Shares of Aspect Medical Systems ( ASPM) were among the worst-performing health-related stocks Wednesday, slumping 13% after the medical-device maker posted better-than-expected fourth-quarter results but issued a first-quarter earnings guidance that fell below Wall Street's forecast. The company's fourth-quarter earnings rose to $3.1 million, or 13 cents a share, from $955,000, or 5 cents a share, a year earlier. Sales grew to $21.6 million from $15.7 million. Analysts polled by Thomson First Call expected earnings of 11 cents a share and sales of $20.7 million. Looking ahead, Aspect Medical sees first-quarter earnings of 3 cents to 4 cents a share, or 11 cents to 12 cents a share excluding stock-based compensation costs. The company predicts sales of $21.5 million to $22.2 million. Analysts project earnings of 13 cents a share on sales of $21.8 million. Aspect Medical said that product launch and sales force expenses would have a modest impact on earnings during the first quarter. Shares were trading down $4.54 to $31.42. Cyberonics ( CYBX) fell 2% after the medical-device maker turned in third-quarter results that were well below expectations. For the quarter ended Jan. 27, the company posted a loss of $14.6 million, or 58 cents a share, on sales of $31.3 million. Analysts expected a smaller loss of 35 cents a share, with sales of $36.9 million. During the year-earlier quarter, the company had a loss of about $817,000, or 3 cents a share, on sales of $26.2 million. For the fourth quarter, Cyberonics forecast sales of $34 million, well below the $44.5 million that analysts had been projecting. Shares recently were trading down 60 cents to $27.63, after reaching a 52-week low of $24.55 earlier in the day. Shares of Pediatrix Medical Group ( PDX) rose 8% after the contract medical services provider posted fourth-quarter earnings that topped expectations. The company reported earnings of $15.9 million, or 65 cents a share, on sales of $177.7 million. Excluding items, the company earned $31.6 million, or $1.30 a share. Analysts expected earnings of $1.28 a share and sales of $181.3 million. During the year-earlier period, the company earned $25.8 million, or $1.10 a share, on sales of $161 million.