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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This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.