Yennefer, like most sorceresses, is sterile and secretly sought a way of restoring her fertility. In the case of sorceresses, infertility comes as a consequence of magic, which has damaging effects on their reproductive system.

Can Yennefer get pregnant?

It was, perhaps, one of the more bizarre plot lines of the series, though we can't blame the showrunners, it's pulled directly from the novels. In fact, in the novels (and in the show) both Yennefer and Geralt are incapable of having biological children.

Is Geralt of Rivia infertile?

Geralt of Rivia, may have found a way to reverse his sterility, albeit inadvertently. It's a known fact that a witcher's mutations render them unable to reproduce. However, the famous white wolf, Geralt of Rivia, may have found a way to reverse his sterility, albeit inadvertently.