Pregnant Women May Experience Different Symptoms Depending on the Baby’s Sex

A team of researchers has found that pregnant women experience physiological changes depending on the sex of the baby they’re carrying. This can contribute to differences in the immune system’s inflammatory response. Pregnant women have often said they can “feel” a difference between fetuses of different sexes and now there is science to back this up. The details are in a paper that was just published in the journal Brain, Behavior, and Immunity.

Pregnant women have repeatedly claimed that they feel differences when carrying babies of specific sexes. These anecdotes have generally been ignored and there had been no studies on whether or not the fetal sex affected body chemistry. One possible explanation would be differences in cytokine levels, a huge group of proteins that are used in cell signaling. They are generally secreted by immune system cells and have effects on the surrounding cells. Cytokines can affect everything from the immune response to growth and hormone production. If the fetal sex affected cytokines, it could explain the differences in how a woman’s body reacts to the fetus.

Scientists from the Ohio State University Wexner Medical Center recruited 80 pregnant women and took blood samples throughout the pregnancies. The team recorded blood cytokine levels but also recorded the concentration of cytokines produced by immune cells. To measure those, the researchers exposed immune cell samples to bacteria and recorded the response.

The researchers found that while blood cytokine levels weren’t dependent on the sex of the fetus, there was a difference in immune response. Immune cell samples taken from women carrying female fetuses secreted more pro-inflammatory cytokines when the cells detected foreign bacteria. This resulted in a higher inflammatory response. While inflammation is a good sign that the immune system is functioning properly, too much inflammation can put stress on the woman’s body. This might explain why the women in the study who were carrying female fetuses were more likely to suffer from maternal asthma and other symptoms caused by excessive inflammation.

The team’s findings show that there are clear differences in immune system responses between fetal sexes. Female fetuses were associated with higher levels of cytokine production when immune cells were exposed to foreign bacteria. The team would need to conduct more research to find out why this occurs but one theory is that the differences in hormone production could affect the immune response.


Mitchell et al. Fetal sex is associated with maternal stimulated cytokine production, but not serum cytokine levels, in human pregnancy. Brain, Behavior, and Immunity (2017).

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