Many unsuspecting patients spend thousands of pounds on optional extras which are offered with a promise to improve their chances of having a baby.

But some clinics may be "unnecessarily offering unproven treatments to patients", the fertility regulator has warned.

Now those supplementary treatments, which can include genetic tests, drugs, surgery and equipment, are to be colour-coded by the Human Fertility and Embryology Authority (HFEA) to highlight any that are unproven or unsafe.

Under the new system of five colours and symbols, any that are green with a plus sign, have been classed as effective.

But if the add-on is coloured yellow with a plus-minus symbol, it isn't clear whether it works because the evidence is conflicting.

Embryo glue (also known as hyaluronate enriched pre-transfer culture medium), has been coded yellow.

It claims to help the embryo implant in the womb, but the HFEA has decided it isn't sure it improves the chances of pregnancy.

The regulator said it cannot rate the effectiveness of embryo "hatching" treatments or intrauterine cultures due to insufficient evidence, and both have therefore been rated grey with a question mark.

If the supplementary treatment is black with a zero in the middle, it has no effect on fertility treatments.

Endometrial receptivity testing, which purports to find the optimal time for an embryo to be transferred into a woman's womb, has been coded red, with an exclamation mark, meaning there are potential safety concerns.

Any add-ons coloured red may even hamper a couple's chances of getting pregnant.

The HFEA said that add-ons without strong evidence of their safety and/or effectiveness should only be offered in a research setting and patients shouldn't have to pay for them.

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HFEA chief executive Peter Thompson said: "People going through treatment are often spending a lot of money and want to have a baby as soon as possible and do everything they can to improve the chances of success.

"But when some add-ons cost hundreds or even thousands of pounds each, we want to make sure patients have the best available information."

"Clinics," he said, "must give patients a clear idea of what any treatment add-on will involve, how likely it is to increase their chance of a successful pregnancy and how much it will cost".

HFEA Scientific and Clinical Advances Advisory Committee chairman Professor Tim Child, said: "For the vast majority of patients, more rounds of proven treatment could be more effective."