The procedure is still a long way from becoming common practice, and Atala's team declined to estimate its cost.

"Even if we were able to add up the cost of materials and researchers’ time, the costs to treat these first four patients wouldn’t correspond to what the treatment would cost if it is one day commercially available," they say in an emailed statement to U.S. News.

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For the four women, though, and the doctors who performed the procedure, "It was very rewarding," Atala says. "With these conditions that they had, it's not just the anatomical defect, it's also the overall emotional well-being for them – for any patient – who has this type of challenge."

The new procedure he and his team used could offer some advantages over current treatments for MRHK, which call for dilating existing tissue or using reconstructive surgery to create completely new vaginal tissue, at times by using skin grafts of tissue that lines the abdominal cavity.

This method can be rife with problems: The so-called vaginal “substitutes” frequently lack a muscle layer, which can lead to a contracting or narrowing of the vagina. As many as 75 percent of pediatric patients suffer complications from the procedure, most often due to narrowing or contracting.

The new procedure has been in the works since the early 1990s, when Atala and his team first explored lab-built vaginas in rabbits and mice.