UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13D/A Under the Securities Act of 1934 (Amendment No. 6) Natus Medical Incorporated (BABY) (Name of Issuer) Common Stock (Title of Class of Securities) 639050103 (CUSIP Number) David Nierenberg The D3 Family Funds 19605 NE 8th Street Camas, WA 98607 360-604-8600 (Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications) February 7, 2005 (Date of Event which Requires Filing of this Statement) If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D and is filing this schedule because of ss.ss.240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box: |_| -------------------------------------------------------------------------------- 1 NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSON The D3 Family Fund, L.P. (David Nierenberg is president of the General Partner, which is Nierenberg Investment Management Company.) -------------------------------------------------------------------------------- 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) |X| (b) |_| -------------------------------------------------------------------------------- 3 SEC USE ONLY -------------------------------------------------------------------------------- 4 SOURCE OF FUNDS WC -------------------------------------------------------------------------------- 5 CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e) |_| -------------------------------------------------------------------------------- 6 CITIZENSHIP OR PLACE OF ORGANIZATION Washington -------------------------------------------------------------------------------- 7 SOLE VOTING POWER 1,427,022 common shares (8.4%) ----------------------------------------------------------------- NUMBER OF 8 SHARED VOTING POWER SHARES BENEFICIALLY 0 OWNED BY ----------------------------------------------------------------- EACH 9 SOLE DISPOSITIVE POWER REPORTING PERSON 1,427,022 WITH ----------------------------------------------------------------- 10 SHARED DISPOSITIVE POWER 0 -------------------------------------------------------------------------------- 11 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 2,558,514 shares (15.0%) -------------------------------------------------------------------------------- 12 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES |_| -------------------------------------------------------------------------------- 13 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 15.0% -------------------------------------------------------------------------------- 14 TYPE OF REPORTING PERSON PN -------------------------------------------------------------------------------- 2 -------------------------------------------------------------------------------- 1 NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSON The D3 Family Retirement Fund, L.P. (David Nierenberg is president of the General Partner, which is Nierenberg Investment Management Company.) -------------------------------------------------------------------------------- 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) |X| (b) |_| -------------------------------------------------------------------------------- 3 SEC USE ONLY -------------------------------------------------------------------------------- 4 SOURCE OF FUNDS WC -------------------------------------------------------------------------------- 5 CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e) |_| -------------------------------------------------------------------------------- 6 CITIZENSHIP OR PLACE OF ORGANIZATION Washington -------------------------------------------------------------------------------- 7 SOLE VOTING POWER 473,940 common shares (2.8%) ----------------------------------------------------------------- NUMBER OF 8 SHARED VOTING POWER SHARES BENEFICIALLY 0 OWNED BY ----------------------------------------------------------------- EACH 9 SOLE DISPOSITIVE POWER REPORTING PERSON 473,940 WITH ----------------------------------------------------------------- 10 SHARED DISPOSITIVE POWER 0 -------------------------------------------------------------------------------- 11 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 2,558,514 shares (15.0%) -------------------------------------------------------------------------------- 12 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES |_| -------------------------------------------------------------------------------- 13 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 15.0% -------------------------------------------------------------------------------- 14 TYPE OF REPORTING PERSON PN -------------------------------------------------------------------------------- 3 -------------------------------------------------------------------------------- 1 NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSON The D3 Children's Fund, L.P. (David Nierenberg is president of the General Partner, which is Nierenberg Investment Management Company.) -------------------------------------------------------------------------------- 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) |X| (b) |_| -------------------------------------------------------------------------------- 3 SEC USE ONLY -------------------------------------------------------------------------------- 4 SOURCE OF FUNDS WC -------------------------------------------------------------------------------- 5 CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e) |_| -------------------------------------------------------------------------------- 6 CITIZENSHIP OR PLACE OF ORGANIZATION Washington -------------------------------------------------------------------------------- 7 SOLE VOTING POWER 88,661 common shares (0.5%) ----------------------------------------------------------------- NUMBER OF 8 SHARED VOTING POWER SHARES BENEFICIALLY 0 OWNED BY ----------------------------------------------------------------- EACH 9 SOLE DISPOSITIVE POWER REPORTING PERSON 88,661 WITH ----------------------------------------------------------------- 10 SHARED DISPOSITIVE POWER 0 -------------------------------------------------------------------------------- 11 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 2,558,514 shares (15.0%) -------------------------------------------------------------------------------- 12 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES |_| -------------------------------------------------------------------------------- 13 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 15.0% -------------------------------------------------------------------------------- 14 TYPE OF REPORTING PERSON PN -------------------------------------------------------------------------------- 4 -------------------------------------------------------------------------------- 1 NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSON The D3 Offshore Fund, L.P. (David Nierenberg is president of the General Partner, which is Nierenberg Investment Management Company.) -------------------------------------------------------------------------------- 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) |X| (b) |_| -------------------------------------------------------------------------------- 3 SEC USE ONLY -------------------------------------------------------------------------------- 4 SOURCE OF FUNDS WC -------------------------------------------------------------------------------- 5 CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e) |_| -------------------------------------------------------------------------------- 6 CITIZENSHIP OR PLACE OF ORGANIZATION Washington -------------------------------------------------------------------------------- 7 SOLE VOTING POWER 300,658 common shares (1.8%) ----------------------------------------------------------------- NUMBER OF 8 SHARED VOTING POWER SHARES BENEFICIALLY 0 OWNED BY ----------------------------------------------------------------- EACH 9 SOLE DISPOSITIVE POWER REPORTING PERSON 300,658 WITH ----------------------------------------------------------------- 10 SHARED DISPOSITIVE POWER 0 -------------------------------------------------------------------------------- 11 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 2,558,514 shares (15.0%) -------------------------------------------------------------------------------- 12 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES |_| -------------------------------------------------------------------------------- 13 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 15.0% -------------------------------------------------------------------------------- 14 TYPE OF REPORTING PERSON PN -------------------------------------------------------------------------------- 5 -------------------------------------------------------------------------------- 1 NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSON The D3 Family Bulldog Fund, L.P. (David Nierenberg is president of the General Partner, which is Nierenberg Investment Management Company.) -------------------------------------------------------------------------------- 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) |X| (b) |_| -------------------------------------------------------------------------------- 3 SEC USE ONLY -------------------------------------------------------------------------------- 4 SOURCE OF FUNDS WC -------------------------------------------------------------------------------- 5 CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e) |_| -------------------------------------------------------------------------------- 6 CITIZENSHIP OR PLACE OF ORGANIZATION Washington -------------------------------------------------------------------------------- 7 SOLE VOTING POWER 268,233 common shares (1.6%) ----------------------------------------------------------------- NUMBER OF 8 SHARED VOTING POWER SHARES BENEFICIALLY 0 OWNED BY ----------------------------------------------------------------- EACH 9 SOLE DISPOSITIVE POWER REPORTING PERSON 268,233 WITH ----------------------------------------------------------------- 10 SHARED DISPOSITIVE POWER 0 -------------------------------------------------------------------------------- 11 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 2,558,514 shares (15.0%) -------------------------------------------------------------------------------- 12 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES |_| -------------------------------------------------------------------------------- 13 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 15.0% -------------------------------------------------------------------------------- 14 TYPE OF REPORTING PERSON PN -------------------------------------------------------------------------------- 6 Item 1. Security and Issuer. Common stock of Natus Medical Incorporated, 1501 Industrial Road, San Carlos. CA 94070 Item 2. Identity and Background. The D3 Family Fund, L.P. is a Washington State limited partnership, whose principal business is investing in the equities of public micro-cap issuers. Located at 19605 N.E. 8th St., Camas, Washington 98607. No convictions or administrative proceedings as described in 2 (d) and (e). Item 3. Source and Amount of Funds or Other Consideration Source of funds is money invested in the partnership by its partners. Item 4. Purpose of Transaction We mentioned in our December 6, 2004, 13D filing that we would happily buy more shares of BABY if we could do so without triggering the poison pill. On Friday, February 4th, we called Jim Hawkins, the CEO, with a request that he and the other members of the Board of Directors consider allowing us to purchase up to 20% of the company, without triggering the pill. Item 5. Interest in Securities of the Issuer. (a,b) D3 Family Fund, L.P. owns and has sole voting and dispositive power over 1,427,022 common shares of BABY. (c) N/A (d) N/A (e) N/A Item 6. Contracts, Arrangements, Understandings or Relationships with Respect to Securities of the Issuer. N/A Item 7. Material to be Filed as Exhibits N/A 7 SIGNATURE After reasonable inquiry and to the best of my knowledge and belief, each of the undersigned certifies that the information set forth in the Statement is true, complete and correct. February 7, 2005 /s/ DAVID NIERENBERG ---------------- ----------------------------------------- President Nierenberg Investment Management Company, Inc., the General Partner of The D3 Family Fund, L.P. 8 Item 1. Security and Issuer. Common stock of Natus Medical Incorporated, 1501 Industrial Road, San Carlos. CA 94070 Item 2. Identity and Background. The D3 Family Retirement Fund, L.P. is a Washington State limited partnership, whose principal Business is investing in the equities of public micro-cap issuers. Located at 19605 N.E. 8th St., Camas, Washington 98607. No convictions or administrative proceedings as described in 2 (d) and (e). Item 3. Source and Amount of Funds or Other Consideration Source of funds is money invested in the partnership by its partners. Item 4. Purpose of Transaction We mentioned in our December 6, 2004, 13D filing that we would happily buy more shares of BABY if we could do so without triggering the poison pill. On Friday, February 4th, we called Jim Hawkins, the CEO, with a request that he and the other members of the Board of Directors consider allowing us to purchase up to 20% of the company, without triggering the pill. Item 5. Interest in Securities of the Issuer. (a,b) The D3 Family Retirement Fund, L.P. owns and has sole voting and dispositive power over 473,940 common shares of BABY. (c) N/A (d) N/A (e) N/A Item 6. Contracts, Arrangements, Understandings or Relationships with Respect to Securities of the Issuer. N/A Item 7. Material to be Filed as Exhibits N/A 9 Signature After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct. February 7, 2005 /s/ DAVID NIERENBERG -------------------- ----------------------------------------- Date David Nierenberg President Nierenberg Investment Management Company, Inc., the General Partner of the D3 Family Retirement Fund, L.P. 10 Item 1. Security and Issuer. Common stock of Natus Medical Incorporated, 1501 Industrial Road, San Carlos. CA 94070 Item 2. Identity and Background. The D3 Children's Fund, L.P. is a Washington State limited partnership, whose principal business is investing in the equities of public micro-cap issuers. Located at 19605 N.E. 8th St., Camas, Washington 98607. No convictions or administrative proceedings as described in 2 (d) and (e). Item 3. Source and Amount of Funds or Other Consideration Source of funds is money invested in the partnership by its partners. Item 4. Purpose of Transaction We mentioned in our December 6, 2004, 13D filing that we would happily buy more shares of BABY if we could do so without triggering the poison pill. On Friday, February 4th, we called Jim Hawkins, the CEO, with a request that he and the other members of the Board of Directors consider allowing us to purchase up to 20% of the company, without triggering the pill. Item 5. Interest in Securities of the Issuer. (a,b) The D3 Children's Fund, L.P. owns and has sole voting and dispositive power over 88,661 common shares of BABY. (c) N/A (d) N/A (e) N/A Item 6. Contracts, Arrangements, Understandings or Relationships with Respect to Securities of the Issuer. N/A Item 7. Material to be Filed as Exhibits N/A 11 Signature After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct. February 7, 2005 /s/ DAVID NIERENBERG -------------------- ----------------------------------------- Date David Nierenberg President Nierenberg Investment Management Company, Inc., the General Partner of the D3 Children's Fund L.P. 12 Item 1. Security and Issuer. Common stock of Natus Medical Incorporated, 1501 Industrial Road, San Carlos. CA 94070 Item 2. Identity and Background. The D3 Offshore Fund, L.P. is a Washington State limited partnership, whose principal Business is investing in the equities of public micro-cap issuers. Located at 19605 N.E. 8th St., Camas, Washington 98607. No convictions or administrative proceedings as described in 2 (d) and (e). Item 3. Source and Amount of Funds or Other Consideration Source of funds is money invested in the partnership by its partners. Item 4. Purpose of Transaction We mentioned in our December 6, 2004, 13D filing that we would happily buy more shares of BABY if we could do so without triggering the poison pill. On Friday, February 4th, we called Jim Hawkins, the CEO, with a request that he and the other members of the Board of Directors consider allowing us to purchase up to 20% of the company, without triggering the pill. Item 5. Interest in Securities of the Issuer. (a,b) The D3 Offshore Fund, L.P. owns and has sole voting and dispositive power over 300,658 common shares of BABY. (c) N/A (d) N/A (e) N/A Item 6. Contracts, Arrangements, Understandings or Relationships with Respect to Securities of the Issuer. N/A Item 7. Material to be Filed as Exhibits N/A 13 Signature After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct. February 7, 2005 /s/ DAVID NIERENBERG -------------------- ----------------------------------------- Date David Nierenberg President Nierenberg Investment Management Company, Inc., the General Partner of the D3 Offshore Fund, L.P. 14 Item 1. Security and Issuer. Common stock of Natus Medical Incorporated, 1501 Industrial Road, San Carlos. CA 94070 Item 2. Identity and Background. The D3 Family Bulldog Fund, L.P. is a Washington State limited partnership, whose principal Business is investing in the equities of public micro-cap issuers. Located at 19605 N.E. 8th St., Camas, Washington 98607. No convictions or administrative proceedings as described in 2 (d) and (e). Item 3. Source and Amount of Funds or Other Consideration Source of funds is money invested in the partnership by its partners. Item 4. Purpose of Transaction We mentioned in our December 6, 2004, 13D filing that we would happily buy more shares of BABY if we could do so without triggering the poison pill. On Friday, February 4th, we called Jim Hawkins, the CEO, with a request that he and the other members of the Board of Directors consider allowing us to purchase up to 20% of the company, without triggering the pill. Item 5. Interest in Securities of the Issuer. (a,b) The D3 Family Bulldog Fund, L.P. owns and has sole voting and dispositive power over 268,233 common shares of BABY. (c) N/A (d) N/A (e) N/A Item 6. Contracts, Arrangements, Understandings or Relationships with Respect to Securities of the Issuer. N/A Item 7. Material to be Filed as Exhibits N/A 15 Signature After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct. February 7, 2005 /s/ DAVID NIERENBERG -------------------- ----------------------------------------- Date David Nierenberg President Nierenberg Investment Management Company, Inc., the General Partner of the D3 Family Bulldog Fund, L.P. 16