What pregnant woman hasn't heard the line, "You're carrying low. You must be having a boy." Or: "If you have morning sickness all day, it's definitely a girl."
Even stranger myths for predicting the baby's sex exist. One suggests that mommies-to-be hang their wedding ring from a strand of the father's hair over their belly. Another advises them to mix their urine with Drano; the color is supposedly a clue about the baby's sex.
Pregnancy Week by Week
If you are newly pregnant, or trying to conceive, you have many questions about what to expect. How will your body change? What's happening inside you? Here's what to expect week by week.
Now that medical technology makes it possible to determine an unborn baby's sex with almost total certainty, why do these old wives' tales persist?
The Internet is at least partly to blame for the ongoing pregnancy rumor mill. Social media sites like Facebook and Twitter have turned anyone with a keyboard into a pregnancy "expert." Myths fly through cyberspace, bouncing from one email inbox to another at warp speed.
People reading those random comments can wrongly take them for medical facts. "Sometimes people take what's said online at higher value than what their physician says," says Sharon Mass, MD, a practicing ob/gyn in Morristown, N.J. and clinical assistant professor at the University of Medicine & Dentistry of New Jersey.
Believe It or Not?
Even though most wives' tales about guessing the baby's sex are harmless, "My medical caution to my patients is: Please make sure you know the source of what you're paying attention to or sharing," Mass says.
New moms -- especially those who are pregnant for the first time -- can be especially susceptible to pregnancy rumors, says Eileen Beard, CNM, FNP, MS, senior practice advisor for the American College of Nurse-Midwives. "You're so concerned about doing the right thing and getting all the information. I think it makes you very vulnerable in a way. Even people who wouldn't normally believe myths are more likely to."
Another reason why sex prediction myths persist is that sometimes they can appear to be right. When you're looking at 50/50 odds, predictions are bound to come true half the time. And surprisingly, at least a couple of these methods do have some evidence to back them up.
Here's what experts told WebMD about a few of the most rampant baby sex prediction rumors.