Last April, researchers in Britain reported that women who ate more breakfast cereal were more likely to conceive sons. Today, a team of scientists cried "hooey."
"In statistical terms, it's a false positive," said Stanley Young, a co-author of a paper in Proceedings of the Royal Society B and a statistician trained in genetics with the National Institute of Statistical Sciences Research, Triangle Park, N.C.
Young's team had several reasons to question the cereal-eating moms study, but one major red flag was that the researchers asked too many questions in their 133-option diet questionnaire. Put enough variables into a study, Young said, and meaningless statistical flukes can arise.
"If you just ran these studies over and over and over again, you'd always find a food that predicted boys and girls, but it would be a different food every time," said Young. "The gender of humans is determined by the x, y chromosomes of the sperm -- the woman has nothing to do with it."
Modern day pregnancy myths abound among patients with high school sex education classes and some Google researching under their belt.
"The reason we picked up the paper is that there are a lot of claims that appear in the newspapers that just don't look right," said Young.
Doctors said most of these myths, whether they're adapted from news or thought up at home, fall into distinct categories: what people want and what people fear.
"Then there are all the myths of how you can ensure that you have a boy or ensure that you have a girl," she said.
Dr. Richard J. Paulson, chief of Reproductive Endocrinology and Infertility at the Keck School of Medicine at the University of Southern California in Los Angeles, said he hears the same myths about gender selection year after year.
Paulson said many of the misconceptions about controlling a baby's sex come from a single book: the late Dr. Landrum Shettles' "How to Choose the Sex of Your Baby."
The book has sold more than 1.5 million copies and is the first source for the idea that male sperm are sprinters and female sperm are marathon runners.
"I'm not even sure what research this was based on, but because he was a doctor, people believed it," Paulson said.
Paulson has never seen research that could confirm this idea, or research proving that the methods in Shettles' book work, but he has seen plenty of patients who tried to change the odds for having a boy or a girl.
By the Shettles method, couples wanting a boy should try to conceive right after the woman has ovulated, presumably to give the faster, yet short-lived male sperm a better chance to get to the egg.
If a couple wants a girl, the Shettles method says to try to conceive a few days before the woman ovulates to let the male sperm die off and give the so-called heartier, yet slower, female sperm a chance to make it to the egg.
"This thing has absolutely percolated into the population and everyone believes it," said Paulson.
"Guess what? It doesn't work," he said. "There's never been one shred of evidence that it works."