The effect of magnesium sulfate on bleeding time in pregnancy

OBJECTIVE: The bleeding time is one of the most commonly used diagnostic tests to evaluate platelet-related hemorrhagic disorders. Magnesium has been shown in vitro to be a platelet antiaggregant. This study was conducted to evaluate the hypothesis that magnesium sulfate has no effect on the template bleeding time. STUDY DESIGN: The study group consisted of 24 women who required magnesium sulfate in pregnancy. A blood cell count, platelet count, magnesium level, bleeding time, and mean arterial pressure were obtained before and 2 hours after magnesium sulfate infusion. Magnesium sulfate was infused beginning with a 6 gm intravenous bolus followed by 2 gm/hr. A template bleeding time was performed with a Simplate-II (Organon Teknika, Durham, N.C.) device. Two of the authors performed all the bleeding times. Data were analyzed with a paired t test and Wilcoxon rank test. RESULTS: Fifteen (63%) patients received magnesium sulfate for tocolysis or before external cephalic version and nine (37%) for preeclampsia prophylaxis. No differences were found between the normotensive and hypertensive groups regarding maternal age, gestational age, initial bleeding time,or platelet count. Analysis of the entire study group revealed a prolongation of the bleeding time after magnesium sulfate (5.7 ± 1.8 vs 6.6 ± 1.9 minutes, p< 0.05); a lowering of the mean arterial pressure (p< 0.05), and a rise in the magnesium level (p< 0.05). Four patients (16.7%) had a postmagnesium bleeding time>9 minutes. CONCLUSION: Magnesium sulfate appears to prolong the bleeding time in pregnancy. The clinical significance remains to be determined.