BERLIN, Germany — Zalando, Europe's biggest dedicated online fashion retailer, said the launch of a new sports label by Beyonce had boosted sales since the Easter holidays after revenue grew less rapidly than expected in the first quarter.

Analysts have become accustomed to Zalando beating their expectations, with revenue having increased by a third in 2015. But the fashion sector got off to a slower start this year due to an earlier Easter and a cool early spring.

Zalando said first-quarter sales rose around 23-25 percent to 788 to 801 million euros, missing consensus for 822 million euros ($931 million).

Zalando's shares were down 1.7 percent at 0850 GMT, compared to a 1.4 percent firmer European retail sector. The stock is now trading at 55 times forward earnings, a high figure but a discount to Britain's ASOS which is on 57 times.

Launched in Berlin in 2008, Zalando serves customers in 15 European markets with more than 1,500 brands, including big names such as Gap, Banana Republic and Topshop.

Rival ASOS, recovering from a tough 2014 when it issued three profit warnings and suffered a warehouse fire, has seen its shares rise 13 percent this year, buoyed by stronger-than-expected sales for the first half to Feb. 29.

"A solid update, certainly not smashing out of the park a la ASOS," said Jefferies analyst David Reynolds, noting that Zalando is still outpacing ASOS in Europe, estimating the British firm grew just 15 percent in January and February.

Zalando management board member Rubin Ritter said Easter was usually slower as people were on holiday, but sales had picked up again since then, helped by heavy marketing for the launch of a new sports label, Ivy Park, co-founded by pop star Beyonce.

"We are positive for the season but you have to take the weeks and seasonality as it comes," he told Reuters.

Adjusted earnings before interest and tax (EBIT) came to between 12 and 28 million euros, compared with consensus for 21.6 million, while the adjusted EBIT margin should be 1.5 to 3.5 percent. Zalando reports full quarterly figures on May 12.

Zalando reiterated full-year guidance for revenue growth at the upper end of a 20 to 25 percent range and an adjusted EBIT margin of 3.0 to 4.5 percent. ($1 = 0.8830 euros)

By Emma Thomasson; editors: Maria Sheahan and Keith Weir.