A mysterious cluster of severe birth defects in rural Washington state is confounding health experts, who say they can find no cause, even as reports of new cases continue to climb. Federal and state officials won’t say how many women in a three-county area near Yakima, Wash., have had babies with anencephaly, a heart-breaking condition in which they’re born missing parts of the brain or skull. And they admit they haven't interviewed any of the women in question, or told the mothers there's a potentially widespread problem. But as of January 2013, officials with the Washington state health department and...