The researchers measured the levels of antibodies in the expectant mother’s blood, and the fetuses’ antibody levels using placenta tissue and blood samples from the umbilical cords.
The results showed that the women pregnant with baby boys had fewer antibodies than those carrying girls. Additionally, pregnant women seemed to pass along fewer coronavirus antibodies to male fetuses than to females.
“There’s some crosstalk that’s happening between the fetus and mother’s immune system”, said Andrea Edlow, a maternal-fetal medicine specialist at Massachusetts General Hospital who co-led the study.
The findings may hint at broader differences in how men and women respond to COVID-19. Male fetuses seemed to develop an inflammatory response to the virus that wasn’t detected among female fetuses.
This inflammation may be interfering with a mother’s ability to pass coronavirus antibodies to her unborn baby boy.
Even in the placentas of women carrying male babies, there was a presence of genes, which promote inflammation but those same genes were under-expressed in the placentas of women with female fetuses.
Though these facts cannot explain the sex bias in COVID-19, it does give us some hints into male immunity in general that starts in utero.