Gibbon's Decline and Fall by Sheri S. Tepper
From the author of Grass and Shadow's End, an astonishing science fiction novel featuring a group of women racing to avert apocalypse at the turn of the millennium.
Fast forward to the year 2000: a ruthless politician is amassing a terrifying, fanatic power base; the suicide rate has gone through the roof... and the global birthrate has plummeted to near zero. Something evil is threatening the world. Of the seven extraordinary women forming the Decline and Fall Club, six remain. The seventh, Sophy, disappeared three years before, her dazzling, unearthly beauty undiminished. Her friends come to see that unlocking the secret of Sophy's disappearance will be the key to the survival of humanity.