preterm birth rates from ecological, observational, and interventional studies. DATA SOURCES: Soil magnesium levels were obtained from US Geological Survey data, and preterm birth rates were acquired from the March of Dimes Foundation. Relevant epidemiological and clinical studies published until April 2019 in peer-reviewed journals were retrieved from PubMed, Google Scholar, and related reference lists. STUDY SELECTION: Original studies published in English, conducted in humans, and in which magnesium (dietary/supplemental intake or biomarkers) was an exposure and preterm birth was an outcome were included. DATA EXTRACTION: Eleven studies were included in the systematic review. Meta-analysis was performed on 6 studies. Overall relative risk (RR) and corresponding 95%CIs for risk of preterm birth in relation to magnesium supplementation were estimated by a random-effects model. RESULTS: The ecological study revealed an inverse correlation between magnesium content in soil and rates of preterm birth across the United States (r = -0.68; P < 0.001). Findings from 11 observational studies generally support an inverse association between serum magnesium levels and rates of preterm birth. Of the 6 eligible randomized controlled trials, which included 3068 pregnant women aged 20 to 35 years and 352 preterm infants, the pooled RR was 0.58 (95%CI, 0.35-0.96) for women in the magnesium supplementation group compared with women in the control group. CONCLUSIONS: Accumulated evidence from ecological, observational, and interventional studies consistently indicates that adequate magnesium intake during pregnancy may help reduce the incidence of preterm birth.