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