Only use pregnancy tests
Royal College of Obstetricians and Gynaecologists spokesman Mark Kilby said only pregnancy tests should be used.
The strange toothpaste method works by detecting the hormone human chorionic gonadatrophin (HCG), which is made by pregnant women.
Standard pregnancy tests, which can be bought at supermarkets and pharmacies, use the same technique - and are proven to be 99 per cent accurate.
"No evidence it works"
Kilby told MailOnline: "There is no evidence that toothpaste can detect HCG in a woman's urine.
"Women should not rely on DIY methods to confirm if they are pregnant or not. If a woman suspects that she may be pregnant, she should take a pregnancy test."
How did it come to light?
The bizarre toothpaste method came to light following a series of YouTube clips that demonstrate how to do the test.
Such footage, watched by millions, has been behind a spike of women checking out the trend on Google, figures suggest.
Advocates say the technique works better early in the morning when urine has the highest level of HCG.
Don't take it too seriously
Oxford Online Pharmacy chief pharmacist Stuart Gale told the Huffington Post that the test shouldn't be taken too seriously.
"The fizz in the toothpaste is caused by the acid in the urine reacting with the calcium carbonate in the toothpaste to give off carbon dioxide.
"The more acidic the urine is, the greater the fizz. Whether or not a person is or isn't pregnant wouldn't make any difference."
Toothpaste fuelling drug resistance?
Meanwhile, a common ingredient in toothpaste could be causing antibiotic resistance and fuelling the spread of superbugs, research this month hinted.
Scientists found triclosan, a chemical found in toothpaste, could be making bacteria more immune to antibiotics.
The study found bacteria exposed to triclosan could become more resistant to a group of antibiotics known as quinolones, commonly used to treat urinary tract infections, sinusitis, bronchitis and pneumonia.