Effect of magnesium on fetal heart rate variability using computer analysis

Area of Science:

• Obstetrics and Gynecology
• Perinatology
• Pharmacology

Background:

• Magnesium sulfate (MgSO4) is commonly used to manage preterm labor and preeclampsia.
• The effects of therapeutic MgSO4 levels on fetal well-being, specifically fetal heart rate (FHR) patterns, require careful consideration.

Purpose of the Study:

• To investigate the impact of intravenous magnesium sulfate (MgSO4) therapy on fetal heart rate (FHR) parameters in pregnant women.
• To correlate maternal serum magnesium levels with observed changes in FHR variability and accelerations.

Main Methods:

• Doppler fetal heart rate (FHR) tracings were recorded for 1 hour before and 2 hours after MgSO4 administration in 16 women at ≥32 weeks' gestation.
• Maternal serum magnesium (Mg2+) levels were measured.
• FHR parameters, including long-term variability, short-term variability, and acceleration counts, were analyzed using the Oxford Sonicaid System 8000 and compared with Student's t test.

Main Results:

• MgSO4 administration resulted in significant decreases in long-term variability, short-term variability, and total acceleration counts.
• Reduced FHR variability was observed in all cases with maternal serum Mg2+ levels exceeding 4.6 mg/dL.
• Therapeutic maternal serum Mg2+ levels correlated with diminished FHR variability and acceleration counts.

Conclusions:

• Therapeutic maternal serum magnesium levels are associated with significant reductions in fetal heart rate variability and acceleration.
• These findings necessitate careful interpretation of FHR tracings, particularly the resting baseline, in patients receiving MgSO4 therapy.
• Clinicians should be aware of these pharmacodynamic effects when assessing fetal status during MgSO4 treatment.