False facts you believe about pregnancy

Pregnancy is a magical time of slowing down, growing a new life, and being subjected to unsolicited advice. Practically everyone you know will be banging down your door to tell you their secrets of predicting your baby's sex, or perpetuating yet another old wive's tale.

However, many of the pregnancy facts we believe don't hold up against the research. From exercise requirements to eating for two, there is a lot about pregnancy you might not understand.

Pregnancy lasts nine months

The length of pregnancy is one fact that I never questioned. We all know that pregnancy is made up of three-month trimesters, equalling nine months. You've probably planned it out perfectly. For example, if you're a teacher, maybe you'd love to have your maternity leave over the summer. However, planning your ideal pregnancy time just got a little trickier.

A study from the journal Human Reproduction found that the length of your pregnancy can actually vary by up to five weeks. Your due date is an educated guess based on the date of your last menstrual cycle. However, researchers found that only four percent of women studied delivered on their due date, and only 70 percent delivered within 10 days of the date.

Even obstetricians were caught off guard. "We were a bit surprised by this finding. We know that length of gestation varies among women, but some part of that variation has always been attributed to errors in the assignment of gestational age," Dr Anne Marie Jukic told BBC News. "Our measure of length of gestation does not include these sources of error, and yet there is still five weeks of variability. It's fascinating."

You can tell the baby's sex by the shape of your bump

I still remember the day I learned about this myth. I walked into work, still feeling slightly self-conscious about my changing pregnant body. One of my coworkers who prided herself on always predicting the baby's sex took a long look at me up and down. Then she asked me to turn around and yelled, "Yep, she's wider. It's a girl!"

Many believe that a higher, rounder bump means you're having a boy, and a lower, wider bump means it's a girl. However, it just doesn't work like that. "The baby's sex has absolutely nothing to do with the way a woman appears," Shari Brasner, M.D. assistant clinical professor of obstetrics, gynecology, and reproductive science at Mount Sinai School of Medicine in New York City told Women's Health. The way you carry your baby has more to do with your body type and genetics.

You can get a tummy tuck right away

By the end of your pregnancy, you're feeling exhausted and huge. Once that sweet baby makes her way into the world, you suddenly feel lighter and maybe a little more like yourself. That is however, until you look down. Your body is certainly not back to normal, and it's not supposed to be. However, some women have a hard time waiting to get their pre-baby bodies back. Plastic Surgeon Dr. Joshua Zuckerman has received requests from patients to perform an abdominoplasty (tummy tuck) during C-section surgery. If you're already going in, might as well get two-for-one, right? Not so much.

"While an abdominoplasty (tummy tuck) at the time of C-section may sound compelling and is technically feasible, it is the general consensus among plastic surgeons that it's not a very good idea," Dr. Zuckerman told me. "In pregnancy, everything stretches out fairly significantly including the skin, muscle, and the fascia of abdominal wall. When performing a tummy tuck, I'm obviously trying to get as tight, taut and smooth a result as possible." Because the skin is so stretched out from growing a baby, the plastic surgeon would not be able to be accurate with how tight to pull the skin. Not to mention the fact that a cesarean section is already major surgery as it is!

Cocoa butter will prevent stretch marks

We've all seen the cocoa butter lotion commercials with the beautiful pregnant woman gently massaging her perfectly smooth belly. No one looks forward to stretch marks, so we're all open to anything that can prevent them. According to the medical community though, stretch marks go much deeper than any lotion could address.

"The formation of stretch marks mostly has to do with a woman's collagen and how well her skin stretches," Dr. Yvonne Bohn told CBS News. While cocoa butter can moisturize your skin, it's not getting deep enough to affect the formation of stretch marks. Some people are even sensitive to cocoa butter and can experience redness and itching when using it.

You should monitor your heart rate while exercising

Exercising while you're pregnant is a great way to stay active, train your body for labor, and just feel like yourself again. However, the recommendations for how hard to workout have changed over time, and it can be hard to keep up. One such recommendation is that you should make sure your heartbeat never goes above 140 beats per minute, because that could mean you're exerting yourself too much. "This is still so pervasive in both the medical community and among pregnant women," Chrissy Carroll, MPH, RD told me. "However, as a personal trainer and USAT Level I Triathlon coach with a Masters in Public Health, I can tell you that the research and current guidelines do not support this recommendation."

Carroll told me that this recommendation has since been replaced, but that many pregnant women still worry about going too high. "The 140 beats per minute recommendation was actually removed from the ACOG guidelines back in 1994," explained Carroll. "Yet in 2010, a survey of almost 100 practicing physicians found that more than 60 percent still advised this limit." Rather than focusing on your heart rate, pay attention to how hard you're working during a workout. "Use the 'talk test,'" recommends Carroll. "If you are exercising at a rate where you can still speak in sentences, that's probably a good indicator that you're at the right intensity regardless of heart rate."

You shouldn't run when you're pregnant

Speaking of exercising during pregnancy, I have good news for the runners out there. If you were a runner before pregnancy, and your pregnancy has been uncomplicated, it's safe to say you can still be a pregnant runner.

Physicians don't recommend starting any new exercise program when you're pregnant, but you can keep doing what you doing before pregnancy. "A lot of what a woman can do during pregnancy depends on what she was able to do before pregnancy," Dr. Brasner told Women's Health. If you are used to your daily jog, keep doing it as long as it feels good.

You're eating for two now

"I know I shouldn't be eating this, but the baby wants chocolate cake!" We've all been there. You're tired, you can't have a glass of wine, and suddenly all of the food in your fridge sounds like a great idea. However, that tiny baby living inside of you certainly does not need an adult-sized portion every time you eat.

"In fact, a woman needs an extra 350 calories in the second trimester, 450 extra calories in the third trimester, and no additional calories in the first trimester," Andy De Santis, RD, MPH told me. "This amounts to an extra snack or two a day, certainly not eating for two."

Never skip a meal

If you happen to fall on the other side of the hunger spectrum, and nothing sounds good, don't sweat it. Many women deal with constant nausea during their pregnancies and have to be careful about what and when they eat. If you're not hungry, don't stress about eating three full meals every single day. "You should listen to your body," Dr. Alane Park told CBS News. "If you're really nauseous and have no appetite, it's okay to skip a meal."

Sushi is off-limits

Early into my first pregnancy, my husband and I were invited to a friend's birthday party at a sushi restaurant. "I can't go!" I immediately said. I knew I wouldn't be able to eat any of the food. However, many pregnant women safely eat sushi. "In the US, pregnant women may be advised to avoid sushi altogether [due to] the fear of dangerous microbes in raw fish," Intercultural Strategist and Coach Annalisa Nash Fernandez told me. "But Japanese women are encouraged to eat raw fish for the fatty acids that are considered fundamental for good neonatal nutrition."

Pregnant women are usually advised to steer clear of raw anything, for fear of contamination. "The overwhelming majority of food poisoning from seafood comes from raw mollusks that are rarely used in sushi, and deep dwelling fish like tuna in very cold water can't really get parasites at all," explained Fernandez. "So which is the myth?" If you're a sushi lover, talk with your doctor about which types are safe to try.

It's okay to skip the dentist

When you are pregnant, you have a lot on your plate. You may be sick, exhausted, and trying to keep track of all of your prenatal appointments. It's easy to let the dentist go for a while. However, many women believe that they are not able to visit the dentist while they are pregnant, and this is dangerous for both your health and the health of your baby.

"Poor oral health, most specifically gum disease, has been linked to both low-birth weight and preterm birth. Moreover, women are more susceptible to cavities during periods of hormonal fluctuation like during pregnancy and post-birth," Regional Dental Director for Jefferson Dental Care, Dr. Leslie Renee Townsend, told me. "Women who are pregnant often forgo dental cleanings, or worse, actually forgo receiving dental treatment, because they think they can't receive anesthesia or conduct x-rays, so they simply put off going. Unfortunately waiting to seek care can put mom and baby at risk."

If you are, or could be pregnant, keep your regular dental appointment and let the team know right away. During pregnancy, you may notice some oral changes like swelling or bleeding gums. Don't just tough it out. Your dentist can help.

Spicy foods can stimulate labor

When I was a week past my due date with my daughter, I tried everything, including spicy foods. I ordered nachos with extra jalapenos, poured hot sauce on my eggs, and even made an incredibly-complicated eggplant parmesan which promised to induce labor. Three hours later I sat in our kitchen covered in flour and marinara sauce, but still very much pregnant.

Unfortunately, the timing of labor is just not up to us. Dr. Brasner told Women's Health that having sex or eating certain foods is not proven to set off labor. Your doctor will discuss your options with you if you have gone past your due date.

You need to do your research

During your first pregnancy, there is so much information to take in. Learning about food aversions, stages of labor, and how to actually take care of a tiny human can quickly become overwhelming. While it is important to prepare, don't drive yourself crazy.

Author of Pregnancy from the Heart, Lauren Arboleda, recommends taking it easy on all of that prep. "Sign up for childbirth, breastfeeding, and infant CPR classes to have your own experience and increase your knowledge," she told me. "Despite what we're told, it is not always the best idea to search the internet for every video on labor and read every single article out there. This can lead to even more anxiety, confusion and stress. Don't try to know it all! It is humanly impossible…and when it comes to birth and motherhood, you need to follow your instincts." When you notice yourself starting to feel overwhelmed, close the laptop and maybe go take a nap.

You need to follow a certain diet

When I was pregnant, I became obsessive about my diet. I knew what foods to avoid, and I had been taking a prenatal vitamin months before trying to conceive. I was trying to do everything right, but kept coming across conflicting recommendations and then felt lost.

"We are constantly bombarded by all different sources telling us to eat this not that. But what really works? That can only be answered by YOU," explained Arboleda. "There is no 'one size fits all' diet for pregnancy, and what works for you may not work for me. Therefore, learn how to connect and listen to your body."

Arboleda recommends simply focusing on real food like good carbs, veggies, fruits, meats, dairy, and fats. "Your body needs a little bit of everything, and by everything I don't mean donuts, fries and cake," explained Arboleda. "Moderation is key!"

Heartburn equals hairy baby

I had terrible heartburn during both of my pregnancies and gave birth to babies with full heads of thick hair, so I have always believed that heartburn and hair are related. And it turns out, this pregnancy myth is actually true! A study from Johns Hopkins University found that this bit of pregnancy folklore holds up. It turns out the same hormones responsible for relaxing your esophageal sphincter, causing heartburn, are also responsible for fetal hair growth.

With all of the pregnancy myths and facts out there, always talk with your doctor about any question, big or small. You just never know which ones are actually true!