For Father’s Day, Mayhem and I gave & a book called “The Expectant Father.” This book, it turns out, says things that no book written for expectant mothers would ever dare to put in print. For example, it claims that the brains of pregnant women shrink 3 to 5 percent during pregnancy.

“But does it grow back afterward?” & asked.

The book offered no insight on this.

I don’t feel any dumber (although maybe my episodic lightheadedness is more than just figurative). But I have had trouble finding enough words that rhyme with “pregnant” to make a decent limerick. “Indignant” is the best I can do. Maybe the 3 to 5 percent of my brain that’s currently out to lunch would help, in the event that it ever does come back.

In any event, this is life at six months pregnant.

Mayhem is happily treading amniotic fluid, nudging me every so often to remind me she’s there. Baby shower plans are underway. The baby registry is set up (at Amazon and BuyBuyBaby). I’m back on a regular gymgoing schedule, jogging daily on the elliptical while scrupulously keeping my pulse under 150. I’ve been cleaning out my freezer and pantry, saving oodles at Whole Foods by using up the food we’ve already got (and then using the saved oodles to buy maternity clothes). And I have plenty of energy, except when I don’t.

I’ve concluded that these periodic dips in my energy level correlate to Mayhem’s growth spurts. It’ll start out with a small, very local mini-cramp halfway between my navel and my hip, usually on the right side, kind of like a rubber band stretching. Often, a day or two later, I’ll notice a similar cramp on the opposite side, or maybe some pressure where I hadn’t noticed it before. And then I’ll wake up the next morning and my Pregnant Tummeh will have leveled up.

The latest growth spurt, precisely at 25 weeks, may have accomplished something I’ve been waiting to see for months. For as long as I’ve been paying attention, I noticed something about other pregnant women’s baby bumps. Whether they’re maternity-wear models or random women on the Metro, my gravid compatriots all seem to have the most wondrous bellies: firm, smooth hemispheres, neatly and proudly protruding, often crowned at the equator with an adorably everted navel.

My own Pregnant Tummeh is a different story. Ten or so years ago, I used to be a Fat Person — a plus-sized mouse potato with a distaste for exercise and a love for rich food and good booze. In the intervening decade, I discovered the gym, the benefits of dieting, and the delightful influence of people with hobbies other than sitting in front of a computer. By the time & and I got married, in October of 2009, I looked like this. But no matter how much weight I lost, I still wore the loose-fitting skin of a Formerly Fat Person. And no matter how quickly Mayhem grew, it seemed that my Pregnant Tummeh was still too big on her.

My bump looked sort of like this, only without the belt. (Or the continents.)

Until yesterday.

I felt the little cramplet in my right side. The pressure. An increase in Mayhem’s fidgeting. Another faint stabby cramp on the left. And this morning, for the first time, it looks as though my vestigial “waist” — an equatorial dent which spanned my Pregnant Tummeh and made it look like two spare tires whenever I sat down — has finally evened out.

It’s not completely globe-smooth, but that’s fine. There are three months left in this pregnancy, and more room to grow now means (hopefully) fewer stretch marks later. I’m just flattered and gratified to see Mayhem leaving her impression on my waistline.

From the inside out.