In general, pregnant women need between 2,200 calories and 2,900 calories a day. A gradual increase in calories as the baby grows is the best bet. Here is an overview of how calorie needs change during each trimester: The first trimester does not require any extra calories. During the second trimester, an additional 340 calories a day are recommended. For the third trimester, the recommendation is 450 calories more a day than when not pregnant.