Australia's largest direct provider of lender's mortgage insurance, Genworth, has recorded a sharp turnaround in first quarter profit after crystalizing monster gains on its investment portfolio.Genworth boosted its March quarter profit by A$39 million to $47.8 million as growth in new insurance written also improved during the period.Disclosure of the profit bounce came as managing director Georgette Nicholas announced plans to leave the company later this year.Chairman Ian MacDonald said Nicholas had agreed to remain in the role until the board found a replacement."Georgette has played a significant role in leading Genworth's strategic program of work, particularly in redefining the company's core business model and in positioning Genworth as a leading provider of risk and capital management solutions to the Australian residential mortgage market," said MacDonald.New insurance written during the quarter climbed by more than $1 billion or 24 per cent to $5.4 billion.But the big driver of the bottom line was the big surge in investment income, including an unrealised gain of $25.5 million on the investment portfolio.Genworth reported an unrealised loss of $11.5 million on the portfolio in the 2018 March quarter.Delinquencies on the insurance book rose by $430 million or 7.6 per cent to $7.49 billion in the latest period.That equated to an eight basis point rise in the delinquency rate to 0.57 per cent."This was driven primarily by an increase in delinquency rates year-on-year across all states, particularly in Western Australia, New South Wales and Queensland," the company told the ASX in a filing.Genworth's ASX-listed scrip closed up 8 cents to $2.47.