Fitch Ratings yesterday provided a preview, in a media release, of a more detailed report on the incidence of mortgages stress the firm will publish today. The firm publishes the most detailed local data on mortgage stress, based on its database of securitised mortgage pools. With $160 billion of mortgage pools monitored by Fitch, the firm's data covers about 18 per cent of the mortgage market.Of the ten worst performing regions, eight are in western or south-western Sydney or within the city's commuter belt. However, growth corridor suburbs of Sydney do not, on the whole, feature in the Fitch list with the stress instead concentrated in older suburban areas with few new housing developments and an older housing stock.The other two are in growth corridors of Melbourne. On a single postcode basis, several suburbs in south-west Sydney continue to dominate the top 10. Fitch said the worst performing postcode was Wetherill Park in Sydney, where 6.7 per cent of mortgages in the agency's sample were in arrears by one or more mortgage payments at the end of March 2008. Other postcodes in the top 10 were Helensvale on the Golad Coast; St Mary's, Sydney; Kurrajong, in the Blue Mountains; Guildford, Sydney; Punchbowl, Sydney; Lake Illawarra, Woolongong; Greenacre, Sydney; Rooty Hill, Sydney; and Fairfield in Sydney, with arrears of 5.0 per cent. Most of the problem locations in Sydney are not in classic outer suburban growth areas but rather in areas where the property price bubble of 2002, itself a feature of the lending bubble (and predatory lending practices) of the time reached their zenith.  Nationwide, the level of mortgage arrears remains largely benign.Fitch wrote in its media release that on a national basis, 1.88 per cent of mortgages nationwide were more than one month past due, while 0.73 per cent of mortgages were more than three months past due. While regional patterns vary, and delinquencies are lowest in Western Australia, Fitch noted that mortgage performance in WA is deteriorating at the fastest rate of all the states.