Studies have shown that the use of IV MgSO4 administered in pregnant women prior to 30 weeks’ gestation decreases the risk of death and cerebral palsy (CP) in offspring. However, it is unclear what effect later administration of MgSO4 may have on the developing fetus.

Investigators conducted a multicenter, randomized clinical trial (known as the MAGENTA trial) in 24 Australian and New Zealand hospitals from January 2012 to April 2018 to determine whether administration of MgSO4 at 30 to 34 weeks’ gestation reduced death or CP at age 2 years.

The study included pregnant women at risk of preterm birth between 30 to 34 weeks’ gestation who were expected to deliver within the next 24 hours and who did not have a contraindication to the use of MgSO4. Contraindications included respiratory depression, hypotension, absent patellar reflexes, kidney failure, or myasthenia gravis. Patients were also excluded if they were receiving MgSO4 for preeclampsia.

Patients were randomized to receive MgSO4 4 g or placebo IV for 30 minutes. The children of consenting mothers were assessed by a pediatrician using the Bayley Scales of Infant Development (BSID-III) as close as possible to age 2 years. These children underwent a neurological examination to determine the presence of CP, which was primarily diagnosed by the loss of motor function and abnormalities of muscle tone and power with gross motor dysfunction as determined by the Gross Motor Function Classification System or with other disabilities; vision and hearing assessment; and measurements of height, weight, head circumference, and blood pressure. The children also underwent a psychological assessment as incorporated into the BSID-III. Caregivers completed a questionnaire focusing on the child’s health, use of healthcare services since birth, and behavioral issues.

The primary outcome was death (defined as stillbirth, death of the live-born infant before hospital discharge, or death after hospital discharge before age 2 years) or CP. There were 36 secondary outcomes that involved the pregnant patient, the infant, and the child.

A total of 1,433 pregnant patients (mean age 30.6 years) were enrolled in the study, which corresponded to 1,679 infants who were alive at study entry. Of these, 729 pregnant patients (51%) and 858 infants received MgSO4 and 704 pregnant women (49%) and 821 infants received placebo. Among the infants, 40% were born at 30 to <32 weeks’ gestation, 55% were born at 32 to <34 weeks’ gestation, and 5% were born at >34 weeks’ gestation.

The investigators found that there was no difference in the occurrence of death or CP among children in the MgSO4 (3.3%) or placebo (2.7%) group, P = .57. There were 12 deaths by age 2 years in the MgSO4 group versus seven deaths in the placebo group; this was also not statistically different (P = .40). Similarly, there was no difference in the proportion of children who had CP between the groups (1.6% in the MgSO4 group vs. 1.7% in the placebo group, P = .96).

Of the secondary outcomes in the offspring, the only differences were in the likelihood of children exposed to magnesium being more likely to have overall behavioral scores within the clinical problem range (adjusted relative risk [RR] 1.66, P = .04), and those children who received MgSO4 were less likely to develop neonatal respiratory distress syndrome (adjusted RR 0.85, P = .01; adjusted number needed-to-treat [NNT] = 21) or chronic lung disease (adjusted RR 0.69, P = .04; adjusted NNT = 37).

Of the secondary outcomes in the mother, infusion-related, noncardiac, or respiratory adverse events were more common in the MgSO4 group (adjusted RR 3.76, P <.001) and more often led to treatment discontinuation. Significantly fewer pregnant adults in the MgSO4 group had a cesarean section (adjusted RR 0.91, P = .03; adjusted NNT = 19), but the post-hoc analysis did not find a between-group difference in the indications for the cesarean delivery. There was a trend for more women in the MgSO4 group to experience a major postpartum hemorrhage (adjusted RR 1.98, P = .05). However, the study had limited power to detect small between-group differences.

The investigators concluded that IV MgSO4 administered between 30 to 34 weeks’ gestation did not affect overall survival or the development of CP as assessed at 2 years post-birth.

The information in this study is beneficial for pharmacists who manage patients in labor and delivery and can be used to help promote rational pharmacotherapy.

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