Narrator: This is Science Today. Sylvia Guendelman, a public health expert at the University of California, Berkeley, found that Mexican-born women living in the U.S. tend to have healthy babies of normal birth weight, in spite of poverty and little access to prenatal care. What's more, birth weight goes down with the next generation, born in the United States.

Guendelman: Mexican-American women already born in the U.S. have an increasing rate of low birth weight. It moves up from 3.9 to 6.1 percent.

Narrator: The reason, says Guendelman, is the Mexican-born women eat a healthy diet, and most don't smoke or drink.

Guendelman: I do think that what we're learning in public health is that behavior such as smoking or drinking or eating an unhealthy diet might have a stronger influence or impact on birth outcomes than prenatal care per se.

Narrator: For Science Today, I'm Steve Tokar.