Table 2 Risk odds of birth defects related with maternal folic acid supplementation and based on different folic acid timing

Total birth defects

432/167

0.78 (0.66,0.95)

0.011

0.81 (0.66,0.99)

0.044

0.81 (0.67,0.98)

0.033

Congenital heart disease

110/41

0.80 (0.55,1.16)

0.237

0.88 (0.59,1.33)

0.551

0.83 (0.57,1.22)

0.342

Limb anomalies

37/15

0.95 (0.50,1.80)

0.874

0.95 (0.46,1.96)

0.882

0.84 (0.44,1.58)

0.584

Clefts

73/33

0.72 (0.47,1.11)

0.136

0.66 (0.41,1.04)

0.075

0.69 (0.44,1.06)

0.086

Digestive tract anomalies

32/12

0.69 (0.36,1.32)

0.265

1.08 (0.53,2.23)

0.827

0.93 (0.46,1.88)

0.844

Neural tube defects

82/42

0.56 (0.39,0.82)

0.003

0.56 (0.37,0.86)

0.008

0.63 (0.42,0.93)

0.019

Gastroschisis

64/19

1.03 (0.61,1.75)

0.915

1.02 (0.57,1.83)

0.953

0.96 (0.56,1.66)

0.878

 Total birth defects

163/167

0.60 (0.48,0.75)

< 0.001

0.63 (0.49,0.80)

< 0.001

0.66 (0.53,0.83)

< 0.001

 Congenital heart disease

42/41

0.63 (0.41,0.97)

0.036

0.73 (0.45,1.18)

0.197

0.73 (0.46,1.14)

0.167

 Limb anomalies

12/15

0.51 (0.24,1.12)

0.093

0.69 (0.28,1.70)

0.415

0.61 (0.27,1.35)

0.220

 Clefts

22/33

0.47 (0.27,0.82)

0.007

0.45 (0.25,0.82)

0.008

0.46 (0.26,0.80)

0.006

 Digestive tract anomalies

13/12

0.62 (0.27,1.40)

0.251

0.90 (0.38,2.09)

0.798

0.80 (0.35,1.83)

0.597

 Neural tube defects

38/42

0.55 (0.36,0.85)

0.007

0.51 (0.31,0.85)

0.009

0.61 (0.38,0.96)

0.034

 Gastroschisis

30/19

0.97 (0.54,1.73)

0.913

0.99 (0.51,1.91)

0.966

0.94 (0.81,1.73)

0.833

 Total birth defects

97/167

0.82 (0.64,1.06)

0.134

0.89 (0.67,1.18)

0.407

0.85 (0.65,1.11)

0.337

 Congenital heart disease

24/41

0.65 (0.39,1.11)

0.115

0.88 (0.50,1.55)

0.652

0.76 (0.45,1.30)

0.321

 Limb anomalies

10/15

0.94 (0.41,2.18)

0.888

0.98 (0.38,2.52)

0.961

0.97 (0.42,2.23)

0.934

 Clefts

19/33

0.82 (0.46,1.48)

0.515

0.87 (0.45,1.67)

0.668

0.83 (0.46,1.50)

0.532

 Digestive tract anomalies

8/12

0.84 (0.32,2.21)

0.720

1.21 (0.46,3.21)

0.701

1.09 (0.42,2.79)

0.865

 Neural tube defects

16/42

0.43 (0.23,0.81)

0.008

0.56 (0.30,1.06)

0.076

0.58 (0.32,1.06)

0.075

 Gastroschisis

97/167

0.75 (0.34,1.62)

0.463

1.13 (0.51,2.50)

0.755

1.04 (0.49,2.18)

0.924

 Total birth defects

172/167

1.02 (0.82,1.27)

0.870

1.06 (0.83,1.35)

0.671

1.02 (0.82,1.29)

0.838

 Congenital heart disease

44/41

0.90 (0.58,1.39)

0.637

1.16 (0.71,1.91)

0.552

1.03 (0.66,1.63)

0.884

 Limb anomalies

15/15

1.02 (0.50,2.11)

0.949

1.18 (0.51,2.71)

0.670

1.05 (0.50,2.24)

0.893

 Clefts

32/33

0.97 (0.59,1.61)

0.909

0.84 (0.48,1.46)

0.531

0.93 (0.55,1.56)

0.782

 Digestive tract anomalies

11/12

0.92 (0.39,2.17)

0.854

1.32 (0.53,3.28)

0.546

1.02 (0.43,2.39)

0.967

 Neural tube defects

28/42

0.62 (0.38,1.01)

0.055

0.64 (0.37,1.10)

0.105

0.69 (0.42,1.15)

0.151

 Gastroschisis

21/19

1.04 (0.55,1.96)

0.910

1.00 (0.50,2.00)

0.992

0.95 (0.49,1.83)

0.870