Genworth Mortgage Insurance Australia suffered a substantial fall in net profit in the March quarter after it suffered a big fall in gross written premium.Genworth reported net profit for the quarter of A$67.3 million - down 24.8 per cent on the previous corresponding period. After adjusting for investment returns, underlying net profit was down 11.5 per cent to $61.7 million.Gross written premium fell 33.4 per cent to $85 million.Genworth chief executive Georgette Nicholas said in a statement that the fall in gross written premium was a result of changes in the mortgage market, specifically the decline in the proportion of high loan-to-valuation ratio loans being written.The fall in premium also reflected the impact of Westpac's decision last year not to renew its contract with Genworth. Nicholas said the company underwriting performance was strong, with a loss ratio of 27 per cent, compared with 25.3 per cent in the previous corresponding period (the loss ratio measures net claims as a proportion of net earned premium)."Given current market condition, we remain focused on maintaining our risk management discipline," Nicholas said.Genworth paid 280 claims during the quarter - the same as in the previous corresponding period. The average claim was $65,800, compared with $62,500 in the March quarter last year.There were 2697 new delinquencies, compared with 2401 in the December quarter and 2679 in the March quarter last year.Total delinquencies were 5889 and the delinquency rate was 0.4 per cent, compared with a rate of 0.38 per cent in the December quarter and 0.36 per cent in the March quarter last year.