S/N

Study design

No. of subjects (Nation)

Sampling for serum 25(OH)D (Trimester/Weeks)

Cut off value for 25(OH)D deficiency/ insufficiency

Results(Maternal vitamin D level vs. incidence of GDM)

Reference

1

Cross

sectional

886 (Spain)

Second trimester

<20 ng/mL

Vitamin D deficiency is associated with GDM, independent of BMI.

[26]

2

Cross

sectional

80 (Turkey)

Second trimester

10 - 20 ng/mL

Serum vitamin D levels in women with GDM are significantly lower than the controls.

[27]

3

Cross

sectional

90 (Iran)

20 - 30 weeks

10 - 20 ng/ml

Serum 25(OH)D level is significantly low in GDM group.

[28]

4

Cross

sectional

78 (Malaysia)

Third trimester

<12 ng/ml

Women with GDM had lower vitamin D status which was associated with ethnicity and less outdoor activity.

[29]

5

Cross

sectional

228

(Philippine)

Second & third trimesters

≤20 ng/ml.

An association found between low level of (≤30 ng/ml) maternal serum vitamin D level and GDM (OR = 0.28; 95% CI = 0.09 - 0.88) but none was evident after adjusting for possible confounders (OR = 0.66; 95% CI = 0.18 - 2.36).

[30]

6

Cross

sectional

723 (Finland)

11 weeks

<50 nmol/L

No association found.

[58]

7

Cross

sectional

1400 (Turkey)

24 - 28 weeks

<20 ng/mL (Severe deficiency)

No association found.

[59]

8

Cross

sectional

80 (Iran)

24 - 28 weeks

<20 ng/dL

No association found.

[60]

9

Prospective cohort

1314 (USA)

26 - 28

25 - 50 nmol/L

Pregnant mothers with 25(OH)D levels of 25 nmol/L may have higher odds of experiencing GDM (OR: 2.2, 95% CI: 0.8 - 5.5).

[31]

10

Prospective cohort

515 (Saudi)

First trimester

<50 nmol/L

GDM risk was significantly higher among vitamin D deficient group (OR: 2.87; Confidence Interval: 1.32 - 6.25; P = 0.008

[32]

11

Prospective cohort

655 (Canada)

06 - 13

<50 nmol/L

Lower first trimester 25(OH)D level is associated with higher risk of developing GDM (OR = 1.48; 95% CI = 1.03 - 2.12), and higher HOMA-IR (r = −0.08; P = 0.03).

[33]

12

Prospective cohort

392 (South India)

12 weeks

<50 nmol/L

Vitamin D deficiency in early pregnancy is significantly associated with developing GDM.

[34]

13

Prospective cohort

890 (Australia)

18 weeks

<30 nmol/L

Second trimester low maternal 25(OH) D levels (<30 nmol/L) are associated with GDM (OR = 14.63, 95% CI = 1.59 - 134.78).

[35]

14

Prospective cohort

2800

(Australia & New Zealand)

15 ± 1 weeks

<50 nmol/L

GDM risk was observed with high (>81 nmol/L) “standardised” vitamin D status when compared to moderate-high (63 - 81 nmol/L)

[36]

15

Prospective cohort

64 (Turkey)

24 - 28

<10 ng/l (Severe deficiency)

25(OH)D levels were negatively correlated with HOMA-IR (P < 0.001).

[37]

16

Prospective cohort

3318 (China)

8 - 14 weeks

<20 ng/ml

Vitamin D deficiency in T₂ was associated with an increased risk of GDM with increased FBG of OGTT.

[38]

17

Prospective cohort

674 (USA)

<16

<50 nmol/L

There was a negative association between 25(OH)D and maternal hyperglycaemia among smokers (OR = 0.30; 95% CI = 0.13 - 0.68) while no association found among non-smokers.

[39]

18

Prospective cohort

1710 (New Zealand)

15

<50 nmol/l

No association found.

[40]

19

Prospective cohort

523 (Korea)

24 - 28 20 - 22 32 - 34

<25 nmol/L

No association found.

[61]

20

Prospective cohort

80 (Egypt)

24 - 28

<20 ng/mL

No association found.

[62]

21

Prospective cohort

785

(Australia)

6 - 14 & 14 - 18

<12.5 nmol/L (Severe deficiency)

No association found.

[63]

22

Prospective cohort

524 (Canada)

17 - 18

<50 nmol/L

No association found.

[64]

23

Prospective cohort

785

(Norway)

15 - 28 weeks

<50 nmol/L

No association found.

[65]

24

Prospective cohort

3110 (China)

First trimester

<20 ng/ml

No association found.

[66]

25

Prospective cohort

938 (Iceland)

11 - 14 weeks

<30 nmol/L

No association found.

[67]

26

Prospective cohort

1516 (China)

11 - 14 weeks

<50 nmol/L

No association found.

[68]

27

Retrospective cohort

8468 (China)

<20 weeks

<20 ng/ml

Vitamin D level > 20 ng/mL can reduce the risk of GDM (OR  =  0.90).

[41]

28

Retrospective cohort

2814 (China)

≤20 weeks

<50 nmol/L

A protective association was found between higher serum 25(OH)D concentrations and GDM (P = 0.003).

[42]

29

Retrospective cohort

7816 (China)

6 - 14 weeks

<20 ng/ml

No association found.

[69]

30

Retrospective cohort

235 (USA)

5 - 12 weeks

<20 ng/ml

No association found.

[70]

31

Nested case control

400 (China)

26 - 28

<25 nmol/L

Subjects with 25(OH)D deficiency had 1.8-fold higher risk of GDM (OR: 1.800, 95% CI: 1.209 - 2.678, P = 0.004).

[43]

32

Nested case control

210 (India)

<20

<20 ng/mL

Women with vitamin D deficiency in early pregnancy were eleven times more likely to have GDM compared to controls (P = 0.001)

[44]

33

Nested case control

335 (Canada)

15 - 18

<75 nmol/l (Insufficient)

Vitamin D insufficiency in early pregnancy is associated with a greater than twofold increase in subsequent gestational diabetes, even after matching and adjusting for race, age, season and weight.

[45]

34

Nested case control

321 (USA)

10 - 14 23 - 31 33 - 39

<50 nmol/L.

Women with persistent vitamin D deficiency at 10 - 14 and 15 - 26 weeks of gestation had a 4.46-fold elevated risk for GDM.

[46]

35

Nested case control

2320

(Canada)

<20 weeks

<30 nmol/L

In smokers, significant increased odds of developing GDM was seen among women with 25(OH)D < 30 nmol/L [aOR = 3.73, 95% CI 1.9, 7.14] compared to non-smokers with 25(OH)D

concentration ≥50 nmol/L.

[47]

36

Nested case control

652 (USA)

16

<20 ng/mL or <50 nmol/L

No association found.

[48]

37

Nested case control

180 (USA)

11 - 14

<50 nmol/L.

No association found.

[71]

38

Nested case control

1191

(Belgium & France)

11 - 15

<10 ng/mL (deficiency) <20 ng/mL (insufficiency)

No association found.

[72]

39

Nested case control

318 (Russia)

8 - 14 & 24 - 32

<20 ng/mL

No association found.

[73]

40

Nested case control

5109

(Australia)

First trimester

<25 nmol/L

No association found.

[74]

41

Case control

120 (Turkey)

26 - 28

<25 ng/mL

Vitamin D deficiency in the second

trimester was inversely correlated with fasting and 1-h plasma glucose after 75 g glucose challenge test (P < 0.001), also low 25 OHD3 levels were associated with insulin resistance.

[49]

42

Case control

60 (Korea)

Third

trimester

<20 ng/mL

Serum levels of 25(OH)D were lower in women with GDM (P < 0.01).

[50]

43

Case control

70 (India)

<28 weeks

<20 ng/ml

Vitamin D deficiency is more frequently associated with GDM than the controls.

[51]

44

Case control

80 (Egypt)

<28 weeks

<10 ng/ml

Serum 25 (OH)D had a significant negative correlation with fasting insulin level (P = 0.05).

[52]

45

Case control

40 (Turkey)

24 - 28

<10 ng/mL

No association found.

[75]

46

Case control

157 (Brazil)

Third

trimester

<10 ng/ml

No association found.

[76]

47

Case control

76 (Central Europe)

24 - 30 weeks

<50 nmol/L

No association found.

[77]

48

Case control

122 (Istanbul)

24 - 28

≤20 ng/ml

No association found.

[78]