ANN ARBOR, Michigan (AP) — Domino’s Pizza Inc.’s first quarter earnings aren’t likely to calm investors’ concerns about slowing growth at the world’s biggest pizza chain.

The Ann Arbor-based company said Wednesday that sales at U.S. stores open at least a year rose 3.9% in the January-March period. That was down from 8.3% a year ago, and fell short of Wall Street’s forecast of 4.9%, according to analysts polled by FactSet.

International same-store sales rose 1.5%, down from 5% a year ago.

Domino’s has been expanding so it can deliver pizzas more quickly. But it’s facing a challenge from delivery services like GrubHub.

Domino’s first quarter net income rose 4.4% to $92.7 million, or $2.20 per share. That beat analysts’ forecast of $2.09. Revenue rose 6.4% to $836 million, which was short of expectations.