Eating for two? Here are some tips for maintaining a healthy diet for you and the baby: Calories: First trimester - About 1,800 calories per day Second trimester - About 2,200 calories per day Third trimester - About 2,400 calories per day *Calories based on the average weight and BMI for surrogates. Weight gain: Worried about the weight you're gaining? Don't put too much thought into it, here are some of the reasons you're gaining pounds: 7.5 pounds: Average baby's weight 7