Not all girls grow up to be mothers. Sometimes they choose not to be, and sometimes circumstances take those choices away. A superfluity of cancers and genetic diseases can destroy women’s ovaries. Or treatments like radiation—used to save a woman’s life—can render those egg-producing organs useless. Ovaries also mediate female hormones. Without them, young patients might never go through puberty; grown women could enter menopause early. Today, a team of bio-engineers reported a possible fix: 3-D printed ovaries. Their proof of concept—published in Nature Communications—only works on mice so far, but they could end up replacing the uterus-flanking, chestnut-sized organs in humans, too.