Changes in Fetal Heart Tracing Characteristics after Magnesium Exposure

Abstract

Objective The aim of this study is to describe the changes in term fetal heart tracings after magnesium exposure.

Materials and Methods This was a retrospective cohort study of consecutive women delivering at a gestational age of ≥ 37 weeks with severe preeclampsia, receiving magnesium for seizure prophylaxis. Overall 90 minutes of electronic fetal monitoring (30 before magnesium, 30 during magnesium bolus, and 30 during steady state infusion) was prospectively interpreted by formally trained and blinded research nurses using American Congress of Obstetricians and Gynecologists guidelines. Multivariable analyses were performed using generalized estimating equations, comparing preexposure patterns to bolus, and steady state.

Results Out of the 238 women evaluated, an average decrease of 2.4 beats per minute (p = 0.02) was found after magnesium bolus. This persisted into the steady state (p < 0.01). Minimal/absent variability increased during bolus infusion (odds ratio [OR] 2.40, 95% confidence interval [CI] 1.10–5.62) but corrected by steady state (OR 1.44, 95% CI 0.76–2.80). There were no significant changes in the fetal heart rate (FHR) baseline < 120, tachycardia, or presence of accelerations or decelerations.

Conclusion Exposure to magnesium is associated with a transient decrease in variability and a clinically insignificant decrease in FHR baseline without an increased incidence in bradycardia or category change.

Keywords

electronic fetal monitoring - fetal heart rate - magnesium

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