U.S. stock index futures pointed to a higher open on Wednesday as traders digested prepared remarks from the top-ranking Federal Reserve official.

Federal Reserve Chair Janet Yellen said the central bank is likely to reduce stimulus later this year. The Fed accumulated its $4.5 trillion balance sheet as it sought to stimulate the economy during and after the financial crisis. The expansion came largely through the purchase of Treasurys and mortgage-backed securities.

She also said the balance sheet reduction and rate increases would be gradual. Yellen also noted rates won't have to rise as much to get to neutral, as in previous decades.

Yellen will deliver her remarks in front of Congress later on Wednesday.

Stock futures jumped after the remarks were released. Dow futures traded 105 points higher, while S&P and Nasdaq futures climbed 11.25 points and 42.75 points, respectively.

On the earnings front, Bank of the Ozarks and Fastenal posted quarterly results before the bell. Barnes & Noble and MSC Industrial are both due to report after the market close.

In Europe, the pan-European Stoxx-600 index was around 0.9 percent higher on Wednesday. In Asia, the Shanghai composite in China closed 0.16 percent lower, while the Nikkei in Japan closed 0.48 percent lower.

In oil markets, Brent crude traded at around $48.27 a barrel on Tuesday, up 1.6 percent, while U.S. crude was around $45.89 a barrel, up 1.9 percent.

In the U.S. on Tuesday, stocks went on a wild ride as traders debated the impact of emails released by Donald Trump Jr.