The picture of personal finance for women in the U.S. has shifted in recent decades. One result: Some women are choosing to become single moms, sometimes to multiple children.

While still a minority in the bigger realm of single motherhood, a growing number of those who make this choice are from upper-middle-class and middle-class backgrounds and have more than one child. This is a contrast to years past, when those pursuing single motherhood were often wealthy and typically had one child, researchers say.

Financial...