Indianapolis - Aetna Inc. officially reported that its fourth-quarter earnings for the past year plunged by 15% as the company continued to struggle with rapidly rising medical costs that effectively managed to hurt performance all throughout 2009.

On Friday, the Hartford, Conn. based health insurer revealed that medical costs, which are the company's largest expense, hiked by 14% to $6.1 Billion in the three months up-to December 31. The hurt through this, however, was somewhat offset by a 9% rise in premiums.

"To date, we have re-priced a significant portion of our commercial insured business and are creating momentum toward the improvement of our long-term operating margin profile", said Chief Executive Ronald A. Williams. During the fourth-quarter, Aetna managed to earn $165.9 Million, or 38 cents per share, a substantial fall from the earnings of $194.7 Million, or 42 cents, posted for the same period for the previous year.

Revenue, on the other hand, managed to rise by 13% to $8.76 Billion.