Natus Medical Inc. developer and manufacturer of medical devices fore newborns said Tuesday it is planning to make a public offering of 3.5 million common shares.

The San Carlos, California-based group said late today it filed a preliminary prospectus supplement to its effective shelf registration statement related to the offer.

The company expects to grant a 30-day option to the underwriters to purchase up to an additional 15 percent of the shares to cover over-allotments according to a statement on the company's website.

The company said all of the shares are being sold by Natus Medical. They are being offered by Cowen and Company, LLC and UBS Investment Bank as joint bookrunning managers and Natixis Bleichroeder Inc., Needham & Company, LLC, Raymond James & Associates, Inc. and Roth Capital Partners, LLC are acting as co-managers, the company said in a press release.

Shares of Natus Medical rose 1.99 percent to close at $21.52 on the Nasdaq Stock Market.