The intervention
weight gain
The pregnant women in the intervention group took the smartphone assisted weight management in addition to the usual care. The participants downloaded the App at the hospital or home. The pregnant women were asked to use the App from the establishment of their gestational records at the hospital (6–7 weeks). The App can run in either iOS or Android system. The App has the following main icons (Fig. 
Weight management plan: according to the user’s BMI and gestational week, the system automatically and personally recommends weight gain plan, and indexes of calorie intake and consumption. The indexes are specified in each gestational week and serve as the references of the objectives of daily weight gain, diet and physical exercise.Daily recording: (a) weight recording: the user enters the daily weight, and gets automatic feedback according to the gestational week; (b) diet recording: the user enters the grams and categories of food for each meal. The system automatically calculates the calorie intake; (c) physical excise recording: the user authorizes the App to obtain the pedometer data from the operation system and the App automatically converts them to calorie consumption. The user enters the types of physical activity (PA) and time, and the App calculates the calorie consumption, respectively.Data trend: the App generates the curves of weight, diet and exercise, and inspires the user to follow the weight management plan.Reminder: (a) antenatal care reminder: according to the user’s gestational week, the App reminds the user to take standard antenatal care at the hospital; (b) recording reminder: the App reminds the user to enter daily weight, diet and exercise data.Pregnancy education: according to the user’s gestational week, the App delivers the pregnancy education contents.
The home menu of the App The participants were asked to report their weight, diet and PA via the App at least once a week. We define the termination of the App usage as the gestational weeks in which the patients entered their weight, diet and/or physical activity data for the last time. The period in which the patients were supposed to use the App is the time between the record establishment at hospital and termination of the App usage. We define the adherence as below,
The frequent user is defined as adherence ≧ median of adherence, and the non-frequent user is defined as adherence < median of adherence.