UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                  SCHEDULE 13D
                    Under the Securities Exchange Act of 1934
                               (Amendment No. 12)

                        NATUS MEDICAL INCORPORATED (BABY)
--------------------------------------------------------------------------------
                                (Name of Issuer)

                                  Common Stock
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                         (Title of Class of Securities)

                                    639050103
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                                 (CUSIP Number)

                                David Nierenberg
                               The D3 Family Funds
                               19605 NE 8th Street
                                 Camas, WA 98607
                                 (360) 604-8600

                                 With a copy to:

                               Henry Lesser, Esq.
                                DLA Piper US LLP
                             2000 University Avenue
                            East Palo Alto, CA 94303
                                 (650) 833-2000
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                  (Name, Address and Telephone Number of Person
                Authorized to Receive Notices and Communications)


                                 April 30, 2009
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             (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.
--------------------------------------------------------------------------------
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

                    0
               -----------------------------------------------------------------
  NUMBER OF    8    SHARED VOTING POWER
   SHARES
BENEFICIALLY        550,291 Common shares (2.0%)
  OWNED BY     -----------------------------------------------------------------
    EACH       9    SOLE DISPOSITIVE POWER
  REPORTING
   PERSON           0
    WITH       -----------------------------------------------------------------
               10   SHARED DISPOSITIVE POWER

                    550,291
--------------------------------------------------------------------------------
11   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

     For the reporting person listed on this page, 550,291; for all reporting
     persons as a group, 3,602,044 shares (12.9%)
--------------------------------------------------------------------------------
12   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES*  [_]


--------------------------------------------------------------------------------
13   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

     12.9%
--------------------------------------------------------------------------------
14   TYPE OF REPORTING PERSON*

     PN
--------------------------------------------------------------------------------
                     *SEE INSTRUCTIONS BEFORE FILLING OUT!


                                       2


--------------------------------------------------------------------------------
1    NAME OF REPORTING PERSON
     S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSON

     The D3 Family Bulldog Fund, L.P.
--------------------------------------------------------------------------------
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

                    0
               -----------------------------------------------------------------
  NUMBER OF    8    SHARED VOTING POWER
   SHARES
BENEFICIALLY        2,339,995 common shares (8.4%)
  OWNED BY     -----------------------------------------------------------------
    EACH       9    SOLE DISPOSITIVE POWER
  REPORTING
   PERSON           0
    WITH       -----------------------------------------------------------------
               10   SHARED DISPOSITIVE POWER

                    2,339,995
--------------------------------------------------------------------------------
11   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

     For the reporting person listed on this page, 2,339,995; for all reporting
     persons as a group, 3,602,044 shares (12.9%)
--------------------------------------------------------------------------------
12   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES*  [_]


--------------------------------------------------------------------------------
13   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

     12.9%
--------------------------------------------------------------------------------
14   TYPE OF REPORTING PERSON*

     PN
--------------------------------------------------------------------------------
                     *SEE INSTRUCTIONS BEFORE FILLING OUT!


                                       3


--------------------------------------------------------------------------------
1    NAME OF REPORTING PERSON
     S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSON

     The D3 Family Canadian Fund, L.P.
--------------------------------------------------------------------------------
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

                    0
               -----------------------------------------------------------------
  NUMBER OF    8    SHARED VOTING POWER
   SHARES
BENEFICIALLY        129,931 common shares (0.5%)
  OWNED BY     -----------------------------------------------------------------
    EACH       9    SOLE DISPOSITIVE POWER
  REPORTING
   PERSON           0
    WITH       -----------------------------------------------------------------
               10   SHARED DISPOSITIVE POWER

                    129,931
--------------------------------------------------------------------------------
11   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

     For the reporting person listed on this page, 129,931; for all reporting
     persons as a group, 3,602,044 shares (12.9%)
--------------------------------------------------------------------------------
12   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES*  [_]


--------------------------------------------------------------------------------
13   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

     12.9%
--------------------------------------------------------------------------------
14   TYPE OF REPORTING PERSON*

     PN
--------------------------------------------------------------------------------
                     *SEE INSTRUCTIONS BEFORE FILLING OUT!


                                       4


--------------------------------------------------------------------------------
1    NAME OF REPORTING PERSON
     S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSON

     The DIII Offshore Fund, L.P.
--------------------------------------------------------------------------------
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

     Bahamas
--------------------------------------------------------------------------------
               7    SOLE VOTING POWER

                    0
               -----------------------------------------------------------------
  NUMBER OF    8    SHARED VOTING POWER
   SHARES
BENEFICIALLY        581,827 common shares (2.1%)
  OWNED BY     -----------------------------------------------------------------
    EACH       9    SOLE DISPOSITIVE POWER
  REPORTING
   PERSON           0
    WITH       -----------------------------------------------------------------
               10   SHARED DISPOSITIVE POWER

                    581,827
--------------------------------------------------------------------------------
11   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

     For the reporting person listed on this page, 581,827; for all reporting
     persons as a group, 3,602,044 shares (12.9%)
--------------------------------------------------------------------------------
12   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES*  [_]


--------------------------------------------------------------------------------
13   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

     12.9%
--------------------------------------------------------------------------------
14   TYPE OF REPORTING PERSON*

     PN
--------------------------------------------------------------------------------
                     *SEE INSTRUCTIONS BEFORE FILLING OUT!


                                       5


--------------------------------------------------------------------------------
1    NAME OF REPORTING PERSON
     S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSON

     Nierenberg Investment Management Company, Inc.
--------------------------------------------------------------------------------
2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
                                                                 (a)  [X]
                                                                 (b)  [_]
--------------------------------------------------------------------------------
3    SEC USE ONLY


--------------------------------------------------------------------------------
4    SOURCE OF FUNDS*

     AF
--------------------------------------------------------------------------------
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

                    0
               -----------------------------------------------------------------
  NUMBER OF    8    SHARED VOTING POWER
   SHARES
BENEFICIALLY        3,602,044 shares (12.9%)
  OWNED BY     -----------------------------------------------------------------
    EACH       9    SOLE DISPOSITIVE POWER
  REPORTING
   PERSON           0
    WITH       -----------------------------------------------------------------
               10   SHARED DISPOSITIVE POWER

                    3,602,044 shares
--------------------------------------------------------------------------------
11   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

     For the reporting person listed on this page, 3,602,044; for all reporting
     persons as a group, 3,602,044 shares (12.9%)
--------------------------------------------------------------------------------
12   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES*  [_]


--------------------------------------------------------------------------------
13   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

     12.9%
--------------------------------------------------------------------------------
14   TYPE OF REPORTING PERSON*

     CO
--------------------------------------------------------------------------------
                     *SEE INSTRUCTIONS BEFORE FILLING OUT!


                                       6


--------------------------------------------------------------------------------
1    NAME OF REPORTING PERSON
     S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSON

     Nierenberg Investment Management Offshore, Inc.
--------------------------------------------------------------------------------
2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
                                                                 (a)  [X]
                                                                 (b)  [_]
--------------------------------------------------------------------------------
3    SEC USE ONLY


--------------------------------------------------------------------------------
4    SOURCE OF FUNDS*

     AF
--------------------------------------------------------------------------------
5    CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED
     PURSUANT TO ITEMS 2(d) OR 2(e)                                   [_]


--------------------------------------------------------------------------------
6    CITIZENSHIP OR PLACE OF ORGANIZATION

     Bahamas
--------------------------------------------------------------------------------
               7    SOLE VOTING POWER

                    0
               -----------------------------------------------------------------
  NUMBER OF    8    SHARED VOTING POWER
   SHARES
BENEFICIALLY        581,827 common shares (2.1%)
  OWNED BY     -----------------------------------------------------------------
    EACH       9    SOLE DISPOSITIVE POWER
  REPORTING
   PERSON           0
    WITH       -----------------------------------------------------------------
               10   SHARED DISPOSITIVE POWER

                    581,827 common shares
--------------------------------------------------------------------------------
11   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

     For the reporting person listed on this page, 581,827; for all reporting
     persons as a group, 3,602,044 shares (12.9%)
--------------------------------------------------------------------------------
12   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES*  [_]


--------------------------------------------------------------------------------
13   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

     12.9%
--------------------------------------------------------------------------------
14   TYPE OF REPORTING PERSON*

     CO
--------------------------------------------------------------------------------
                     *SEE INSTRUCTIONS BEFORE FILLING OUT!


                                       7


--------------------------------------------------------------------------------
1    NAME OF REPORTING PERSON
     S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSON

     David Nierenberg
--------------------------------------------------------------------------------
2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
                                                                 (a)  [X]
                                                                 (b)  [_]
--------------------------------------------------------------------------------
3    SEC USE ONLY


--------------------------------------------------------------------------------
4    SOURCE OF FUNDS*

     AF
--------------------------------------------------------------------------------
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

                    0
               -----------------------------------------------------------------
  NUMBER OF    8    SHARED VOTING POWER
   SHARES
BENEFICIALLY        3,602,044 common shares (12.9%)
  OWNED BY     -----------------------------------------------------------------
    EACH       9    SOLE DISPOSITIVE POWER
  REPORTING
   PERSON           0
    WITH       -----------------------------------------------------------------
               10   SHARED DISPOSITIVE POWER

                    3,602,044
--------------------------------------------------------------------------------
11   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

     For the reporting person listed on this page, 3,602,044; for all reporting
     persons as a group, 3,602,044 shares (12.9%)
--------------------------------------------------------------------------------
12   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES*  [_]


--------------------------------------------------------------------------------
13   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

     12.9%
--------------------------------------------------------------------------------
14   TYPE OF REPORTING PERSON*

     IN
--------------------------------------------------------------------------------
                     *SEE INSTRUCTIONS BEFORE FILLING OUT!


                                       8


      This Amendment No. 12 to Schedule 13D (this "Amendment") amends the
below-indicated Item from the Schedule 13D (the "Schedule 13D") previously filed
by or on behalf of the undersigned parties (the "Reporting Persons") by
supplementing such Item with the information below:

Item 5.  Interest in Securities of the Issuer.

      (a, b) The Reporting Persons, in the aggregate, beneficially own 3,602,044
Shares, constituting approximately 12.9% of the outstanding Shares.

      (c) During the past 60 days the following sales of Shares were made by the
Reporting Persons named below in open market transactions:

 Fund                        Transaction Date         Shares Sold          Price
 ----                        ----------------         -----------          -----
 DIII Offshore Fund, LP        03/16/2009                  18,100           7.73
 DIII Offshore Fund, LP        03/17/2009                  62,800           7.62
 DIII Offshore Fund, LP        03/18/2009                  69,100           8.11
 DIII Offshore Fund, LP        03/27/2009                  35,454           9.14
 D3 Family Fund, LP            03/31/2009                  18,000           8.69
 DIII Offshore Fund, LP        03/31/2009                  27,800           8.69
 D3 Family Fund, LP            04/30/2009                 134,000           8.90
 D3 Family Bulldog Fund, LP    04/30/2009                 230,000           8.90
 DIII Offshore Fund, LP        04/30/2009                 136,000           8.90


                                       9


                                    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.

                                       D3 Family Fund, L.P., D3 Bulldog Fund,
                                       L.P., and D3 Family Canadian Fund, L.P.

                                       By: Nierenberg Investment Management
                                            Company, Inc.


                                       Its: General Partner
May 1, 2009                            By: /s/ David Nierenberg
-------------------------              -----------------------------------------
                                             David Nierenberg, President


                                       DIII Offshore Fund, L.P.

                                       By: Nierenberg Investment Management
                                            Offshore, Inc.

                                       Its: General Partner


May 1, 2009                            By: /s/ David Nierenberg
-------------------------              -----------------------------------------
                                             David Nierenberg, President


                                       Nierenberg Investment Management
                                            Company, Inc.


May 1, 2009                            By: /s/ David Nierenberg
-------------------------              -----------------------------------------
                                             David Nierenberg, President


                                       Nierenberg Investment Management
                                            Offshore, Inc.


May 1, 2009                            By: /s/ David Nierenberg
-------------------------              -----------------------------------------
                                             David Nierenberg, President


May 1, 2009                            /s/ David Nierenberg
-------------------------              -----------------------------------------
                                             David Nierenberg


                                       10