U.S. stock index futures added to losses on Thursday after disappointing readings on economic growth and the labor market.

First-quarter gross domestic product rose 1.8 percent, less robust growth than forecast, while jobless claims unexpectedly rose in the latest week.

S&P 500 futures fell 3.9 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures fell 21 points and Nasdaq 100 futures lost 5.5 points.

(Reporting by Ryan Vlastelica)