First Author’s Name

Year/Country/ Study design

Sample size

Inclusion/Exclusion Criteria

Results

Chen, Q.

2019/China/ Case-Control

9556: 1464 (15.3%) GDM cases and 8092 (84.7%) non-GDM controls

Inclusion criteria: women aged 18 years or older with gestational age of 20 weeks or more and without mental illness

Exclusion criteria: previous DM, Gestational age < 24

Higher folate and potassium level in the vitamin supplements increased the risk of GDM.

Increased FA level aggravates the effects of vitamin B₁₂ deficiency and exacerbates insulin resistance.

Cheng, G.

2019/China/ Cohort

950 (GDM cases were 10.2%)

Inclusion criteria: infants had health care records in the CHMIS; mothers and infants’ guardians agreed to participate and signed the written informed consents; and mothers took FA supplements at a dose of 400 mcg/day before, and during, pregnancy.

Exclusion criteria: mothers had a history of mental illness or brain disease, diabetes before pregnancy; multiple pregnancy; congenital abnormalities in the newborn

FA supplementation for ≥3 months before pregnancy was associated with an increased risk of GDM (aRR: 1.72; 95% CI: 1.17 - 2.53)

Huang, L.

2019/China/ Cohort

326: 33 (10.1%) had GDM

N/A

After adjusting for confounding factors, the aOR of GDM comparing taking folic acid for >90 days with taking folic acid for ≤60 days was 3.45 (95% CI: 1.01, 11.8)

Li, Q.

2019/China/ Cohort

4,353: 8.6% had GDM

Exclusion criteria: those with diabetes, multiple pregnancies, abortions, without reliable OGTT or folic acid supplementation values

FA supplement use >800 mg/day from pre-pregnancy through mid-pregnancy was associated with the development of GDM

Zhang, H.

2019/China/ Cohort

5165: 604 (11.7%) had GDM

Exclusion criteria: women with one of the following

Conditions: pre-existing type 1 and type 2 DM or GDM, thyroid disease, hypertension, asthma and systemic lupus erythematosus.

First trimester exposure to ai polluted with SO₂ increased the risk of GDM, especially if between the 4^th and 10^th weeks of gestation, and if using FA supplements.

Zhu, B.

2019/China/ Cohort

1938: 249 (12.8%) had GDM

Inclusion criteria: Women who had either used FA supplements or never used any vitamin supplements

Higher risk of GDM was found with daily FA supplementation during the first trimester (aOR = 2.25 [95% CI 1.35 - 3.76])