Serum magnesium in the first week of life in extremely low birth weight infants

Evidence that antenatal administration of magnesium sulfate (MgSO(4)) to women in preterm labor may confer fetal neuroprotection is growing. MgSO(4) crosses the placenta and can affect the neonate. Magnesium homeostasis in extremely low birth weight (ELBW) infants remains to be clarified.

We aimed to assess the natural progression of serum magnesium (Mg) in ELBW infants not exposed to antenatal MgSO(4) during the first month of life.

Laboratory data of a group of ELBW infants born in a tertiary center over a 1-year period were analyzed. Serum Mg was recorded daily for the first week and thereafter each week for a month for each infant. Concurrent calcium, phosphate and alkaline phosphatase were measured.

51 preterm infants (24 female) with a birth weight <1,000 g were included (33 were born at <27 weeks' gestation). The mean magnesium ranged from 0.9 to 1.1 mmol/l over the first week with a minimum of 0.62 mmol/l and maximum of 1.53 mmol/l. Mg rises in the first few days before stabilizing and remains within a narrow range thereafter.

In ELBW infants, Mg tends to rise initially then stabilize and remain normal thereafter. The effect of antenatal MgSO(4) on magnesium homeostasis requires further study.