Amniotic fluid embolism was first identified in 1926, but it still isn't fully understood today.
AFE is rare, unpredictable and unpreventable, accounting for between 5 and 10 percent of maternal mortality in the United States, and is likely triggered when amniotic fluid enters the bloodstream. However, by no means every woman who gets amniotic fluid in her bloodstream suffers an AFE.
Some estimates have AFE occurring anywhere from 1 birth in 8,000 to 1 in 30,000, with mortality running as high as 80 percent. Many women who survive AFE suffer life-altering brain damage.
A study published in the American Journal of Obstetrics & Gynecology in 2008 found AFE occuring in about 7.7 of every 100,000 births -- that's about 1 in 13,000 births, which makes it a rare event -- and still killing more than one in five mothers it strikes.
The authors of the AJOG article found associations between AFE and mothers older than 35, Caesarean births and "placental pathologies" like placenta previa, in which the placenta attaches low in the uterus, where it can cause hemorrhaging and other complications during a pregnancy.
However, the study did not find an association with artificial induction -- the use of drugs like Pitocin to start or hurry up labor.
AFE displays a cascade of symptoms that can include cardiac arrest and disseminated intravascular coagulation, or DIC for short. During a DIC, a person's clotting factor is deployed all at once, after which hemorrhage can ensue. A mother can die from these events and so can a baby who is still in the womb -- the saddest birth story of all.