BALTIMORE, United States — Under Armour Inc., the second- largest U.S. athletic-apparel maker, declined in early trading after growth slowed last quarter, raising concerns that the company's torrid expansion is waning.

Revenue rose 30 percent to $937.9 million in the third quarter, the Baltimore-based company said today in a statement. While that exceeded the $927 million estimated by analysts, the growth rate was a deceleration from the first half of the year. Under Armour also signaled in its full-year forecast that growth would slow further in the fourth quarter.

The shares dropped as much as 5.7 percent to $62.30 in early trading. Through yesterday’s close, the stock had been up 51 percent this year.

Under Armour, led by Chief Executive Officer and founder Kevin Plank, has been seeking new avenues for growth after first gaining a reputation for football gear. That includes selling electronic fitness-tracking devices and trying to appeal to more women.

Net income rose 22 percent to $89.1 million, or 41 cents a share, from $72.8 million, or 34 cents, a year earlier. Analysts had projected 40 cents, the average of 29 estimates compiled by Bloomberg.

The company updated its 2014 forecast, predicting sales growth of 30 percent over 2013. That signals that the fourth- quarter sales will grow at slower rate than projected. Revenue had climbed at 36 percent in the first quarter and 34 percent in the second.

Operating income will be about 31 percent to $348 million this year, the company said.

By Matt Townsend; editor: Nick Turner.