Insurer AIG exceeds profit estimates on strong underwriting gains

May 4 (Reuters) - American International Group Inc beat market estimates for first-quarter profit on Thursday, as record underwriting gains cushioned the blow from lower alternative investment returns.

AIG, one of the world's biggest commercial insurers, said net premiums written in its general insurance for the quarter ended March grew 5% to $6.97 billion.

Adjusted after-tax income attributable to the company's common shareholders climbed to $1.63 per share, from $1.49 per share a year ago. Analysts on average had expected $1.42 per share, according the Refinitiv IBES data.

Total consolidated net investment income rose 9% to $3.5 billion, partially offset by lower alternative investment income, AIG said.

Rising interest rates and a banking crisis that led to the fall of three U.S. lenders roiled markets and pose a risk to parts of insurers' investment portfolio.

"The environment we operate in is continually shifting and remains volatile and unpredictable...," said Chief Executive Officer Peter Zaffino.

The New York-based company's general insurance underwriting income rose 13% to $502 million, its strongest first-quarter underwriting results, the insurer said.

The general insurance accident year combined ratio was 88.7%, compared with 89.5%, a year earlier. The metric excludes catastrophe losses and a ratio below 100 signifies that the insurer earns more from premiums than it pays out in claims.

Last month, peer insurer Travelers Companies Inc reported a fall in profit as catastrophe losses soared due to storms in the United States in March.

Corebridge Financial, whose largest shareholder is AIG, is set to report quarterly results next week. (Reporting by Siddarth S and Noor Zainab Hussain in Bengaluru; Editing by Shailesh Kuber)