(Sharecast News) - Shares in Bonmarche tumbled on Tuesday after the womenswear retailer warned of a worse-than-expected full-year loss - its third profit warning in six months - as trading since the beginning of March has been "significantly" weaker. The company said in an update that it now expects an underlying pre-tax loss of between £5m and £6m for the year to the end of March, compared to a previous forecast of £4m.The group, which discounted heavily in January and February to clear stock, said that while sales since Christmas had been slightly above the level required to meet the revised forecast range, trading since the start of the month has been significantly weaker, reversing sales gains made in the previous months."In light of this, we now believe there is a likelihood of sales levels for the remainder of the month continuing to follow this trend," it said, hence its expectations for a worse-than-expected full-year loss. The group pinned the recent downturn in trading on demand for transitional ranges, between winter and spring, having been satisfied during January and February."Although sales of spring season stock benefitted from the spell of warm weather in late February, this is not yet a large enough part of the sales mix to compensate for the lower demand for transitional stock," it said. "Nevertheless, on the basis of this positive early reaction to the spring product, our expectation for FY20 remains unchanged."At 0910 GMT, the shares were down 17% at 30.80p.