The healthy weight gain for a pregnant woman is between 10kg and12.5kg. However, this depends on your BMI before you becoming pregnant. If your BMI is less than 18.5, it means that you are underweight and you need to gain between 13 kg and 18 kg. If your BMI is between 18.5 and 24.9, it means that you have a normal weight, and you can gain between 11 kg and 16 kg during pregnancy. If your BMI is between 25 and 29.9, it means that you are overweight, and you need to limit your pregnancy weight gain somewhere between 7kg and 11kg. If your BMI is over 30, it means that you are obese, and you need to limit the weight gain between 5kg and 9kg.

If you are overweight or obese, its not advisable that you start diet during pregnancy. Instead, a healthy and balanced diet should help you achieve healthy weight gain during pregnancy. Check here for what food are good for pregnant women.