A Randomized Clinical Trial of Oral Magnesium Supplementation In Pregnancy for the Prevention of Preterm Birth and Perinatal and Maternal Morbidity

The investigators will complete a multicenter double-blind, placebo-controlled randomized clinical trial of oral Mg++citrate supplementation.

Setting: (1) Instituto de Medicina Integral Prof. Fernando Figueira (IMIP), Recife-Pernambuco: IMIP maintains the largest hospital in Brazil exclusively dedicated to Brazilian Health System, [Sistema Único de Saúde] (SUS). IMIP has 1,032 beds and performs more than 2,000 clinical daily visits. IMIP enrolls about 6,000 deliveries per year and has an obstetric intensive care unit. IMIP is a teaching hospital (degree programs in medicine, nursing, nutrition, physical therapy, pharmacology and psychology and postgraduate - residency, master and doctoral) and is a reference center to woman assistance in Northeast Brazil by the Ministry of Health of the Federal Government. (2) Dom Malan Hospital (HDM), Petrolina-Pernambuco: HDM assists the population of about 1 million people in 55 municipalities of Pernambuco, Bahia and Piauí States. HDM assists about 1,500 pregnant women monthly in emergency service and performs an average of 528 prenatal visits including high-risk pregnancy (±35%). HDM enrolls about 600 deliveries/month and also has an obstetric intensive care unit. HDM has a teaching program for medical and nursing students and also develops a residence program.

Data collection will be conducted from March 2014 to August 2015. Study population will be all pregnant women since they started their prenatal care visits at IMIP and/or HDM before 20th gestational week.

At a sample size of 1000 women assigned to placebo and 2000 women assigned to Mg++ citrate, with power of 80% and a 2-sided P-value of 0.05, we will be able to detect at least a 22% relative risk reduction in the primary perinatal composite outcome, assuming a primary perinatal composite outcome rate of 18% in the placebo group and 14% in the Mg++ group. In Recife there are 25,000 births a year. Of these 25,000, at least 30% (7,500) would attend one of the study prenatal clinics, & of those 7,500, 60% (4,500) would meet ≥1 of the eligibility criteria. With a participation rate of 50%, 2,250 women can be recruited in a year, thus requiring 1.25 years to recruit all women, and 2 years ascertain all primary outcome events.

A systematic sample will be obtained from low risk pregnant women who begin prenatal care visits before 20th gestational week at IMIP or HDM, during the study period.