Too much vitamin A can cause development defects in unborn babies but many women do not consider the vitamin's presence in most multivitamin supplements, says the charity BDF Newlife.
And the charity says it has anecdotal evidence from its helpline that many women planning a pregnancy take a general multivitamin supplement in the belief that they are doing the best thing for them and their baby.
However a recent survey by the Oxfordshire brand of the UK's Trading Standards has found a third of multivitamin products tested did not carry a warning for pregnant women about vitamin A.
Vitamin makers are not required to include a warning on their products but the Trading Standards official says that the fact that some manufacturers are doing so, suggests that an industry-wide standard could easily be introduced.
"Almost two thirds of the multi-vitamins we checked carried a warning for pregnant women, so it is hard to understand why the industry as a whole hasn't adopted a consistent approach," said Nigel Strick, head of Oxfordshire's Trading Standards, which carried out the survey.
David Adams, director of the UK's Health Food Manufacturer's Association (HFMA), says that the organisation's code of practice for all member companies supplying food supplements requires a warning to pregnant women on all supplements providing more than 800mcg of preformed vitamin A (as retinol) daily.
He added however that in meetings between industry organisations and the Food Standards Agency that culminated in last year's agreement to add advisory statements to labels of various food supplements, it was agreed to review vitamin A labelling when a pending safety study on the vitamin by the UK's scientific advisory committee on nutrition had been completed.
"The HFMA itself, in its submission to SACN, has suggested significant extension of the advice given on Vitamin A labels," said Adams.
The Trading Standards authority found that, between November last year and March this year, 20 out of 60 multivitamin products did not carry vitamin A warnings, including brands such as Sanatogen, Centrum and Quest.
Strick added that if manufacturers did not agree to label products, then moves would be made to introduce compulsory legislation.
"Someone needs to take this seriously very soon or else we will have to look at compulsory procedures," he told NutraIngredients.com