Women who are stressed and anxious during pregnancy tend to have children who with more advanced mental and motor development by age 2, U.S. researchers say.

A study of 137 healthy women with low-risk, typical pregnancies produced the surprising result, say researchers from Johns Hopkins University and the National Institute of Child Development.

"While these findings may seem counterintuitive, chemicals that are produced by stress have a well-known influence on organ growth and development," said lead author Janet DiPietro.

"Mild to moderate stress has been proposed to be important to successful adaptation to the environment after birth and necessary for optimal brain development," DiPietro said.

While it's possible the findings might have been different if the study had examined pregnant women undergoing severe turmoil, DiPietro said women with typical pregnancies should "stop worrying about worrying."

The study, which examined women between 24-32 weeks of pregnancy and six weeks and two years after giving birth, was reported in the journal Child Development.

Copyright 2006 by United Press International