Table 2 Subgroup analysis of the risk of gestational diabetes mellitus and vitamin B12

Cohort studies

4

1.46(1.21–1.79)

59.0%

 < 0.001

0.063

-

Subgroup

 Country

  European

1

1.20 (1.00–1.45)

-

-

0.046

0.03

  Asia

1

1.54 (1.41–1.67)

-

-

 < 0.00

  South Asia

2

1.95(1.26–3.03)

0%

0.91

0.003

 Trimester

  First

2

1.38(1.08–1.75)

82.6%

0.016

0.009

0.0039

  Second

1

1.99 (0.98–3.63)

-

-

0.057

  Third

1

1.90 (0.98–3.67)

-

-

0.022

 GDM diagnosis

  IADPSGC

2

1.38(1.08–1.75)

82.6%

0.016

0.009

0.0031

  WHO1999

1

1.90 (0.98–3.67)

-

-

0.022

  Carpenter-Coustan criteria

1

1.99 (0.98–3.63)

-

-

0.046

  Cross-sectional studies

6

0.97(0.76–1.25)

81.6%

 < 0.001

0.691

Subgroup

 Vitamin B12 levels

  high

3

0.77 (0.63–0.94)

48.1%

0.145

0.011

  low

3

1.33 (0.91–1.94)

79.6%

0.007

0.138

 Sample size

   > 500

2

0.82 (0.72–0.93)

0%

0.786

0.002

0.191

   < 500

4

1.02 (0.72–1.67)

84.0%

 < 0.001

0.666

 Country

  European

2

1.52 (0.59–3.86)

87.1%

0.005

0.382

0.249

  Asia

4

0.85 (0.64–1.14)

81.8%

0.001

0.285

 GDM diagnosis

  IADPSGC

3

1.83 (0.51–1.34)

87.1%

 < 0.001

0.447

0.648

  WHO1999

2

1.44 (0.46–4.26)

90.9%

0.001

0.552

  WHO2016

1

0.90 (0.83–1.18)

-

-

0.911

 Trimester

  First

1

0.90(0.83–1.81)

-

-

0.911

0.107

  Second

4

0.88(0.61–1.27)

81.2%

0.001

0.502

  Third

1

1.31(1.03–1.68)

-

-

0.030