Cigna's fourth-quarter earnings dropped 37 percent compared to the same period last year, when the managed care provider recorded a $101 million gain related to the completion of an IRS audit. Results fell well short of Wall Street expectations, and Cigna shares tumbled in Thursday premarket trading. The Bloomfield, Conn., health insurer also recorded a $28-million charge in the 2011 quarter related to its acquisition of insurer HealthSpring Inc., a $3.8-billion deal it completed on Tuesday. Cigna earned $290 million, or $1.04 per share, in the three months that ended Dec. 31. That compares to $461 million, or $1.69 per share, in the 2010 quarter. Revenue climbed less than 1 percent to $5.46 billion.