Just four doctors provide late-term abortions in the US. They are the subject of a new documentary that chronicles their work.
Only one movie at last week's Sundance Film Festival was so heavily guarded that the premiere required armed security and metal detectors.
But the stringent measures were not imposed to protect A-list celebrities, or the high-priced jewellery they sometimes wear to red-carpet events.
Instead, the ring of steel was there to ensure the safety of LeRoy Carhart, Warren Hern, Susan Robinson and Shelley Sella.
They are the four doctors who feature in After Tiller, the documentary by filmmakers Lana Wilson and Martha Shane.
George Tiller, one of the most prominent abortion doctors in the US, was assassinated in 2009 while worshipping at his local Kansas church with his family.
In the wake of Tiller's death, filmmaker Wilson found herself confounded by its irony - a man being killed in church by a religious zealot - and struck by the doctor's dedication.
"Why on earth would someone risk so much for so little reward?" she asked.
"I wondered who was left to carry out third-trimester abortions, his specialism, now he was gone."
Before his death, Tiller trained the four remaining doctors.
They are now scattered across the country - 71-year-old Carhart in Maryland, 74-year-old Hern in Colorado, and Robinson and Sella, both in their 60s, working out of the same clinic in Albuquerque, New Mexico.
While it took over a year to convince Sella and Robinson to participate, Carhart and Hern agreed quickly.
"I have always been of the opinion that it doesn't matter what people hear; if they want us dead, they'll kill us anyway," says LeRoy Carhart.
For Hern, the film provided a chance to educate the public about what he does - a mission he feels the pro-choice movement has failed to do.
"They see us as cartoon cut-outs, not patient-care providers."
The film comes on the 40th anniversary of Roe v Wade, the Supreme Court case that established abortion rights in the US.
And while a recent NBC/WSJ poll found that most Americans are in favour of some form of legalised abortion, late-term abortions, which account for 1% of all terminations, are still overwhelmingly unpopular.
A 2011 Gallup poll found that the vast majority of both pro-abortion and anti-abortion Americans thought these procedures should be illegal.
Though the abortion debate is one of the most polarising in the US, the film tried to present the doctors' work without the political context, shooting the film in a fly-on-the-wall style without comment.
"The abortion debate has become a shouting match for my generation," says co-director Shane.
"We would like to move the conversation to having a more honest discussion about what is a far more complex issue than either side of the argument are currently allowing it to be."
The film profiles several couples seeking an abortion due to foetal abnormality: their latest scans have shown that their child would not survive for long outside the womb, and, they are told, would be in great pain.
The doctors say most late-term abortions are carried out for this reason.
Other case studies in the film include a teenager who was raped and in denial of being pregnant; a woman who says she cannot feed another mouth in her household; and a 14-year-old-girl who is expecting for the second time and threatening to commit suicide.
"My respect for the doctors has increased tenfold, but that's not because of the fact they're risking their lives," says Shane.
"They're helping women with one of the most difficult things they'll ever go through.
"Women who wanted a baby and find they have severe anomalies, they help them grieve for their loss.
"Women who are there for other reasons, they're also there to make sure if this is the right decision for them.
"The work they are doing is so much more emotionally complex than anyone imagines."
Still, says Robinson, it is not a job without struggle.
"We have turned down a lot of women for abortions, and carried out a lot of procedures too, with a heavy heart," she says.
"But, generally speaking, if a woman has come, travelled for miles, and braved the protesters outside the door, then I know she is committed to her wishes."
Over the years, the documentary reveals, pro-life activists have targeted Carhart's stables, burning it and killing 21 horses; they've made hate phone calls to Hern's mother, who is in her 90s, and shot out the windows of his office. All four doctors have received death threats.
And every day, they face a barrage of protesters waiting for them at work. They remain undeterred.
"If not us, who will do it?" says Carhart. "I would do this all again, if I had my time over, despite what's happened to me.
"At the end of the day, it is about healthcare. We are providing a service to women."
Once these doctors are gone, it's unclear who will provide women this service and if it will still be accessible.
The Albuquerque clinic is training a new doctor, but eight states have amended their abortion law to prohibit the procedure after 20 weeks.
After Tiller received a standing ovation at its screening, but pro-life websites and blogs have condemned it for glorifying abortion and the doctors who perform the procedures.
The documentary is now being sold with a view to a cinema release.
In the meantime, the doctors are going back to work.