In addition to hampering breathing, an amniotic embolism triggers an allergic reaction.
"Whether these two things happen simultaneously or one happens before the other is unclear," said Druzin.
Cottam went into the hospital suffering from pre-eclampsia, a potentially dangerous condition that causes high blood pressure. That, and the fact she was carrying twins, may have been risk factors, according to Druzin, who did not treat Cottam.
"We see it when the amniotic fluid is under pressure in very active labor where there are lots of contractions," he said. "Often the membranes are ruptured spontaneously or by the doctor and there is some entry into the circulation."
In most cases, according to Druzin, "the hole is never found."
As her pre-eclampsia got worse, Cottam's labor was induced. But all seemed to be going normally as she was readied for an epidural. Soon, the midwife noticed Cottam was coughing and struggling to breathe and doctors called for a C-section.
"When I was wheeled into the theater for my emergency cesarean section, I witnessed the medics running down the corridor and knew something was wrong," Cottam said.
She was taken to intensive care and placed on a life-support machine. It took three hours to stabilize Cottam because her blood wouldn't clot.
When Cottam finally came out of her coma 12 hours later, she had no idea her twins had been born.
"I felt very swollen, as if they were still inside me," she said. "It wasn't until a medic informed me that I was OK and that the twins were in neonatal but doing well, that I was realized that the outcome was good."
Dr. Leo Brancazio, associate professor of obstetrics and gynecology and head of maternal/fetal medicine at Duke University Medical Center, said amniotic fluid embolisms are "poorly understood."
"When it does occur, patients deteriorate quite quickly, so formal studies are very had to do," he said. "For some reason, there is an influx of amniotic fluid from the pregnancy into the mother's circulation. It happens more than we think, but it is of no consequence."
In pregnancy, large blood vessels from the mother feed into the placenta and some of them are veins.
"If there is a tear in the amniotic sac around or through the placenta, the amniotic fluid enters the mother's blood stream," Brancazio said.
The embolism sets off an anaphylactic reaction, constricting the bronchial tubes and shutting down the mother's airways. At the same time, a phenomenon known as disseminated intravascular coagulation or DIC occurs: The blood loses its ability to form a stable clot and the mother experiences a "profound" drop in blood pressure.
"The lining of the patient's blood vessels become temporarily injured and bleed, and you can't stop the bleeding," he said. There can also be brain damage because of lack of oxygen.
Historically, the condition was always fatal, but today with heightened awareness and better team approaches to obstetrics and anesthesia, more women like Cottam can be saved. Supportive care -- a respirator for breathing, medications to increase blood pressure; and fluids and blood products to start coagulation -- can restore the mother's cardiovascular system.
Such was the case with Cottam, who spent a week in the hospital, then was able to return home. The twins stayed two weeks in intensive care.
Since then, she has been in counseling for trauma, which Cottam said, "has helped me a great deal."
But she said her perspective on life has changed, and she is more relaxed as a mother to her 4-year-old daughter Olivia and the now the twins.
"The hospital after-care was amazing," Cottam wrote to ABCNews.com. "My girls are doing fine and developing well. I am physically very well and back to normal. I think about my experience every night before I go to sleep and shed a tear every now and then but hey, I'm here and that's all that matters."