Brain

What's going on: Think you're losing your mind? You may be right -- MRI scans of pregnant women have shown that brain size actually shrinks in the third trimester (but plumps back up a few months after birth). Other research has found that concentration, short-term memory, and learning ability are significantly impaired in late pregnancy. No one knows just what turns expectant moms' minds to mush, but lack of sleep during this fairly uncomfortable period may contribute to this mental fogginess.

What to do about it: Update your "to-do" list daily and leave reminders in hard-to-overlook spots. Most importantly, though, cut yourself some slack. After all, pregnancy has a way of reminding you that there's more at stake than picking up your dry cleaning on time or beating your husband at Trivial Pursuit — like growing, giving birth to, and being responsible for a brand-new life.

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