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Objective: Magnesium sulfate (MgSO 4 ) is the most commonly used tocolytic agent in the US and is also employed as a prophylactic agent against seizures in pre-eclamptic women. MgSO 4 crosses the placenta and its concentration in the newborn usually exceeds that of maternal levels. The purpose of this study was to explore the relationship between antenatal exposure to MgSO 4 and the incidence of patent ductus arteriosus (PDA) in extremely low birth weight infants.Study design: A total of 954 neonates with birth weights between 500 and 1000 g, born at the University of Miami/Jackson Memorial Hospital between January 1995 and December 2004 and surviving for more than 3 days, were followed until death or discharge from the hospital. The incidence of PDA in infants exposed to MgSO 4 was compared with those not exposed and comparisons were also made between infants exposed to different maternal doses of MgSO 4 .Results: The incidence of PDA was significantly higher in the group of infants exposed to MgSO 4 compared with the unexposed control group (67 vs. 60%, P<0.018). When stratified by gestational age the differences were significant only in the group of infants with a gestational age of X26 weeks (58 vs. 49%, P<0.039). Logistic regression analysis to adjust for co-variables indicated an increased risk of PDA with higher doses of MgSO 4 (odds ratio 1.33 confidence interval (CI) 1.12 to 1.58, per 50 g of MgSO 4 ). Conclusion:Antenatal exposure to MgSO 4 is associated with a higher risk of PDA in extremely low birth weight infants and this effect is more significant and dose-related in more mature infants.

The results of this study suggest that the addition of pressure support as a supplement to synchronized intermittent mandatory ventilation during the first 28 days may play a role in reducing the duration of mechanical ventilation in extremely low birth-weight infants, and it may lead to a reduced oxygen dependency in the 700- to 1000-g birth weight strata.

Preterm infants exposed to chorioamnionitis have an increased incidence of early tracheal colonization. This early tracheal colonization may predispose them to develop BPD.