Unit of Analysis
The unit of analysis is the hospital stay rather than the patient. All stays have been weighted to produce national estimates.

Coding Diagnoses and Procedures
Diagnoses and procedures associated with an inpatient hospitalization can be defined using several different medical condition classification systems. The Clinical Classifications Software (CCS) was used predominantly within this report to identify specific diagnoses and procedures. CCS is based on the International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM), a uniform and standardized coding system containing over 13,600 diagnosis codes and 3,700 procedure codes. Each discharge record in the NIS is associated with one or more ICD-9-CM diagnosis code(s) and may contain one or more ICD-9-CM procedure code(s) if a procedure was performed during that hospitalization. Each hospital stay can have multiple CCS diagnoses and multiple CCS procedures.

In the CCS, ICD-9-CM codes are clustered into a smaller number of clinically meaningful categories that are sometimes more useful for presenting descriptive statistics than are individual ICD-9-CM codes. CCS codes are used extensively in this report to define groups of diagnoses and procedures for analysis. The CCS codes allow the reader to quickly and easily recognize patterns and trends in broad categories of hospital utilization. More information on CCS can be found online (http://www.hcup-us.ahrq.gov/toolssoftware/ccs/ccs.jsp). Specific CCS conditions or diagnoses can also be summarized into CCS body system or condition categories, which are broad groups of CCS conditions, such as Neoplasms, Mental Disorders, and Diseases of the Circulatory System.

Exhibit Diagnoses and Procedures
Throughout this report, combinations of diagnostic and procedure codes are used to isolate specific conditions or procedures. These codes are defined below by exhibit number.

SECTION 2 — INPATIENT HOSPITAL STAYS BY DIAGNOSIS

EXHIBIT 2.1

Reasons for hospital stays are based on principal diagnosis defined by the following Major Diagnostic Categories (MDC):

SECTION 4 — COSTS FOR INPATIENT HOSPITAL STAYS

EXHIBIT 4.5

See definition for MDCs under Exhibit 2.1.

SECTION 5 — WOMEN'S HEALTH

Maternal stays and stays for childbirth in this section occurred among females ages 15-44. Non-maternal female stays are hospital stays for females of all ages who are not pregnant or did not give birth.

EXHIBIT 5.1 and 5.6

Childbirth stays were defined using the following Diagnosis Related Groups (DRG) for 1997-2007:

Childbirth stays were defined using the following DRGs for 2008-2009:

Maternal stays were defined using the above listed DRG codes or the following CCS diagnosis codes:

Average cost per day was calculated by taking the average of the cost per day for each stay.

EXHIBIT 5.2

See definition for MDCs under Exhibit 2.1.

EXHIBIT 5.6

Childbirth and maternal stays were defined by the DRGs and CCS codes for 1997-2009 listed under Exhibit 5.1.

Perineal lacerations

Stays for vaginal deliveries with perineal lacerations were defined using DRGs 372-375 for 1997-2007 and DRGs 767,768, 774, and 775 for 2008-2009, with the following ICD-9 diagnosis codes:

Vaginal delivery with and without episiotomy

Stays for vaginal delivery with episiotomy were defined using DRGs 372-375 for 1997-2007 and DRGs 767,768, 774, and 775 for 2008-2009, with the following CCS procedure code:

Stays for vaginal delivery without episiotomy were defined using the above DRGs, but excluded CCS procedure code 133 (Episiotomy).

Vaginal delivery after induction of labor

Stays for vaginal delivery after induction of labor were defined using DRGs 372-375 for 1997-2007 and DRGs 767,768, 774, and 775 for 2008-2009, with the following ICD-9 procedure codes:

Cesarean section delivery after induction of labor

Stays for Cesarean section delivery after induction of labor were defined using DRGs 370 and 371 for 1997-2007 and DRGs 765 and 766 for 2008-2009, with the following ICD-9 procedure codes:

Vaginal delivery without a previous Cesarean section

Stays for vaginal delivery without a previous Cesarean section were defined using DRGs 372-375 for 1997-2007 and DRGs 767,768, 774, and 775 for 2008-2009, and excluded the following CCS diagnosis code:

First time Cesarean section

Stays for first time Cesarean section were defined using DRGs 370 and 371 for 1997-2007 and DRGs 765 and 766 for 2008-2009, or the following ICD-9 diagnosis codes:

And excluded the following ICD-9 diagnosis codes:

Repeat Cesarean section

Stays for repeat Cesarean section were defined using DRGs 370 and 371 for 1997-2007 and DRGs 765 and 766 for 2008-2009, with the following ICD-9 diagnosis codes:

Vaginal birth after Cesarean section

Stays for vaginal birth after Cesarean section were defined using DRGs 372-375 for 1997-2007 and DRGs 767,768, 774, and 775 for 2008-2009, with CCS diagnosis code 189 (Previous C-section).

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