When Clementine Bastos was trying for a baby, her GP recommended the AMH test, also known as the "egg-timer test".
It measures the level of anti-Müllerian hormone (AMH) in a woman's blood to estimate her ovarian reserve.
"It came back low. That stressed me out," the 42-year-old from Sydney/Gadigal Country says.
Clementine's GP recommended she and her husband see a fertility specialist. While starting investigations with that clinic, the then 35-year-old got a surprise.
"I got sent off to do my bloods and turns out I was pregnant, three weeks."
New research led by Flinders University has found nearly one in five women who took the AMH test received a result classified as low.
However, among those who repeated the test after a low result, about one-third later received a result in the normal range.
Despite the test's unreliability, co-author of this new study, Tessa Copp, a senior research fellow in the school of public health at the University of Sydney, says there has been "massive growth" in testing.
"Which is particularly concerning given the number of women receiving a low result and potentially altering their family planning on the basis of that result," Dr Copp says.
Growing evidence AMH test can't predict ability to get pregnant
Analysing health records from almost 1.4 million Australian women, the researchers found AMH testing increased more than 13-fold between 2011 and 2021.
Women aged 30 to 34 experienced the sharpest rise, with test rates increasing almost 20-fold.
AMH testing is not covered by Medicare and can cost more than $100.
"The AMH test is useful for when undergoing IVF, because it can give an indication of how many eggs might be retrieved from a cycle," explains Dr Copp.
"[In that context] it's useful for expectation, and also if a woman has high AMH she might be at risk of hyper-stimulation.
"That's where the benefit stops."
She says despite "evidence consistently showing" AMH level is not associated with the chance of conceiving, or how long it will take to get pregnant, the rise in testing is likely linked to women delaying having their first child and a growing awareness of fertility issues.
Dr Copp says "false and misleading information" via social media and commercial promotion is also to blame.
Test causing panic and anxiety
Clementine says she feels the AMH test and discussions she had with a fertility clinic were "fearmongering".
"I was crying at home that we're never going to get a kid. The whole thing was a f***ing nightmare.
"The test [supposedly] tells you something is wrong, you get sent to a clinic … while [I was] sitting there already pregnant."
Dr Copp says it might be "hard for people to see how the AMH test can be harmful", but for some women it has the potential to cause "anxiety and distress" that they may be running out of time to have a baby. Or a "high result" might provide false reassurance they can delay pregnancy.
Karin Hammarberg is an adjunct senior research fellow at Monash University with 20 years' experience as a clinical coordinator of IVF programs.
She says the AMH test can have a "snowball effect", triggering women to have costly treatments such as egg freezing or IVF when they don't need medical intervention.
"It's a cascade of events we really need to make women more aware of.
"This test makes you more confused than insightful and has real-life consequences."
Trying for a baby, age only reliable way to gauge fertility
Luke Grzeskowiak, a pharmacist and researcher at the Flinders Health and Medical Research Institute, led the recent study of AMH testing and says the findings highlight the need for better education of both clinicians and the public.
"AMH testing can be useful in some specialist fertility settings, but it should not be mistaken for a test that predicts whether a woman will be able to have a baby," Dr Grzeskowiak says.
"The best way to support women is with accurate, evidence-based information, so they can make informed decisions about their reproductive health and future family plans."
Dr Copp says the only real test of fertility is "trying to get pregnant when you're ready".
"It's a really frustrating answer that you're not going to know until you try."
Dr Hammarberg says age is the most important factor when understanding fertility.
She says if you want children, it's important to understand the biology of reproduction. Fertility declines with age, but doesn't "fall off a cliff" at 35, she says.
"You only need one egg for conception.
"Trying now is the only way to know if you are fertile [but] people don't always have a choice … You might not have a partner or the financial resources.
"But if you want to leave [having a baby] until later, but have a plan, just get yourself as well informed as possible and make the best decision you can."
Where to get evidence-based information
Dr Copp recommends women curious about their fertility chat to their GP.
She says there is also a lot of evidence-based information that women can access for free and recommends the government website Your Fertility as a starting point.
For those trying to boost their fertility, she says "all the boring stuff" such as having good knowledge of your menstrual cycle, eating well, exercising, not smoking and avoiding too much alcohol may help.
Before undertaking any test or treatment, Dr Hammarberg suggests looking at these "5 questions to ask your doctor or other healthcare provider".
She says while we should expect our questions to be answered honestly, women need to be "self-aware and more demanding of the information".
"Women are capable of making good decisions, but they need the correct information."