I was never good at strolling.

If I had a destination, I walked quickly. Not because I wanted exercise, mind you, but because it felt natural.

That all changed with my first pregnancy. The nonpregnant me bolted across a street with five seconds left on the crossing signal. The uber-pregnant me much preferred a full 30-second allotment. Anything less and I waited for the next traffic cycle.

This change of pace was entirely out of my control. As I neared my due date, my once-brisk stride was shorter, my stance wider, my torso tilted farther backward.

I had morphed into a waddler! And I could only waddle so fast.

Now, at 28-weeks pregnant with my second child, I'm beginning to waddle again. I'm thrilled to be expecting, but I'm already missing my normal speed.

Obstetricians tell us that there's a good explanation for why pregnancy changes our gaits.

"There are a lot of joints in the pelvis. Those are going to loosen as the pregnancy goes on, which is probably how the body adapts to allow a fairly good-sized baby to fit through," explains Dr. Daniela Carusi, director of both general gynecology and surgical obstetrics at Brigham and Women's Hospital in Boston. The loosening of the joints and the downward pressure from the growing belly actually cause the pelvis to get wider, she says. A wider pelvis means a wider stance.

That explains part of the waddle. The other part, according to Carusi, is caused by a shift in our center of balance. "As the belly gets bigger, which is the spot in the body which marks the center point, the weight moves forward and that makes the spine curve more inward," she says.

We pregnant women can't help but lean back.

I wondered what would happen if I attempted to trade comfort for more graceful motion, if it was even possible to force myself to return to something closer to my former stride.

Carusi warns that it wouldn't work. "You could reposition your legs, but it's hard to make your hips narrower," she says. "What you'd be doing is compensating for the change instead of overriding it."

"I don't think it makes sense to narrow the gait," agrees Stephanie Prendergast, a physical therapist at The Pelvic Health and Rehabilitation Center in Los Angeles. "Keeping the gait wider is safer for balance reasons."

Prendergast says we could consider making slight adjustments to the way we stand. "When they're standing still, many pregnant women will push their bellies out and lean backward," she explains. "But then your ligaments at the front of the hip are holding up your weight." If we don't lean back so far, she says, our gluteal muscles could take some of the weight and our hips would hurt less.

I tried to adjust my stride anyway, of course. Unsurprisingly, it felt terrible. When I straightened my back, my shoulders arched forward. When I narrowed my stance, my balance was all off. Other women have had similar experiences.

"I tried to walk with my feet closer together, but after a while that hurt more than changing my gait," says mother-to-be Keke Gibb, a science professor at Baker University in Baldwin City, Kan., who spoke with me on her due date. "It's most comfortable if you widen your stance a lot," she explains. "It feels like my thighs hate each other. I try not to let them touch while I do a really awkward sashay through the neighborhood. I use my whole body to swing one leg forward at a time."

There is no fighting the pregnant waddle.

I take some comfort in knowing that there's a small community of scientists investigating how this altered motion affects our lives. These researchers attach reflective stickers to a pregnant woman's body and then use special cameras to capture the 3-D movement of the stickers as she walks, stands up, or does other simple tasks that can become challenging late in pregnancy.

"When we look in our software, the women look like stick figures moving in 3-D, so we can capture different aspects of how they move, rotate, flex and extend," says Jean McCrory, a biomechanist at West Virginia University who studies gait and balance in pregnant women.

McCrory documented, for example, how pregnant women walk with pelvises tilted backward and feet spread wider apart. Others have shown how we rise from chairs more slowly, and with a greater attention to balance.

In a recent study, scientists at Hiroshima University studied the mechanics of movement as pregnant and nonpregnant women rose from a chair, picked up two stacked plates, turned to the right, and then walked away. The researchers showed that pregnant women flex their hips less while walking and lean back more while standing.

These findings will come as no surprise to obstetricians or anyone who has ever had a baby bump of her own. But studies like these might one day help scientists figure out how to make everyday tasks safer for pregnant women. McCrory, for example, wants to use her knowledge of pregnant motion to find ways to prevent pregnant women from falling — a worthy goal since over a quarter of pregnant women fall at some point.

I joined that statistic during my last pregnancy when I got overexcited about an old friend visiting. As she got out of her car, I momentarily forgot to waddle and leaped forward to hug her. My toe caught the sidewalk and I fell so slowly and awkwardly that she thought it was intentional — that I was trying to entertain her with some sad attempt at pregnant lady slapstick. The baby and I were fine.

So far I've managed to stay on my feet this pregnancy. For the moment, I also still have some of my prepregnancy speed. I know this because, like so many aspects of pregnancy, people comment on it. Last week, as I strode past two men on my way to work, I overheard one say, "Whoa! Look at how fast she walks — for a pregnant lady."

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