If microbes like bacteria and fungi do end up colonizing an embryo (which is how humans develop a microbiome) then why can’t they infect/kill the embryo if it’s immune system hasn’t been properly developed yet. It’s also to my understanding that the mother’s immune system wants nothing to do with the embryo. What’s really happening here?
In: Biology
Inside the amniotic sac is sterile, and colonisation and the microbiome begin at birth. It is believed that is one reason why the vagina is so close to the anus, and why having a c section can mess up a baby’s microbiome.
Infections can occur in the amniotic sac (chorioamnionitis) and if the waters are broken, pathogens can travel up into the amniotic fluid and infect the fetus, but this is somewhat uncommon, can make a fetus very sick and is a common cause of preterm labour.
Antibodies from the mother do pass through to the fetus to some degree, giving the baby some protection (passive immunity)
the embryo developps inside an imperviuous bag (the amniotic cavity). it is filled with sterile liquid (amnotic fluid). It’s exchange with the ouside world come from the mother blood wich is supposed to be sterile also and that blood is filtered by the placenta to make it even more adapted to foetus needs.
the embryo can be infected in 2 situations:
1° Mums is infected and the microbial agent is able to get from her blood to foetus blood ( when he as the ability to cross the placenta barrier). That one of the way babies can be born with HIV for example.
2° Amniotic sac breaks and outside “dirt” can enter de amniotic fluid. It is not current and it happens with specific conditions ( vanilla sexual intercourse does not break the sac).
Certain things can pass from mother to fetus, but there is no direct blood-blood connection between the two. The mother’s bloodstream exchanges nutrients and waste products with the fetus’s bloodstream on pretty much a molecular level through capillaries in the uterine wall and the placenta. These molecules diffuse through the capillary walls, but larger things (bacterium and the mother’s macrophages, for example) are simply too large to pass between the two by capillary diffusion.
So the fetus is not (generally) exposed to pathogens in the womb. The birthing process begins the bacterial colonization of the baby, which continues rapidly through skin to skin contact with the mother (and others).
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