Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Cigna Corporation (NYSE:CI) have lost 10% of their value today after the health insurer disappointed Wall Street with its fourth-quarter earnings report.

So what: Cigna's fourth-quarter revenue came in at $8.15 billion, a 7% year-over-year improvement and better than the $8.05 billion Wall Street consensus. However, Cigna's adjusted earnings of $1.39 per share were worse than the $1.49 in EPS analysts had expected (GAAP EPS was $1.29), and the company's guidance for 2014 now looks worse: While analysts had modeled Cigna's full-year EPS at $7.32, the company offered a range of $6.80 to $7.20 per share.

Now what: Obamacare's impact has yet to be fully felt on the health insurance industry's bottom line, but if this report is any indication, that impact won't be a good one. Shares of other insurers are also feeling the pain today as investors come to grips with the likelihood of higher medical costs -- Cigna highlighted higher-than-expected costs in its private Medicare business as a reason for the profit drag.

Today's drop shouldn't scare long-term investors away, but there might be better insurers out there for your investment dollars. Don't jump in before you assess Cigna's value relative to its peers.

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Alex Planes has no position in any stocks mentioned, and neither does The Motley Fool. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.