Timing of administration of antenatal magnesium sulfate and umbilical cord blood magnesium levels in preterm babies.

BACKGROUND

The optimum timing of administration of magnesium sulfate (MgSO4) in relation to delivery is not known. The general consensus is to achieve administration to the mother at least 4 hours prior to preterm delivery.

OBJECTIVE

To investigate potential predictors of umbilical cord blood magnesium (Mg) concentrations, in particular, timing of antenatal MgSO4 administration in relation to delivery.

STUDY

DESIGN

A prospective observational study of infants delivered at less than 32 weeks' gestational age. Cord bloods samples were collected at delivery and Mg levels analyzed.

RESULTS

Of the 81 included cases, five received no antenatal MgSO4, 65 received a 4 g bolus only, and 11 received a 4 g bolus and 1 g/hour infusion. The median time of bolus administration before delivery was 104 minutes (IQR: 57-215). The mean magnesium level was 0.934 mmol/L in the no antenatal MgSO4 group, 1.018 mmol/L in the bolus only group, and 1.225 mmol/L in the bolus and infusion group (p < .05). In the bolus only group, the highest mean magnesium concentration (1.091 mmol/L) was achieved with administration 1-2 hours before delivery, but the difference was small and not statistically significant. On multiple regression analysis, lower birthweight Z scores and gestational age were independently associated with higher cord blood Mg levels.

CONCLUSIONS

In the bolus only group, the highest mean Mg levels were observed with administration 1-2 hours before delivery, but the findings were not statistically significant. Compared to the rest of the cohort, higher Mg levels were found when a bolus was followed by an infusion. Following a MgSO4 bolus, some growth restricted extremely preterm babies may have higher Mg levels than would be otherwise expected.