Sample size calculation
overweight
OBESE
The sample size was calculated based on CS rate, which is the primary outcome of this trial. According to previous studies, the difference of CS rate between proper and improper gestational weigh gain of overweight or obese pregnant women is 15–20%. 15% was taken for a two-sided test (α = 0.05 and β = 0.01). The sample size was calculated with the formula n = 2pq(Zα + Zβ)