NEW YORK (CBSNewYork) -- Every pregnant woman has heard theories about the sex of her baby -- what she craves or how she's carrying means either a boy or a girl.
Now, a new study says there's some science to some of this.
As CBS2's Dr. Max Gomez explained, the sex of the baby could affect a woman's immune system.
Pregnant with her second child, Melissa Fox found many of the old wives tales about the differences between carrying a girl and a boy were true.
She craved different foods with her babies and she carried them differently, but what she didn't expect was the allergies she thought she had outgrown were back with a vengeance while pregnant with her daughter.
"When I was pregnant with Ren, that's when I noticed they were like, seemed like they were kicking up and flaring up again where I was having to take something on a daily basis," Fox said.
A new study at the Ohio State University Wexner Medical Center shows that it might be more than allergy season that caused Melissa's symptoms.
Researcher Amanda Mitchell followed 80 women through pregnancy and exposed their immune cells to bacteria in the lab.
"What the findings suggest is that women carrying a girl exhibit greater inflammatory responses when faced with some sort of immune challenge," Amanda Mitchell explained.
That inflammatory response includes proteins called cytokines, which the body releases to fight off sickness.
It seems the immune cells of pregnant women carrying girls released more pro-inflammatory cytokines than those carrying boys.
"Too many of those cytokines or too much inflammation can really be unhelpful for our bodies functioning. It can create or contribute to symptoms like fatigue or achiness," Mitchell said.
Melissa took part in the study and said the results make a lot of sense based on her experience, but that suffering through her allergies was well worth it.
"Obviously I love both of my children. I'm glad that they're here. But, it was really interesting to me, just the differences that I experienced," she said.
It's not clear why baby girls seem to spike mom's immune response, and whether this reaction might also flare chronic illnesses, will be the subject of additional research.
Knowing whether you're having a boy or girl could help doctors with treatment recommendations for pregnant women.
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