Is the nesting instinct a real thing?

My house was never more organized than during the third trimester of my first pregnancy. The fact that I worked from home made it easy to clean out a drawer or closet whenever the urge struck—which was often. Turns out I'm not alone in my desire to clean and tidy before baby arrives.

In fact, a pregnant woman's compulsion to get organized is so commonplace that there is a phrase for it: the nesting instinct. "My urge to organize was mild at first," says Leanne Grechulk, from Burlington, ON. Then, around the seven-month mark, she felt a sudden sense of urgency. "I was hit with a need to give stuff away. At one point I was donating things almost daily. And at the end of each day, my floors had to be vacuumed and everything had to be put away."

Could this deep desire of pregnant women to clean and purge be frivolous, or is there something stronger driving it? Turns out that the nesting instinct is actually an adaptive behaviour stemming from our evolutionary past. Researchers at McMaster University in Hamilton, ON, found that the nesting instinct comes from the desire to provide a safe environment for the new baby, something both animals and humans experience. "It's about space preparation," says Mel Rutherford, a professor in the department of psychology, neuroscience and behaviour at McMaster. "It stems from the desire to get the space ready, remove any potential dangers, and be physically prepared when the baby arrives."

Time to nest
Nesting behaviour is typically seen in the third trimester. This is usually when "mommy-brain" kicks in. "There are measurable changes in short-term memory during the third trimester," says Rutherford. An expectant mom's priorities change, her efforts going more toward physical preparation rather than cognitive development.

This may be one of the reasons why women in their third trimester experience bursts of cleaning energy, despite being more tired. "Toward the end of their pregnancy, women will feel like they're dragging and doing less; then they'll go home and clean the garage," says Rutherford.

Tidy with care
"Our view is that nesting is a natural and adaptive behaviour," says Rutherford. "There's no reason to find excessive cleaning and organizing problematic, except in really specific cases." Nevertheless, you do need to listen to your body. If you're feeling worn out, it's time to stop. Contact your doctor if you experience excessive fatigue, pain or swelling, vaginal bleeding, or anything else that makes you feel uncomfortable.

When using cleaning products, experts recommend doing so in a well-ventilated area. You may want to pass on cleaning the oven, which is a tight space. Also, moms-to-be should ask for help when moving heavy furniture.

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