A health advocacy group is angry MedSafe hasn't made concerns about allegedly dodgy pregnancy tests more widely known.
The Government-owned agency issued a warning on its website about EasyCheck, which has reportedly returned some false readings.
Auckland Women's Health Council coordinator Lynda Williams says the alert should have been better publicised.
"It's not good enough for MedSafe to rely on women knowing where to go looking for a warning that this particular pregnancy test kit is not very effective."
If women get tested and the result comes back negative, Ms Williams says they may go on to drink alcohol or take drugs and unwittingly harm their unborn baby.
"Also if this is an unwanted pregnancy, then it delays their decision-making around what to do about that, so this has got quite severe implications."
MedSafe says it is "continuing to monitor reports" relating to the Chinese-made EasyCheck test, which is supplied by Phoenix MedCare. It's funded by Pharmac, and used by doctors, midwives and other health workers. It's not available over-the-counter.
Phoenix says it has only heard of two cases of false negatives, both unconfirmed, out of 500,000 kits it has supplied since July last year. It has done tests of its own and found nothing wrong.
"Our conclusion is that any false negative result is likely due to incorrect procedural or storage techniques," says spokesperson Brad Rodger.
"We have only been able to replicate this issue by purposely follow an incorrect testing method such as shaking the product after the test has been taken."
MedSafe says it will monitor reports of the product until November, but Ms Williams doesn't think that's good enough.
"I'd like to see MedSafe go public about this and ask the company to withdraw their product."
For a pregnancy test with 99 percent accuracy, 5000 out of every 500,000 tests could potentially be wrong. But if a pregnant woman takes the test twice, there should only be a 0.01 percent chance of both tests show up negative.