A Baby’s Sex Can Impact Mom’s Immunity During Pregnancy, Study Finds

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It wasn't that long ago that a woman would go her entire pregnancy without knowing the sex of her baby. Advances in medicine have allowed us not only to know the sex of the fetus before birth, but also better understand how the sex might affect a pregnancy. There have always been "old wives' tales" about what carrying a boy or girl feels like, but now researchers have found pretty interesting evidence. New research shows that a baby's sex impacts mom's immunity during pregnancy — and scientists are only just beginning to figure out what this means.

You've probably heard adages like, if you're craving sweets you're having a girl, or if you're "carrying low" it means you'll have a boy. These old wives' tales — and plenty more — have been around forever. While some of them make for fun baby shower games, they aren't based in hard evidence. But some of them may actually have been on to something. One such prediction says that women will have worse morning sickness if they're carrying a girl, and about 10 years ago, scientists did find a link between female fetuses and hyperemesis gravidarum — a severe form of morning sickness.

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The latest research, completed at The Ohio State University Wexner Medical Center, observed the pregnancies of 80 women and looked at whether they had different levels of cytokines in their blood depending on the sex of the fetus they were carrying. Cytokines are a type of immune marker that can give scientists clues about how a person's immune system is working, especially when it comes to inflammation.

Researchers found that the women in the study didn't necessarily have more cytokines in their blood based on the sex of the fetus they were carrying — but those who were pregnant with female fetuses seemed to be producing more of a certain type of cytokine. Women who were pregnant with female fetuses produced more pro-inflammatory cytokines when their bodies were exposed to bacteria than the women who were carrying male fetuses.

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In other words, the women who were carrying female fetuses demonstrated heightened immune response during their pregnancies. While we want our immune systems to get into gear to help us fend off bacteria that can make us sick, if our immune system goes into overdrive, all that inflammation can actually make us feel worse. Autoimmune diseases, for example, occur when the body's immune system goes haywire and starts attacking the body's own cells, not realizing that they aren't a threat.

While carrying a female fetus isn't an autoimmune disease, researchers do wonder if the heightened levels of inflammation — even if they're minor and temporary — might explain why many women report having worse morning sickness while pregnant with their daughters than sons, or may feel like health conditions they had pre-pregnancy, such as asthma, got worse when they were pregnant with a girl rather than a boy.

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More research is needed, of course, to figure out what this could mean for women, especially those who have autoimmune disease and would like to get pregnant. But it's pretty neat that after all these years of our mothers and grandmothers passing down those superstitions, it could turn out that our ancestors might have been on to something.