Because "smart" is such a vague term, I thought I would break down the brain-boosting benefits of motherhood into the five most likely "smart" attributes: perception, efficiency, resiliency, motivation, and emotional intelligence. All of these categories have been supported by many animal studies as well as some human studies designed to show how mothers have an edge.
The category of perception deals mainly with the five senses. A study I found very interesting showed that pregnant women had sharper "visual acuity" than women who weren't expecting. This study certainly didn't imply that expectant women suddenly had 20/20 vision, but they were more aware of detail that they may have overlooked prior to pregnancy. Other studies have also showed that pregnant women have an enhanced sense of smell which researchers believe serves as a way to protect the unborn baby from foods that are potentially harmful.
Furthermore findings show that expectant women can experience a boost in motivation, fearlessness, and the ability to multitask and cope with more stress. Exciting new research also suggests that oxytocin — a hormone important to labor and breastfeeding — improves a moms' capacity for learning and memory.
Emotional intelligence is the most definitive category in which mothers benefit. This brain boost for moms acts as the ability to see the world through someone else's eyes. In most of life's relationships, if you don't agree with a person you can just walk away, but you can't walk away from your child. At least, not if you want to be a good parent. Instead, you've got to stretch your mind to understand their point of view. In no way did any of these studies suggest that women who weren't pregnant were lacking in any of the five researched areas but instead they simply confirmed that the changes women were noticing in themselves were in-fact valid and accurate.