For thousands of years, pregnancy has been considered one of life’s greatest mysteries. And as with most mysteries, humans have created all sorts of theories to explain the process, including a long list of “dos” and “don’ts” that get repeated over and over.

Three Pregnancy Myths That Researchers Say Are False

Advice is great. Advice from your mom, advice from a friend or from a distant relative. But new scientific research is proving a lot of old wives’ tales false. Here are three long-held beliefs and oft-repeated adages that just don’t measure up. Check them out, and then talk with your doctor to find out what’s right for you.

Myth 1: Pregnant Women Eat For Two

While it’s technically true that you’re eating to support two now, remember that only one is an adult. Pregnant women who are at a normal weight before pregnancy only need to add around 300 extra calories every day to properly nourish a developing baby. But even that much, at least during the first trimester, might not be necessary.

When you’re pregnant, your body becomes more efficient; it doesn’t waste as many calories, and actually learns how to absorb nutrients better. According to the Institutes of Health, most women won’t need to add any extra calories to their diet during the first 13 weeks of pregnancy. After that, and until you come to term, they recommend adding the 300 daily calories we mentioned before.

Myth 2: A Mother’s Stress Always Hurts Her Baby

The media usually emphasizes calm and rest for pregnant women, citing the adverse effects that anxiety can have during pregnancy. But the ideal of a “calm,” happy pregnancy might be a myth of its own; pregnancy can be super stressful, and it’s totally normal to experience anxiety and uncertainty about the future.

Now there’s evidence that low levels of stress might actually be good for babies. According to researchers at Emory University, recent findings suggest that “mild to moderate amounts of stress during pregnancy [may] help prepare the baby for later stressors, such as birth” and even “result[…] in healthier immune systems and better motor development.” The team is quick to point out that further studies are necessary before any conclusions can be drawn, but if it’s true that a moderate amount of anxiety actually helps a baby, we should be able to put our minds at ease a little. At least maybe we can stop stressing out about our stress.

But chronic, or traumatic, stress can affect a baby’s development. A growing body of research has found that women who survive earthquakes during the first trimester are more likely to deliver premature, underweight babies. And children born to women who were pregnant during a devastating Canadian ice storm in 1998 were found to demonstrate developmental delays, including lower IQ scores.

Prolonged anxiety, or feelings of depression, are another cause for concern. They’re also pretty normal: recent research has found that up to 20% of women suffer from anxiety or other mood disorders during pregnancy, according to Massachusetts General Hospital. But common doesn’t mean trivial. Depression and other psychological disorders are serious medical conditions, and pregnant women should speak with their doctors about any periods of persistent negativity, neutral emotions or anxiety.

Myth 3: Pregnant Women Shouldn’t Exercise

In a 2012 study, Dr. Melissa Hague found that many women actually stop exercising after learning that they’re pregnant, citing concerns that physical activity could hurt their babies. For some of these women, even a brisk walk was out of the question.

As it turns out, those concerns are unfounded. While you should always discuss physical activity with your doctor first, most pregnant women benefit greatly from regular exercise. Not just in the body; routine activity can help prepare your brain for the stresses of pregnancy and promote mental health.

If you worked out before pregnancy, it’s safe to continue your regimen, at least through the first trimester. After that, you may have to make some adjustments to your routine, but a medical professional should be able to give you good recommendations. If you weren’t active before, check with a doctor about gradually starting a regimen that will become regular.