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A boy or a girl? Baby’s sex may influence mother’s immunity

Does the baby’s sex influence the mother’s immune system? A new study investigates the link between fetal sex and the mother’s immune response to illness.
[woman has an ultrasound]
New research suggests that being pregnant with a girl may affect how the mother’s body responds to illness.


A team of researchers from Ohio State University Wexner Medical Center set out to examine whether or not there is a connection between the sex of the baby and the mother’s immunity.


The team was led by Amanda Mitchell, a postdoctoral researcher in the Institute for Behavioral Medicine Research at Wexner.


The research was triggered by both anecdotal evidence and scientific studies (referenced by the authors) that suggest that the sex of the fetus influences several physiological responses in the mother. Glycemic control, blood pressure, and cortisol levels have all been shown to differ according to the sex of the fetus.


In the new study, Mitchell and team examined 80 women in the early, middle, and late stages of their pregnancies. Of these future mothers, 46 were pregnant with males and 34 with females. Researchers exposed their immune cells to bacteria to see whether they responded differently depending on the sex of the fetus.


The new findings were published in the journal Brain, Behavior, and Immunity.

Female fetus raises pro-inflammatory cytokine levels


More specifically, Mitchell and her colleagues examined the levels of cytokines in pregnant women. Cytokines are signaling molecules that regulate immunity and inflammation.


They are sometimes called emergency molecules because they are released by the body to fight off sickness, as they help cells to communicate with each other when there is inflammation in the body. Cytokines are part of the body’s natural immune response, but they can cause disease when released persistently. This is similar to how inflammation is a crucial component of the immune response, but too much of it can cause achiness and fatigue.


The study analyzed cytokine levels both in the blood and in the bacteria-exposed laboratory sample.


The findings suggest that women pregnant with girls may experience more severe symptoms of certain illnesses.


“While women did not exhibit differences in blood cytokine levels based on fetal sex, we did find that the immune cells of women carrying female fetuses produced more pro-inflammatory cytokines when exposed to bacteria. This means that women carrying female fetuses exhibited a heightened inflammatory response when their immune system was challenged, compared to women carrying male fetuses.”


The increased inflammation noticed in this study could explain why women pregnant with female fetuses tend to have more severe symptoms of pre-existing medical conditions. Examples given by the researchers include asthma and allergies, which are both conditions appearing to be exacerbated when carrying a female fetus compared with a male one.


The study’s lead investigator explains the significance of the findings:

“This research helps women and their obstetricians recognize that fetal sex is one factor that may impact how a woman’s body responds to everyday immune challenges and can lead to further research into how differences in immune function may affect how a woman responds to different viruses, infections, or chronic health conditions (such as asthma), including whether these responses affect the health of the fetus.”

Amanda Mitchell


More research is needed to understand exactly how pregnancy affects inflammation. Mitchell speculates that sex hormones, or other hormones found in the placenta, may affect inflammation levels.


“It is important to think about supporting healthy immune function, which does not necessarily mean boosting it – it is problematic to have too little or too great of an immune response,” Mitchell adds. “That being said, research has shown that exercise supports healthy immune functioning, as does eating some foods, like leafy greens, and relaxing with activities like meditation. Of course, it is always important to check with your healthcare provider before making any changes to your routine or diet,” she notes.


Furthermore, the authors point out that more information is required on the relation between fetal sex and other pre-existing medical conditions in the mother (such as preeclampsia), as well as negative pregnancy outcomes (such as preterm birth).

Learn about pre-pregnancy genetic testing, and what women and doctors should know.


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