The increase in women migrants occurs as beefed-up border security has funneled migrants through one of the world's most forbidding deserts, and as smugglers adopt increasingly violent tactics.
Some women cross with their children. Others leave them behind with relatives. Pregnant women, like Maria Perez, the 18-year-old who gave birth this week, walk for days through the desert in the hope that their children will have a better life as US citizens.
Rape has become so prevalent that many women take birth control pills or shots before setting out to ensure they won't get pregnant. Some consider rape ''the price you pay for crossing the border," said Teresa Rodriguez, regional director of the UN Development Fund for Women.
If caught by the US Border Patrol, women are often deported to Mexico's violent border towns in the middle of the night, despite a 1996 agreement between the two countries that promised women and children would only be returned in daylight hours, according to directors of migrant shelters along the 2,000-mile border.
Worldwide, nearly half of the estimated 180 million migrants are women, according to a report released in February by the Economic Commission for Latin America and the Caribbean.
A study released last week by US and Mexican migration experts, partly funded by the Mexican government, found that nearly half of all Mexican migrants living in the United States are women.
The female migrants are getting younger. Of migrants under 18 deported to Mexico, females accounted for only 2 percent in 1994, when the United States started cracking down at the border. Since 2002, they have made up nearly a third each year, said Blanca Villasenor, who recently published a book on Mexico's female migrants.
''It's very significant because it shows the country is losing its potential -- its youth, its reproductive force," said Villasenor, who runs a youth shelter in Mexicali on the California border.
Central American women face even more danger because they must first cross Mexico, where gangs and even immigration officials have attacked women, said Jesus Aguilar, a migrant rights activist in El Salvador.
