When I was in my third trimester of pregnancy, I walked out of the door one night with my dog...and without my keys or cellphone.

Luckily, my neighbors were home and happy to help, so the situation ended well. The only injury was to my sense of myself as a competent, functional adult. Was I suffering from the dreaded "baby brain"? As a new mom, would I start to forget important commitments or stare foggy headed at my computer as the right words evaded me?

I'm sure I'm far from the only expectant mother who has worried about this. Well-meaning relatives and countless blog posts warn pregnant women about a fall off in concentration and memory due to the hormonal surges involved in becoming mothers.

Here's the good news--according to science "baby brain" does exist, but it's not the hazy-headed incompetence that professional mothers fear.

What happens in your brain when you're expecting

Given the gargantuan changes in every other part of your body when you're pregnant, it would be a surprise if your brain wasn't also affected. And a growing body of research confirms that women's brains do change significantly in preparation for motherhood. In short, pregnant women seem to be more prone to anxiety (so that they'll worry about their babies, keeping them alive) and bonding (for obvious reasons). They also get better at identifying others' emotions.

"Even before the baby is born, certain parts of the brain show a structural increase as well as greater function," reports a recent Wall Street Journal write-up of the latest research. "This growth urges new mothers to bond with their babies, take care of them, and think about them constantly."

"All those urges to nurture can result in anxiety," adds the article.

What baby brain is not

Your brain may be pushing you to become baby-obsessed as your belly swells, but that doesn't mean it's simultaneously forgetting how to manage everything else in your life. In short, baby brain doesn't make you forgetful and dumb. Which makes sense from an evolutionary perspective--how could it be an advantage to become less competent after you reproduced?

In one recent study, "researchers at Brigham Young University gave cognitive and neuropsychological tests to 21 women in their third trimester of pregnancy and then tested them again six months after they gave birth. They administered the same tests at similar intervals to 21 women who had never been pregnant. They found no differences between the groups no matter when they were tested, including before and after giving birth," reports Scientific American, which continues:

These findings mesh with those from a 2003 study, which found that pregnant women did not score differently from nonpregnant women on tests of verbal memory, divided attention, and focused attention.

In fact, the brain changes associated with motherhood might just boost your memory. The science is still inconclusive, but studies on rodents show having babies makes them better able to find and remember food sources. "We can extrapolate there is evidence to suggest that multiple pregnancies enhance memory," Pilyoung Kim, director of the Family & Child Neuroscience Lab at the University of Denver, told the Wall Street Journal.

She goes on to sum up the state of the research on the subject in a way that can only reassure nervous moms-to-be: "We see this amazing plasticity in the brain during the early months of parenting that leads to mostly positive growth. So I cannot help thinking that the Mommy Brain is ultimately a good thing," Kim says.