Women who want to conceive but cannot often find it an emotionally wrenching experience.

Because scientists believe that women produce only a limited number of eggs before menopause, women face the predicament of having few options. A new study, however, has revealed a possible way to replenish this numbered reserve.

Researchers at Massachusetts General Hospital isolated stem cells in adult ovaries that could potentially become eggs. They first isolated stem cells in rat ovaries in 2004, called oogonial stem cells. OSCs have a protein on their surface called DDX4. Using fluorescent antibodies that bind to this marker protein, they isolated OSCs from mouse ovaries using a cell sorting machine called a Fluorescence Activated Cell Sorter. These cells not only went on to become eggs, but could be fertilized with sperm and become embryos.

Recently, the team was able to apply the same technology to donated human ovaries from Japanese women undergoing gender reassignment surgery. Just as with the mice, researchers isolated OSCs and grew them in a Petri dish until they became immature eggs, called oocytes. When implanted in mice that had human ovarian tissue grafted inside, they matured into eggs, as confirmed by several surface markers they expressed.

U.S. laws forbid fertilization of human eggs in research, so it wasn’t possible to determine whether the eggs could actually develop into embryos. Even if they could, there’s still the question of whether they would be viable embryos capable of producing healthy babies.

Researchers said the same technology could also be used to boost the health of a woman’s existing eggs by transferring mitochondria, the powerhouse of a cell, from OSCs, making the renewed eggs more capable of fertilization. More work would have to be done on both approaches to determine if either actually works.

Only a very small number of cells were isolated in this study, of which only a few became fertilized and produced minimally formed embryos. In mice, the OSCs make up only about 0.014 percent of all cells in the ovary. In addition, many cells grown in the laboratory developed abnormalities, an important problem that would have to be overcome.

What’s provocative about this study is that it shows technology can stimulate new egg production for infertile women. More importantly, it suggests that perhaps women retain the potential to produce eggs later in life, which goes against what scientists have always believed — that egg production is lost soon after birth.

While women start with 1 million eggs, by age 51, they end up with few or none. Having the ability to produce new eggs would make motherhood possible for older women and for some of the 15 percent of reproductive-age couples who are infertile — that’s up to 10 million couples in the United States, of whom about 2 million seek infertility treatments.