Lately, I've seriously considered wearing a sandwich board sign. It would say:

Thanks for pointing out that I am obviously pregnant.
I'm due Feb. 13.
It's a girl.
No, there's just one baby in there.
Yes, I'm still teaching fitness classes; and no, exercising won't harm the baby
.

I steeled myself for these questions, having been through them with my now 2-year-old son. Since many of the students I teach at my company, Philly Dance Fitness, saw me bopping around until a month before he was born, I thought I wouldn't have to respond to as many inquiries about the merits of exercising while pregnant. But there have been new students since then — so, to those of you who are curious and pregnant women alike, here's my quick guide to what we preggos can and can't do when it comes to fitness.

(These guidelines will hold true for most pregnancies without complications, but everybody is different and pregnant women should always consult with their doctors to confirm what exercise routines are best for their circumstances.)

Start Exercising

Pregnant women can — and should — exercise on a weekly basis. Aside from possibly helping you feel better during the pregnancy, staying active throughout can also make returning to pre-baby shape so much easier. OBs will usually say that it's safe to continue doing whatever exercise routines you were doing before pregnancy, with modifications as the baby grows. In other words, if you're not a runner already, it's maybe not the best idea to start training for a marathon after you get pregnant. But this "continuation" policy can also create a perfect excuse for non-exercisers to remain sedentary throughout pregnancy or even for active women to slack off a bit. You can try new forms of exercise, increase your workout frequency and even challenge yourself to go for a higher impact program while pregnant – within reason. What I mean by that is if you're going to try something new, go for flexible cardio or strength programs. Zumba? Aquacize? Sure. Sculpt, spinning, boot camp, great. However, it's worth waiting those nine months before you pick up an activity that would be hard to modify as you get bigger, like say, pole dancing, or one that could present blunt impact to your midsection, like dodgeball.

Lift Weights

Remember all that uproar in the spring about the pregnant woman who continued her CrossFit weight-training regimen up until giving birth? According to a number of articles, she set several personal records, including dead-lifting more than 200 pounds. This is obviously beyond extreme, but there's no reason to stop lifting while pregnant.

My doctors advised lifting no heavier than 10-15 pound dumbbells per hand.  You can still do a lot to keep your arms and back toned with lighter weights or bands, though you may need to focus on endurance by increasing reps rather than resistance. Make a point of breathing normally — none of that forceful exhaling that lifters sometimes do, which can potentially decrease oxygen flow to the fetus.

If you're already in the midst of a program to build muscle, this is where you definitely need your doctor to weigh in (pun so intended). No matter how fit you are, you can't stop the skin and joints from becoming more relaxed to create room for the growing fetus. That means even practiced lifters will become more prone to injury.

You may also have to remind yourself to think more about posture when lifting anything heavy in the later stages of pregnancy. It's easy to forget because you get used to compensating for the extra weight in front of you.

Choose Your Impact

Another common myth is that pregnant women should "take it easy" when working out. The only reason to tone it down is if your body tells you to. And believe me, it will – possibly at the beginning if you're nauseated non-stop; for sure toward the end when all that extra weight seems to just bear down on your frame (or your bladder, or your pelvis…) Gaining 20 to 50 pounds in a few short months is no joke. But in those times that you're lucky enough to feel just fine, why not go hard?

And yes, jumping, deep squats, lunges and the like are all OK as long as you feel OK doing them. When I was pregnant with my son, my worried mother made sure to mention – several times – the risk of placental abruption, which is when the placenta partly or completely detaches from the wall of the uterus. Sometimes it just happens, other times it's caused by severe trauma to the abdomen, say from being in a car accident or falling. There's no evidence to indicate that jumping or other types of exercise leads to this condition. The uterus is an amazingly strong muscle and that baby is cushioned by plenty of fluid and tissue. Worried loved ones will understandably point out that you could have a greater risk of falling while jumping, or at least face a greater impact if you did fall. But you could also be hit by a car while crossing the street, and that's no reason to sit on your couch eating chocolate all day.

Head Above the Belt

While I've been hammering the message that pregnant women should workout just like they always did, there are two positions we have to avoid. Medical experts recommend not raising your hips above your head at all while pregnant – which is really annoying if you love doing bridges in yoga, or in my case, you teach striptease aerobics. They'll also tell you not to do exercises lying down because the extra weight of the baby plus accoutrements can restrict the vena cava, a major vein that carries blood from the lower body back to the heart. But when exactly is the uterus big enough to cause this problem? Who knows. The American College of Sports Medicine recommends avoiding prone positions after the first trimester — but some newer research contends that this guideline is overly cautious for most women.  So, if you're going to push the recommendations here, force yourself to break your normal reps into small chunks, and shift to a seated or standing position between sets to make sure you're getting enough blood flow. Better yet, stake out an inclined bench.

Fans of yoga and Pilates, which often involve quite a few floor exercises, may be particularly frustrated by this rule. With the help of Google or a good instructor, you can find ways to modify many prone exercises into standing positions.

Aside from these two restrictions, most standing or sitting positions are fair game, as well as horizontal positions like planks. Yes, your belly may eventually scrape the ground, but that's no excuse for skipping your push-ups.

As with anything while pregnant, be extra mindful of whatever you do, gradually pull back as your body dictates, and you'll be fine.

Deborah Hirsch, president of Philly Dance Fitness, is a certified fitness instructor, personal trainer and choreographer. She challenges you to a dance-off with the pregnant lady. Find her classes at phillydancefitness.com or email her at info@phillydancefitness.com.