Stock index futures fell on Wednesday as Europe's debt crisis continued to worry investors and closely watched Italian bond yields rose again.

S&P 500 futures fell 12.1 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration of the contract. Dow Jones industrial average futures slid 86 points, and Nasdaq 100 futures lost 14.75 points.

( editing by W Simon )