Patriarchy reduced femininity to maternity, and women to motherhood. In the course of the 20th century, the massive incorporation of women into the labor market and economic autonomy, the generalization of the urban society model, and the access to contraceptive methods have meant that having children has become a choice.
In the history of humanity, motherhood was not a choice. Once humans became sedentary, bringing children into a family meant more working hands, children being smaller adults. It was only in the industrial revolution that children began to become what they are now: a dream, a life project, the greatest love, an inheritance.
Many times motherhood is not so much a desire as an obligation, it is what you have learned all your life, it is what is expected of you as a woman, it is the right thing, the common thing. But having a child apart from the romantic side (the greatest and purest love you've ever experienced) is a very serious choice that especially affects a woman's life in dramatic ways.
We are lucky to have reached the top of feminism, women can now vote, study, have a career, decide on their life partner. Now there are family planning clinics and access to contraception. The emancipation of women and their empowerment has critically influenced the decision to become a mother.