Fitbit is having its worst day since last week's IPO

Fitbit shares fell more than 6% in morning trading on Wednesday.

This is the biggest one-day drop for the maker of fitness trackers which has been on the market for less than one week.

Last Thursday, Fitbit surged up to 52% at its public debut, from the initial public offering price of $20 per share.

The stock has gone as high as $40, and on Wednesday was trading near $35 per share.

The stock is up nearly 15% from its opening price of $30.40.

The Wall Street Journal's Corrie Driebusch points out that this is unusual - and impressive - for a company that made a splash this big at its public debut.

Driebusch wrote, "since 2010, of the 32 newly-listed companies that raised at least $200 million in their IPOs and popped at least 40% on their first day of trading, less than half-13, to be exact-remained above their first-day close by the end of their first week of trading."

Here's a chart showing how the stock has traded so far: