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

In a surprising turn of events today, the Federal Reserve shocked Wall Street by voting against tapering its bond-buying program. With that news, the markets rallied and all three of the major indexes moved nearly 1% higher. The laggard was the Dow Jones Industrial Average (DJINDICES:^DJI), which rose a mere 0.95%, or 147 points, while the S&P 500 jumped the most at 1.22% and the Nasdaq climbed higher by 1.01%. The Dow set a new all-time intraday high at 15,709 and a new record closing high at 15,676.

As the markets moved higher, only one loser could be found within the Dow: UnitedHealth (NYSE:UNH), which lost 1.71%. The move comes at a critical time for the company as the Obamacare exchanges are set to open up for business on October 1 and at this time it's clear neither the company nor shareholders know how the exchanges are going to affect profits. UnitedHealth is up 34.66% year to date even after today's decline and while the Dow itself is only higher by 19.63%, it's likely that the recent declining share price is due to investor uncertainty about the future and pulling their money out before the exchanges open for business.

Outside the Dow, two of the other big losers of the day were also health insurance companies as Cigna (NYSE:CI) and WellPoint (NYSE:ANTM) also inched lower. Cigna lost 2.95% while WellPoint fell 4.4%. Again both companies have had great runs over the past 52 weeks as Cigna is up more than 77% and WellPoint has risen nearly 50%, which gives current shareholders a lot to lose in the last quarter of the year if the exchanges turn out to be bad for business.

Another possible loser to the exchanges could be Express Scripts (NASDAQ:ESRX), which lost 4.64%. As employees move to the exchanges for health-care coverage for their employees, Express Scripts may lose business. Walgreen has announced that it will offer 160,000 of its employees insurance through one of the exchanges and that's causing today's move. As more employers offer coverage, Express Scripts and other pharmacy benefit management companies could lose business.  

In spite of everything that happened today, investors must remember that they don't yet know how changes related to Obamacare will affect any of these businesses. With that said, if you're a shareholder, the best course of action is to sit tight until there is accurate information on which to base a buy or sell decision.

Fool contributor Matt Thalman has no position in any stocks mentioned. Check back Monday through Friday as Matt explains what caused the Dow's winners and losers of the day and every Saturday for a weekly recap. Follow Matt on Twitter @mthalman5513

The Motley Fool recommends UnitedHealth Group. It recommends and owns shares of Express Scripts and WellPoint. 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.