Inositol is a type of food additives, which plays an important role in insulin signal pathway and is related to insulin sensitivity. Our randomized, double-centered, placebo-controlled study is planned to recruit 360 pregnant women who is in high risk for gestational diabetes. They will be assumed randomly 1 g of D-chiro inositol per day or placebo from 12-16th gestational weeks until Oral Glucose Tolerance Test (OGTT) at 24-28th gestational weeks. Perinatal outcomes about delivery time, neonatal weight will be registered.

Inclusion Criteria:

• During 12-16 weeks gestation
• Meet any of the following: prepregnancy BMI > 24, family history of diabetes (type 1 or 2), GDM history, history of delivering macrosomia, gestational history of stillbirth;
• Willing to participate

Exclusion Criteria:

• Type 1 or type 2 diabetes mellitus diagnosed before pregnancy
• Multiple gestation
• Mental or cognitive impairment cannot complete the study

The random number table is compiled by the investigator who is specially responsible for grouping and saved. The investigator packaged and coded drugs according to random number table, and recorded. The packaged and numbered drugs are stored in the enrollment office.

When the participants meet the inclusion criteria by care providers (doctors), the enrollment office generates a random number for each subject. The participants received the package of drugs according to their random number, and the random number was recorded in the record book.

If there are adverse events or the subjects request to withdraw from the trial, the investigator should uncover the blind.