UnitedHealth Group Inc posted a higher-than-expected fourth-quarter profit on Thursday, helped by increased membership across its array of health plans.

The largest U.S. health insurer by market value also backed its 2012 earnings forecast, which many analysts have seen as conservative.

UnitedHealth's quarterly net income rose to $1.26 billion, or $1.17 per share, compared with $1.04 billion, or 94 cents per share, a year earlier.

Analysts on average were expecting $1.04 per share, according to Thomson Reuters I/B/E/S.

Revenue rose 8 percent to $25.92 billion, about $230 million ahead of estimates.

Membership increased to about 34.6 million, up 5 percent. The company reported gains in its Medicare plans for the elderly and Medicaid plans for low-income Americans, as well as in its commercial plans serving employers.

UnitedHealth backed its 2012 profit forecast, given in November, of $4.55 to $4.75 per share on revenue of $107 billion to $108 billion. Analysts are looking for 2012 earnings of $4.77 per share.

The company in November also forecast an increase in membership in 2012, to well above 35 million, as gains in its Medicare and Medicaid plans more than offset declines in some plans serving employers and individuals.

(Reporting By Lewis Krauskopf in New York; Editing by Lisa Von Ahn)