Imdad et al. BMC Public Health 2011, 11(Suppl 3):S18 http://www.biomedcentral.com/1471-2458/11/S3/S18 Page 6 of 13 Study or Subgroup Taherian 2002 Villar 2006 Wanchu 2001 Calcium Control Risk Ratio Events Total Events Total Weight M-H, Fixed, 95% CI 3 330 6 330 10.8% 0.50 [0.13, 1.98] 35 4151 47 4161 84.7% 0.75 [0.48, 1.15] 0 50 2 50 4.5% 0.20 [0.01, 4.06] Total (95% CI) 4531 4541 100.0% Total events 38 55 Heterogeneity: Chi² = 0.98, df = 2 (P = 0.61); I² = 0% Test for overall effect: Z = 1.74 (P = 0.08) 0.70 [0.46, 1.05] Risk Ratio M-H, Fixed, 95% CI 0.01 0.1 1 10 100 Favours experimental Favours control Figure 2 Effect of calcium supplementation during pregnancy on risk of development of severe pre-eclampsia in developing countries. Gestational hypertension (± proteinuria) The effect of calcium supplementation on gestational hypertension (± proteinuria) was assessed in six studies from developing countries [37,40-44]. A random effect model pooled analysis showed a significant reduction of 45 % in risk of development of gestational hypertension in women receiving calcium supplementation (4919 women in calcium group) as compared to those receiving control (4942 women in control group) [RR 0.55; 95 % CI 0.36-0.85] .On visual inspection of forest plot, four of the included studies were showing a clear benefit in favor of intervention (Figure 4). There was a significant heterogeneity in the pooled data (I2=82%) and the random models were used. The overall grade quality for this estimate was that of ‘High’ level. Women who were at higher risk of development of hypertension Calcium Placebo Risk Ratio Events Total Events Total Weight M-H, Random, 95% CI Year Risk Ratio M-H, Random, 95% CI Study or Subgroup 2.2.1 Low risk women L-Jaramillo 1989 2 55 12 51 7.3% Belizan 1991 15 579 23 588 13.6% Purwar 1996 2 97 11 93 7.2% Wanchu 2001 9 50 6 50 10.8% Taherian 2002 10 330 27 330 13.0% Villar 2006 171 4151 186 4161 16.7% Kumar 2009 11 273 30 251 13.4% Subtotal (95% CI) 5535 5524 82.0% Total events 220 295 Heterogeneity: Tau² = 0.32; Chi² = 23.81, df = 6 (P = 0.0006); I² = 75% Test for overall effect: Z = 2.49 (P = 0.01) 2.2.2 High women risk L-Jaramillo 1990 0 22 8 34 2.9% L-Jaramillo 1997 4 125 21 135 10.2% Niromnesh 2001 1 15 7 15 4.9% Subtotal (95% CI) 162 184 18.0% Total events 5 36 Heterogeneity: Tau² = 0.00; Chi² = 0.36, df = 2 (P = 0.83); I² = 0% Test for overall effect: Z = 3.89 (P = 0.0001) Total (95% CI) 5697 5708 100.0% Total events 225 331 Heterogeneity: Tau² = 0.41; Chi² = 34.98, df = 9 (P < 0.0001); I² = 74% Test for overall effect: Z = 3.35 (P = 0.0008) Figure 3 Effect of calcium supplementation during pregnancy on risk of development of pre-eclampsia in developing countries. 0.15 [0.04, 0.66] 1989 0.66 [0.35, 1.26] 1991 0.17 [0.04, 0.77] 1996 1.50 [0.58, 3.90] 2001 0.37 [0.18, 0.75] 2002 0.92 [0.75, 1.13] 2006 0.34 [0.17, 0.66] 2009 0.51 [0.30, 0.87] 0.09 [0.01, 1.48] 1990 0.21 [0.07, 0.58] 1997 0.14 [0.02, 1.02] 2001 0.18 [0.07, 0.42] 0.41 [0.24, 0.69] 0.01 0.1 1 10 100 Favours experimental Favours control