Imdad et al. BMC Public Health 2011, 11(Suppl 3):S18 http://www.biomedcentral.com/1471-2458/11/S3/S18 Table 1 Characteristics of included studies Study (ref) Country Target population Page 5 of 13 Baseline Dose of Duration of GRADE Calcium intake Supplementation supplementation quality as Low (Cumulative (< 900 mg/day), dose) Adequate (>900g/day), Not specified) Belizan et al Argentina 1991[37] Kumar et al India 2009 [38] L-Jaramillo Ecuador et al. 1989 [41] L-Jaramillo Ecuador et al. 1990 [40] L-Jaramillo Ecuador et al.1997 [39] Niromanesh Turkey et al. 2001 [42] Purwar et al. India 1996[43] Villar et al. 2006 [44] Taherian et al. 2002 [46] Wanchu et al. 2001 [45] Multicenter trial (Argentina, Egypt, India, Peru, South Africa and Vietnam) Iran India Nulliparous pregnant women, < 20 weeks gestation. No comorbid Primigravida women with gestational age between 12-25 weeks Nulliparous pregnant women, < 24 weeks of gestation. No comorbid Nulliparous pregnant women in 28-30 weeks of gestation with positive roll over test Teenage (< 17.5 years) Nulliparous pregnant women < 20 weeks gestation. No comorbids or addiction 28-32 weeks pregnant women with positive roll over test and with at least one risk factor for pre-eclampsia. No chronic medical condition Nulliparous pregnant women < 20 weeks of gestation. No cormorbid Primiparous women < 20 weeks of gestation. No comorbids Nulliparous pregnant women < 20 weeks of gestation. No comrbids Nulliparous pregnant women < 20 weeks of gestation. No known comorbids Low Low Low Low Low Low Low Low Low 2 g/day 2 g/day 2 g/day 2 g/day 2 g/day 2 g/day 1.5 g/day 500 mg/day 2 g/day < 20 weeks of pregnancy till delivery 12-25 weeks of pregnancy till delivery 23 weeks of pregnancy till delivery 28-30 weeks of pregnancy till delivery 20 weeks of pregnancy till delivery 28-32 weeks of pregnancy till delivery 20 weeks of pregnancy till delivery From enrollment till delivery From enrollment till delivery From enrollment till delivery High High Moderate Moderate High High High High Moderate Moderate Not specified 2 g/day of calcium group and 25 cases in 4161 participants of control group giving a relative risk of 0.68 (95 % CI 0.48-0.97). A quality grade of ‘low’ was assigned due to low number (<50 events) of events in the intervention and control group. Severe pre-eclampsia The outcome of severe pre-eclampsia was reported by three included trials [44-46] with a 30% reduction in calcium group compared to control, however the results were not statistically significant [(RR 0.70; 95% CI 0.46- 1.05) (Figure 2). There were a total of 4531 participants in calcium group and 4541 participants in control group. There was no heterogeneity in the pooled data. The overall quality grade for this estimate was that of ‘moderate’ level due to lack of placebo in two studies and confidence interval including unity. We did not per- form any subgroup analysis for this outcome due to fewer numbers of studies reporting this outcome. Pre-eclampsia The impact of calcium supplementation during preg- nancy on risk of pre-eclampsia was reported in 10 stu- dies [37-46]. The analysis comprising 5697 women in intervention group and 5708 women in control group showed a reduction of 59% [RR 0.41; 95 % CI 0.24-0.69, random model] in the intervention group compared to control (Figure 3). On visual inspection of the forest plot, five of the included studies were showing a clear benefit. There was a substantial heterogeneity in the pooled data (I2=74), so the random models were used. The reduction was more marked in participants with a higher pre-pregnancy risk of developing gestational hypertensive disorders [RR 0.18, 95 % CI 0.07-0.42, ran- dom model] compared to that of low risk women [RR 0.51, 95 % CI 0.30-0.87]. The overall quality grade for reduction in risk of pre-eclampsia was that of ‘High’ level.