Why an amniotic fluid embolism occurs isn't well understood.
An amniotic fluid embolism occurs when amniotic fluid or fetal material enters the maternal bloodstream, possibly by passing through tears in the fetal membranes. It's likely that amniotic fluid contains components that cause an inflammatory reaction and activate clotting in the mother's lungs and blood vessels.
However, amniotic fluid embolisms are rare — and it's likely that some amniotic fluid commonly enters the maternal bloodstream during delivery without causing problems. It's not clear why in some cases this leads to an amniotic fluid embolism.
Further research on what causes amniotic fluid embolisms is needed.