Re/insurer Arch Capital Group posted a first-quarter profit last night of $251 million. The company’s net income of $1.85 a share compares to $157.8 million, or $1.14 per share, for the 2012 first quarter.Gross premiums written by the insurance segment in the first quarter were flat from the 2012 first quarter, while net premiums written were 2.8 percent higher than in the 2012 first quarter. The company said the higher level of net premiums written primarily resulted from increases in programmes, national accounts, construction and accident and health lines.Arch said growth in casualty business primarily resulted from new accounts while the increase in other specialty primarily resulted from renewals of the credit and surety business acquired from Ariel Reinsurance in April 2012.Arch also reported after-tax operating income available to common shareholders of $158.7 million, or $1.17 per share, for the first quarter, compared to after-tax operating income available to common shareholders of $113.7 million, or $0.82, for the 2012 first quarter.The company said after-tax operating income or loss available to common shareholders represented an annualised return on average common equity of 12.9 percent for the 2013 first quarter, compared to 10.4 percent for the 2012 first quarter, while the company's net income available to common shareholders represented an annualised return on average common equity of 20.4 percent for the 2013 first quarter, compared to 14.4 percent for the 2012 first quarter.Arch said the combined ratio of insurance and reinsurance subsidiaries consisted of a loss ratio of 53.1 percent and an underwriting expense ratio of 31.5 percent, compared to a loss ratio of 58.1 percent and an underwriting expense ratio of 32 percent for the 2012 first quarter.Net investment income for the first quarter was $65.7 million, or $0.48 per share, compared to $73.8 million, or $0.53 per share, for the 2012 fourth quarter, and $74.3 million, or $0.54 per share, for the 2012 first quarter.