Pregnant women get lots of advice: eat healthy, don't drink, rest. Soon, "maintain your mood" may be added to that list.

A new study examining how mom's mood affects the baby during pregnancy and beyond is getting lots of attention--and it hasn't even been published yet. It is scheduled for publication in December in the journal "Psychological Science."

Researchers at the University of California-Irvine studied mothers and their babies during and after pregnancy. The team, headed by Professor Carl Sandman, checked more than 200 moms for signs of depression and checked the babies to see how well they were developing. The team found that what mattered most to babies before and after birth was consistency, and not so much the mood itself. According to the researchers, changing conditions, going from not depressed to depressed or the other way around, slowed babies' development.

These findings speak to something called "prenatal programming," that the fetus is being prepared to adapt for the conditions it will find once born.

For example, if a pregnant woman experiences a famine, the fetus prepares for scarce food sources after birth.

Neill Epperson directs the Penn Center for Women's Behavioral Wellness.

She says Dr. Sandman's research is already getting lots of attention and will attract controversy once published. "Multiple studies show that post-natal depression has adverse effects on many aspects of child behavior and cognition," said Epperson. "Sandman's finding is surprising with respect to the data that we have but it is not surprising with respect to this concept of prenatal programming."

Epperson says she respects Dr. Sandman, his team and their contributions to understanding the impact of mothers' moods on fetal development.  But she worries that women who are depressed during pregnancy might interpret this latest study to mean that they shouldn't receive treatment after the baby is born.  She says that would be a bad choice as both mom and baby will benefit long term when depression is treated.  Research has shown that when mothers are depressed, children often develop behavioral and school problems.

Epperson says women who experience depression during pregnancy should be treated as soon as possible.