AMN Healthcare Services Inc. (NYSE: AHS), the largest U.S. healthcare staffing firm, reported first-quarter revenue fell 4.5 percent year over year to $240.9 million, below the company’s guidance of $244 million to $248 million.

However, gross margin in the first quarter improved to 30.7 percent from 29.0 percent in the year-ago quarter. The company attributed the increase to gross margin improvement across all business segments, as well as the addition of the ShiftWise, a healthcare vendor management system acquired by AMN in November.

Locum tenens staffing revenue rose 2.2 percent on a year-over-year basis in the first quarter to $66.9 million.

Physician permanent placement revenue rose 6.7 percent in the first quarter to $10.6 million.

However, revenue in AMN’s nurse and allied healthcare staffing division — which includes Shiftwise and is the company’s largest segment — fell 7.5 percent in the first quarter to $163.5 million.

AMN’s first-quarter net income edged up 0.9 percent from the year-ago quarter to $7.6 million.

The company expects consolidated second-quarter revenue of $244 million to $248 million.

Shares were down 11.19 percent in early afternoon trading. The company had a market cap of $519.7 million.