I’ve never thought Regina and Leopold ever shared a bed. He wasn’t interested in her that way, and he wasn’t the type of man who would make his wife sleep with him out of duty, though they had no romantic interest in each other. He had no desire to have more children. He cherished Snow so much because she was a result of the love he shared with Eva. A child with Regina would not have fulfilled him in the same way, so I doubt he was at all interested in making babies with her.
As for the question of Regina potentially being infertile, I could see Cora doing that, so that her daughter was never distracted by developing love for anyone.
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