(NEW YORK) -- 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 ABC News.
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."
Copyright 2013 ABC News Radio