The 33-year-old singer had sparked pregnancy rumours a few days after getting engaged to film producer boyfriend Matthew Rutler, reported People magazine.
"Christina and Matt have been together a long time and always talked about taking the next steps: marriage and growing a family together. They've been through a lot and are very close," a source said.
Aguilera, who already has a son Max, 6, from her previous relationship, is apparently happy that he would have a sibling to grow up with.
"Max has always wanted a little brother or sister. That's something really exciting to them - that he will have a playmate. Christina is really close to her sister and Matt has siblings so they are so happy that Max will have the same experience," the source added.