Table 2 Meta-analysis of associations between the ESR1 gene polymorphism and severe and mild preeclampsia

polymorphism	Comparison	No. of	Test of associations		Test of heterogeneity		Model	Egger’s test	Sensitivity analysis
		Studies	OR (95%CI)	P value	I²(%)	P value		P value	OR (95%CI)	P value
-397 T/C PvuII (rs2234693)
Severe preeclampsia
	C vs. T	7	1.02(0.87,1.21)	0.796	0	0.892	F	0.880	0.99(0.83,1.20)	0.960
	CC+CT vs. TT	7	1.05(0.81,1.37)	0.713	0	0.890	F	0.520	0.99(0.74,1.32)	0.917
	CC vs. TT+CT	7	1.01(0.76,1.33)	0.963	0	0.935	F	0.438	1.01(0.74,1.35)	0.982
	CC vs. TT	7	1.04(0.74,1.45)	0.828	0	0.900	F	0.874	0.99(0.68,1.43)	0.953
	CC vs. CT	7	0.99(0.74,1.33)	0.954	0	0.949	F	0.325	1.01(0.74,1.39)	0.941
Mild preeclampsia
	C vs. T	5	1.02(0.86,1.21)	0.783	0	0.426	F	0.919	0.99(0.83,1.20)	0.967
	CC+CT vs. TT	5	1.08(0.83,1.43)	0.562	0	0.627	F	0.996	1.02(0.75,1.38)	0.907
	CC vs. TT+CT	5	0.98(0.74,1.30)	0.884	7	0.367	F	0.696	0.97(0.71,1.33)	0.850
	CC vs. TT	5	1.03(0.73,1.45)	0.888	0	0.431	F	0.888	0.97(0.66,1.43)	0.878
	CC vs. CT	5	0.95(0.70,1.29)	0.738	0	0.416	F	0.811	0.93(0.69,1.34)	0.822
-351 A/G XbaI (rs9340799)
Severe preeclampsia
	G vs. A	4	1.10(0.91,1.34)	0.331	0.4	0.390	F	0.636	1.14(0.91,1.43)	0.255
	GG+GA vs. AA	4	0.97(0.74,1.28)	0.846	5.8	0.407	F	0.205	1.01(0.74,1.36)	0.979
	GG vs. AA+GA	4	1.67(1.10,2.55)	0.017^a	30.6	0.228	F	0.808	1.81(1.12,2.93)	0.016¹
	GG vs. AA	4	1.43(0.90,2.28)	0.125	14.2	0.321	F	0.925	1.54(0.91,2.60)	0.106
	GG vs. GA	4	1.81(1.17,2.82)	0.008^a	38	0.184	F	0.858	1.97(1.19,3.27)	0.008¹
Mild preeclampsia
	G vs. A	3	1.03(0.83,1.28)	0.764	0	0.563	F	0.337	1.04(0.81,1.35)	0.747
	GG+GA vs. AA	3	0.90(0.67,1.22)	0.494	35.1	0.214	F	0.483	0.91(0.65,1.29)	0.613
	GG vs. AA+GA	3	1.13(0.67,1.91)	0.647	0	0.545	F	0.212	1.04(0.54,2.01)	0.897
	GG vs. AA	3	1.12(0.64,1.97)	0.697	0	0.858	F	0.047	1.11(0.56,2.23)	0.759
	GG vs. GA	3	1.15(0.67,1.96)	0.619	14.3	0.311	F	0.202	1.03(0.52,2.02)	0.941

↵a P<0.05.
Abbreviations: OR: odds ratio; 95% CI: 95% confidence interval; F: fixed effects model; R: random effects model; No.: number.