Introduction <p>Pregnancy-induced hypertension (PIH), a major contributor to global maternal morbidity and mortality, is a disorder marked by elevated blood pressure with or without end-organ damage. It is a condition unique to pregnancy that stems from abnormal uteroplacental development, and possibly, altered mineral homeostasis.</p> Objective <p>To determine whether estimating serum calcium (Ca²⁺) and magnesium (Mg²⁺) levels in the late-second trimester can predict PIH later in pregnancy.</p> Material and Methods <p>In this prospective cohort study, 225 normotensive gravid women underwent total serum Ca²⁺ and Mg²⁺ estimations between 20 and 28&#xa0;weeks of gestation and at delivery. They were followed up until 48&#xa0;h after delivery for the development of PIH (preeclampsia, gestational hypertension, eclampsia).</p> Results <p>A total of 52 (23.11%) women developed PIH, of which 14 (6.22%) women had preeclampsia. Although mean (SD) (mg/dL) serum Ca²⁺ (8.79(0.38) vs. 8.78(0.38); <i>p</i> = 0.696) and Mg²⁺ (1.92(0.25) vs. 1.92(0.21); <i>p</i> = 0.669) levels decreased between the second trimester and delivery, levels remained consistently higher in women with PIH. The ROC-AUC of serum Mg²⁺ for predicting PIH and preeclampsia at 20–28 weeks of gestation was 0.577 (95%CI 0.509,0.642); <i>p</i> = 0.09) and 0.647 (95%CI 0.581,0.709; <i>p</i> = 0.041), respectively; for serum Ca²⁺, the values were 0.544 (95%CI 0.476,0.61; <i>p</i> = 0.359) and 0.558 (95%CI 0.491,0.62; <i>p</i> = 0.46), respectively. At a serum Mg²⁺(mg/dL) cut-off value of &gt; 1.9, the sensitivity of predicting preeclampsia was 92.96%, with a NPV value of 98.3%.</p> Conclusion <p>Total serum Ca²⁺ and Mg²⁺ levels decrease from the second to third trimesters of pregnancy. A total serum Mg²⁺ level of &gt; 1.9&#xa0;mg/dL at 20–28&#xa0;weeks of gestation is a relatively inexpensive screening tool that can fairly predict preeclampsia later in pregnancy.</p>