I don't think it was very clear if that was a side effect of the genetic bomb, or if it was something else. I may have been a little distracted by the thought that they were making Looms canon, but I would love it if that's where they go with this.
Edit: It might just be a coincidence, but I just realised there may be another link to the Looms. In her Cameo, Jodie's Doctor says there's a "great big time Schism on it's way". That article on the Looms? "devices used by the Great Houses of the Time Lords to perpetuate their race after the Great Schism."
It's probably not going to happen, but I can dream.
Going back over the scene, it's confusing. The Rani says it was the genetic bomb, but earlier she said she'd flipped her DNA to avoid it. She says their species as a whole is infertile ("a biological dead end"), which sounds like she's talking about more than just the two of them. If the genetic bomb was a slow, lingering extinction rather than an instant death, why did she only have a split second to avoid it? Maybe that means that others survived the genetic bomb as well, but the Doctor already knew about the infertility despite not knowing about other survivors. Add to that the Rani's disgust at Mrs Floods comments last week about the new Rani being her child, and the whole thing feels like two different ideas squashed together and not quite fitting.