Aim: The aim of this study was to assess the effect of magnesium sulfate as a potent antihypertensive agent in patients with severe pregnancy induced hypertension (PIH).

Methods: To assess the antihypertensive effect of magnesium sulfate, we retrospectively analyzed 27 women who were administered magnesium sulfate for seizure prophylaxis without any other antihypertensive agents. Average blood pressure was compared before and after administration.

Results: Blood pressure after administration (155±9.5/96±8.4 mmHg) was significantly lower than that before administration (166±8.2/102±8.0 mmHg) (P<0.01). An antihypertensive effect was observed in 59.3% (16/27) of patients (“effective cases”). Among the effective cases, an adequate effect was observed in 14 patients and an excessive effect in two patients. The maximum antihypertensive effect was achieved just after initial loading and was maintained until delivery, as well as 2 h after loading in most effective cases. In patients aged ≥40 years, the proportion of effective cases (16.7%, 1/6) was significantly lower than that among patients aged <40 years (71.4%, 15/21; P=0.016). The proportion of effective cases among patients with early-onset PIH (16.7%, 1/6) was also significantly lower than that among patients with late-onset PIH (71.4%, 15/21; P=0.016).

Conclusion: We demonstrated that magnesium sulfate has an antihypertensive effect in patients with severe PIH. However, this effect was not sufficient for controlling the blood pressure of patients aged ≥40 years or those with early-onset PIH.