Endometriosis affects at least one in every 10 New Zealand women. Its symptoms include severe pain, it can cause fertility problems, and it costs the public health system an estimated $1 billion a year.

But surprisingly little is known about the underlying causes of this chronic disease, in which pieces of endometrium, the innermost lining of the uterus, lodge and grow outside the uterus.

Internationally, the average delay before diagnosis is between 8-11 years, and experts believe the actual incidence of the disease is far higher than the numbers diagnosed - around 120,000 women in New Zealand and 176 million worldwide.

JASON DORDAY/Stuff.co.nz Myken Stewart of NZ Fashion Week talks about women with endometriosis.

A particularly frustrating element for those who suffer it - as well as frequent misdiagnosis and a lack of awareness of the disease - is that the treatments currently in use are not effective for all women.

READ MORE:

* Young women with endometriosis becoming opioid addicts

* Endometriosis: the silent crisis affecting relationships

* Lena Dunham describes long relationship with endometriosis

Your endo experience Share your stories, photos and videos. Contribute

Steroids such as oral contraceptives are the main treatment, but are only successful for half of women who receive them - and those women generally develop resistance to their specific treatment.

Some undergo laparoscopies (keyhole surgery) to remove the rogue endometrium and scar tissue, and others undergo entire removal of the uterus or ovaries, but even surgical treatments don't always prevent the tissue growing back elsewhere.

However New Zealand research into the cause of endometriosis is offering fresh hope for future treatments that target the disease at its roots.

123rf "It feels like someone stabbing you with a butcher's knife, over and over and over again."

Dr Anna Ponnampalam, a reproductive biologist at the Liggins Institute and the University of Auckland Department of Obstetrics and Gynaecology, suspects the cause partially lies in chemical changes to DNA that may lead the uterus lining to respond abnormally to the hormone progesterone.

"If we can figure out the exact molecular pathway behind endometriosis, and what triggers it, we will have a good chance of developing effective treatments," says Ponnampalam.

Researchers hope to have early results next summer.

JASON DORDAY/FAIRFAX NZ Myken Stewart found out about her endo at 17.

Ponnampalam also plans to do a separate study to develop a new way of diagnosing endometriosis, which can currently be diagnosed only by laparoscopy.

"Because this is invasive, it puts some girls and women off," she says.

In the meantime, Kiwi women across the country battle to manage their conditions, determined not to let endometriosis stop them from living their lives.

Myken Stewart is one of those who won't be turning to laparoscopy as a solution.

"It's a horrible, invasive operation, and I don't believe it's the right thing for everyone with endo because it creates more scarring," says Stewart, 46, who first discovered endometriosis ran in the family when she was living in Brazil at the age of 17, and had two laparoscopies in her early 20s.

"While I was away my mum nearly died, she had a grapefruit-sized endo growth inside her. She was one of the first people to be treated with drugs for shrinkage, and then eventually with an operation to get it out.

"I don't ever want to have that operation again, it's hideous. They go in, they see if there's something there, they take it out, and it's more scarring, a $5000 operation and you feel terrible for ten days afterwards. For me, it's not the right way."

Instead, she tries to manage the disease through diet, yoga and ayurvedic medicine, and recently began a trial of progesterone-only contraception at the recommendation of her gynecologist​ Mike East, who says it "may slow the progression of endometriosis as it tends to reduce the growth of healthy endometrium and endometriosis alike."

Stewart, who until recently owned and ran New Zealand Fashion Week with her mother Pieter - both are still involved but have taken a step back - says the pain "feels like someone stabbing you with a butcher's knife, over and over and over again".

"For 10 years I've been walking around at Fashion Week with a mini hot water bottle down my pants.

"There's been times when I've felt like I was going to faint, and I've had to take myself out for 15 or 20 minutes and wait for the heat to get into the pain.

"It's just this silent thing, the pain, it takes me into another headspace."

Courtney Meredith, 30, a renowned writer and musician, describes her endometriosis as feeling "like your ovaries are on fire, like you're being stabbed from behind, and like someone has filled your entire body with cement".

She remembers the first time she was doubled over with pain, walking across the school yard with a friend, at just ten years old.

"That really was the beginning of the pain for me. So my experience of becoming a woman, my experience of my body, has always been that I'm in pain a lot of the time.

"I wasn't properly diagnosed until after my first surgery, when I was 23, so before then it was just trial and error, lots of different meds..."

Meredith says for her, "the really tough part is just that constant emotional negotiation."

"Your body's producing so much estrogen, you're out of balance, you're in all this pain but you're also trying to keep perspective, to be quite careful with yourself when you're in situations that are a bit trying, when people are asking something of you - which for any other person would be fine but because you're in that state they're actually asking a lot."

Like Stewart, she's turned to managing the disease through diet and lifestyle - no coffee, no sugar and few carbs, practising mindfulness, gentle exercise ("I'm at the gym but I can't really do the circuit training I want to do because it takes my body one or two weeks to recover from it") and visits to both ayurvedic specialists and counsellors where required.

"I'm really open with people that going to see a therapist or a counsellor to get through, there's no shame in that. I've got someone I go to see to get my perspective back or to plot my next move.

"You have to plan ahead. Anywhere I go. I've got trips coming up later this year and I plan those trips with my GP."

She also had a Mirena (a hormone-inducing IUD) put in, which she describes as a blessing, now, though "it was actually initially excruciating".

"After I had that put in I had three weeks of contractions. It was really debilitating and I couldn't leave my house but I was still working, I was writing Tail of the Taniwha actually, and my deadline was two weeks out and I just had to push through.That was a really tough time."

Endometriosis runs in Meredith's family too, which is in itself a form of support, and draws the women together.

"All my aunties, grandmother, my cousins, it's something we all experience as women in this family, so there's people I can always talk to when I'm having a tough time.

"It's not all like, just breathe through it, there are moments when it just feels deeply unfair."