It was just a nosebleed, caused by desert air. Or was it?

The night the nosebleed started, Zina Martinez, seven months pregnant with her second child, was sitting in the living room of her Las Vegas home, eating a bowl of ice cream.Martinez, 22, was used to nosebleeds. She’d had them nearly every day since she was 10, an annoying occurrence doctors repeatedly dismissed as insignificant — a probable result of the bone-dry desert air.This one was different.When Martinez pinched her nose closed to stop what was usually little more than a trick