Shadow Heir by Richelle Mead

 The result of Eugenie's wild escapades with Kiyo turns out to be twins, who are prophesied to rule both the faerie and human realms as the Storm King's heirs. Those who are opposed to this are hoping to kill her before the twins are born, which makes traveling back and forth between the worlds so she can make her obstetrician appointments a bit dangerous. After one too many attempts, she decides she must go into secret exile until she delivers, so Roland finds her a secret hiding place with a shaman he knows in Huntsville, Alabama. The shaman has a nephew with whom I'm sure Eugenie would develop a love interest, were this series to continue further, but Mead says it's the last one, so we're spared that bout of mad, passionate, graphic sex anyway.

The twins decide to come early, so Eugenie undergoes an emergency C-Section, and they both turn out to be healthy, but require some time in NICU before she can take them "home". Just as she's about ready to do that Roland visits with news that her kingdom and many of the others in the Otherworld are under a spell keeping them in unnatural winter (shades of Narnia!), likely cast by the queen of the Yew Land, Lania?? She decides to return immediately to see if she can save her land, and bands together with Dorian, Kiyo, Jasmine and some of her underlings on a quest to break the White Witch's faerie queen's spell. Since Kiyo tried to kill her and their unborn children, she's not happy about him coming along, but he is Maiwenne's contribution to the cause, so she can't argue about it too much. Her demonic familiar, Volusian, once lived in the Yew Land, and he seems to have unfinished business there which trumps his hatred of Eugenie, so he turns out to be quite helpful in the quest.

The saga does mostly wrap up in this novel, but not so tightly that Mead couldn't bring the series back to life if it were necessary, or inspiration struck. All of the same potential for conflict with other faerie rulers and personal drama still remains, the only thing that's settled - somewhat - is the Storm King's progeny's prophecy.