The Adelaide mother gave birth to Indianna four weeks ago. Her daughter Zahra was born two years earlier, both after IVF.

Fertility treatment for the two girls cost a combined $32,000, including five failed attempts at IVF and a shopping list of add-on procedures.

There was the embryo glue, human growth hormone and a steroid called prednisolone she was offered by her fertility clinic after a scan detected a high number of NK cells.

The prednisolone only cost about $37 but the human growth hormone costs $1000 for two injections.

"Human growth hormone was very expensive, I thought," Ms Miller said.

"They say to you, 'It's your choice,' but then if you're facing a situation of having a baby or not having a baby and you've already paid thousands of dollars, it's not really a choice. You think, if this is the deciding factor, if it's going to make a difference."

Desperate couples are being sold unproven and expensive treatments by fertility clinics as the number of women seeking IVF treatment continues to rise.

About one in six couples in Australia are infertile, and the increasing age at which women are attempting to conceive, along with rising rates of obesity, have fuelled a booming fertility industry with two publicly listed companies and strong annual growth.

But some fertility specialists are concerned that add-on treatments and tests such as preimplantation genetic screening, NK cell testing and human growth hormone are ramping up the already steep out-of-pocket costs despite little proof of benefit and some evidence of risk.

None of the medical experts interviewed in this article were involved in Ms Miller's treatment.

A steroid treatment that suppresses the immune system in women with repeated IVF failure and is widely used in Australia and overseas has now been found to be based on the flawed premise that high levels of "natural killer cells" (NK cells) in the uterus jeopardise pregnancy.

The cells actually played an important role in establishing pregnancy and women who took drugs to wipe them out had higher rates of preterm birth, while their babies had higher rates of congenital abnormalities, according to the study published in Human Reproduction.

Lead author Sarah Robertson said women who were tested for NK cells often recorded high readings because the results varied widely between individuals, but there was no proof that these cells were problematic and the drug prescribed to reduce them – prednisolone – carried risks.

"For women with a rare autoimmune disease this is a good drug to take because it helps with their condition and also helps them achieve pregnancy, but what has happened in the fertility industry is that there's been an extrapolation that therefore this drug will help all women," said Professor Robertson, a reproductive immunology researcher at the University of Adelaide.

"The cost may not come until later in the pregnancy. You may get an increased implantation rate but what you really want is a healthy baby."

Studies showed the drugs doubled the chances of preterm birth and tripled the risk of cleft palate in their babies, with an anomaly rate of 4.6 per cent.

The $536 million fertility industry has been growing by 4.9 per cent annually since 2011, but the growth of bulk-billing providers since 2014 has threatened the market share of the three dominant players, Virtus, IVF Australia and Genea.

With rising out-of-pocket costs at the commercial clinics, the competition posed by bulk-billing operators such as Primary IVF has put pressure on the established players to maintain revenue growth, and prompted claims of over-servicing.

Couples generally pay $4000 to $4400 for an IVF cycle at the commercial clinics, while Medicare subsidises around $5300 per cycle, but procedures such as embryo freezing and storing cost extra.

Virtus chief executive Sue Channon reassured investors in August that the premium clinics trading under IVF Australia were continuing to perform well, partly because the average age of patients at 37 was driving the take-up of more complicated interventions.

These include services such as preimplantation genetic screening, which costs $700 per embryo and grew by 19 per cent in Australia between 2013 and 2014, but is believed by some specialists to be overprescribed.

Other controversial interventions include human growth hormone ($500 per vial), which a large trial concluded had little benefit, intracytoplasmic sperm injection ($4000), which has been described as "unnecessary, ineffective, costly care" and embryoscopes ($475), where embryos are monitored by a camera 24 hours a day but have little evidence behind them.

Among 37,281 women who had fertility treatment in 2014, more than a quarter were over the age of 40, by which age the chances of delivering a live baby are less than 10 per cent.

Monash IVF medical director Luk Rombauts said add-on procedures did not make any money for IVF companies because there was little mark up.

"Often when patients have had many treatments they become more desperate and doctors don't always have the answers," Professor Rombauts said.

"I can see why doctors put their thinking hats on and try something that's a bit more experimental, but that should be clearly explained to patients."

Treatments such as prednisolone for NK cells were cheap, but he did not prescribe it.

"It's almost like using a nuclear bomb to flatten a city if you see some terrorists hiding there.

"Yes, it will take them out, but there's an enormous amount of collateral damage."

But IVF Australia specialist Gavin Sacks, who pioneered the NK cell test and the prednisolone therapy that he dubbed "the Bondi Protocol" said while he agreed some patients were being unnecessarily prescribed, the treatment was valuable for many women based on his 20 years of experience and the risks were very low.

"It's been difficult to do randomised trials but I would see about 15 per cent of women who have repeated failures have very high level natural killer cells and these people do seem to do better when they have immune therapy," Dr Sachs said.

"What do you do with really problematic people? I really believe our duty is to the patient. Our job is to help them and to use whatever we can in science and technology to do that and we have to push boundaries and learn more."