There are few studies on the optimal value of pregnancy weight gain for twin pregnancy in China.At present, China has not put forward guidelines for the appropriate value of weight gain in twin pregnancy, and the lack of standards for weight gain during pregnancy in clinical application or disease prevention and control seriously restricts the health management of pregnant women.In order to effectively control a series of adverse consequences caused by improper weight gain of women during twin pregnancy, it is urgent to establish the appropriate value of weight gain during twin pregnancy, which will also fill the gap in this field in China.

Inclusion Criteria:

• 18-45 years
• Twin pregnancy
• pregnancy weeks ≤ 6 weeks

Exclusion Criteria:

• adverse pregnancy history
• kidney disease