Dr. Lisa Moore, fellow of the maternal fetal medicine department of Obstetrics and Gynecology at the University of Mississippi, says that amniotic fluid embolism (AFE) is a rare obstetric emergency in which amniotic fluid, fetal cells, hair or other debris enters the mother's blood stream via the placenta and trigger an allergic reaction. This allergic reaction results in cardiorespiratory (heart and lung) collapse. According to Dr. Moore, statistics show that 50 percent of patients with AFE die within the first hour of the onset of symptoms and a high percentage of women who do survive have permanent neurological impairment.
Because most doctors never experience a patient with AFE, the exact process is poorly understood; however, it is believed that once the fluid and fetal cells enter the maternal pulmonary circulation a two-phase process occurs. Dr. Moore outlines the process:
In the first phase, the patient experiences acute shortness of breath and hypertension (extremely high blood pressure). This rapidly progresses to cardiopulmonary arrest as the chambers of the heart fail to dilate and there is a reduction of oxygen to the heart and lungs. Not long after this stage the patient will lapse into a coma.
Although many women with AFE do not survive beyond the first stage, about 40 percent of the initial survivors will pass onto the second phase. This is known as the hemorrhagic phase and may be accompanied by severe shivering, coughing, vomiting and the sensation of a bad taste in the mouth. This is also accompanied by excessive bleeding as the blood loses its ability to clot. As hypoxia (the reduction of the oxygen supply) progresses, the fetal heart rate may drop to less than 110 beats per minute, putting the fetus in distress.
Dr. Peter McLaren, member of the Fellowship of Australian and New Zealand College of Anesthetists (FANZCA), says that it is mostly agreed among medical professionals that this condition results from amniotic fluid entering the uterine veins, and that for this to occur there are three prerequisites:
- ruptured membranes (a term used to define the rupture of the amniotic sac)
- ruptured uterine or cervical veins
- a pressure gradient from uterus to vein
Although exposure to fetal tissue is common and thus finding fetal tissue within the maternal circulation is not significant, in a small percentage of women this exposure leads to a complex chain of events resulting in collapse and death.
Dr. Moore goes on to say that AFE affects all races and ethnic groups, and although it was previously thought to affect those of advanced age it has since been disproved, as has the original thought that AFE only occurred after a long, hard labor. AFE can occur before, during or after delivery and has also been known to occur during abortion, abdominal trauma and amnioinfusion (an infusion of fluid into the amniotic cavity when there is a lack of amniotic fluid).
Statistically, AFE occurs in an estimated 1 in 8,000 to 1 in 80,000 pregnancies. Ina May Gaskins, a certified professional midwife and President of the Midwives Alliance of North America says that incidence of AFE in the United States seems to be rising and is now one of the leading causes of maternal death in the United States.
Characteristic signs of AFE include larger than average babies being carried past their due dates, very hard labor before going into shock, high levels of anxiety, complaints of chills, shortness of breath and vomiting. Shockingly, maternal mortality is high with figures of around 80 percent, although the neo-natal survival rate is much better at 70 percent.
There is, however, no evidence to indicate that survivors of AFE are at risk for amniotic fluid embolism in future pregnancies, although the condition is considered to be unpredictable and unpreventable.
In the United States there is already a National U.S. Registry that was established in 1998 by Dr. Steven L. Clark, AFCOG, who is at the Department of Obstetrics and Gynecology, University of Utah School of Medicine. There are also plans for a confidential register of all cases of AFE to be established for the United Kingdom with the aim of identifying differences or common factors between survivors and fatalities with the hope that it may help to reduce the number of maternal deaths from this condition.