Angela Cottam was in the middle of heavy labor with a set of twins when she suddenly began choking and turned blue.
"I felt like I had a tickly cough," said the 32-year-old elementary school teacher from Flintshire in Wales.
She didn't know it at the time, but the amniotic fluid surrounding the babies in her womb had leaked into her blood system and was quickly killing her. Cottam's lungs collapsed and she nearly bled to death.
Cottam and her twin girls survived, although she spent 22 hours in a coma at Countess of Chester Hospital in Britain. She had a tube inserted into her throat so she could breathe, lost seven pints of blood and needed 22 transfusions.
Her family was told she might not live.
"As I lay in ICU, Peter, my husband, went to hell and back with thoughts about life alone with twins and our 4-year-old daughter to bring up," she wrote in an email to ABCNews.com.
Cottam suffered a rare, but extremely dangerous event in childbirth -- an amniotic fluid embolism, which occurs only in about 1 in 10,000 pregnancies.
The fluid, filled with foreign cells from the unborn babies, traveled to her lung, setting off a quick chain reaction of events that could have led to cardiovascular collapse.
"It's a bad disease," said Dr. Maurice Druzin, chief of obstetrics at Lucille Packard Children's Hospital at Stanford University. "The bottom line is it's a sudden catastrophic event that causes mortality at a very high rate -- over 80 percent. But it's not very common.
"Essentially, a large amount of amniotic fluid from the sac around the baby entered the maternal circulation. It's actually quite complicated and the total reason for what happens is not 100 percent clear," he said. "It usually kills you pretty quickly."
Cottam and her now 8-month-old baby girls -- Amelie and Ava -- are healthy. But it was a frightening and grueling experience. Ava went three minutes without oxygen and had to be resuscitated.
"My husband and parents feared the worst, but during the ordeal I was calm, as I knew I was in the best possible place," she wrote. "The staff at the hospital were so calm and attentive and extremely quick to respond."
Cottam was told the amniotic fluid contained cells such as sloughed off skin, fingernail or hair from one of the twins.
"The consultant couldn't say what it was exactly, but said it was possibly one of those things," she wrote. "The emphasis was that it was so rare."
The British newspapers exclaimed in their news coverage: "Mum almost killed by unborn baby's fingernail," a headline Druzin called, "ridiculous."
"Amniotic fluid contains fetal cells and hair and maybe a fingernail, but it's a stretch to say it caused the embolism," Druzin said. "A relatively large amount of amniotic fluid is not supposed to be in the maternal circulation and it acts like a pulmonary embolism -- if it goes to the lungs it can cause an immediate reaction from a mechanical obstruction perspective."
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."