At the age of thirty-nine, Sarah Kowalski heard her biological clock ticking, loudly. A single woman harboring a deep ambivalence about motherhood, she needed to decide: Did she want a baby if it meant doing it alone? Once she revised her idea of motherhood--from an experience she would share with a partner to a journey she would embark upon alone--the answer proved to be a resounding Yes. She chose to conceive using a sperm donor, but her plan stopped...