Introduction

This concept provides background information, definitions and diagnostic codes for discriminating between pre-gestational diabetes and gestational diabetes .

Background

Reliance on the use of ICD 9-CM and ICD-10-CA codes for discrimination between pre-gestational and gestational diabetes is problematic in administrative data as not all diabetes diagnosed in pregnancy is gestational diabetes. Diagnosis of diabetes in pregnancy prior to 21 weeks’ gestation most likely represents undiagnosed pre-gestational diabetes, not gestational diabetes itself. This is important as the timing of hyperglycemia influences the fetal and maternal outcomes expected. This definition relies on the timing of diagnosis rather than the ICD-9-CM and ICD-10-CA code itself as diabetes first diagnosed in pregnancy is often termed and coded as gestational diabetes when it may not strictly be so. Gestational diabetes is a risk factor for subsequent type 2 diabetes and probably exists on a continuum in at risk individuals. Additionally the diagnosis of gestational diabetes is hampered in ICD-9-CM as the 4th digit is required to discriminate from other complications of pregnancy. Standards exist for administrative data diagnosis of types 1 and 2 diabetes but not for gestational diabetes.

Pre-Gestational Diabetes Definition

A woman is considered to have pre-gestational diabetes if at any time from 2 years before her pregnancy start date OR prior to 21 weeks’ gestation she had:


• One or more hospitalizations (from the Hospital Abstracts data) with a diagnosis of diabetes: ICD-9-CM codes 250, 648.0, 648.8; ICD-10-CA codes E10-E14, O24, P70.0, P70.1, R73.0 OR
  
• Two or more physician visits (from the Medical Services data) with a diagnosis of diabetes: ICD-9-CM code 250.
  
  NOTE: This is a modified National Diabetes Surveillance System (NDSS) - 2008 definition.

Determining if the maternal pre-gestational diabetes is Type 1 or Type 2

For those women identified as having pre-gestational diabetes, determine the pre-gestational diabetes type (Type 1 or Type 2), using the following process:

1. As reported in the Diabetes Education Resource for Children and Adolescents (DERCA) data .
   
2. Based on the woman’s first diabetes hospital code reported in the 2 year diabetes evaluation period.
   Type 1: if ICD-9-CM codes 250.x1, 250.x3; ICD-10-CA codes E10, O24.5, O24.0.
   Type 2: if ICD-9-CM codes 250.x0, 250.x2; ICD-10-CA codes E11, O24.6, O24.1.
   
3. Type 2: if the woman did not receive any diabetes drugs during her gestation period (using the Drug Program Information Network (DPIN) data).
   
4. Type 2: if the woman only received a non-insulin diabetes drug (i.e.: ATC = A10B) during her gestation period.

Gestational Diabetes Definition

A woman is considered to have gestational diabetes ONLY if she received a diabetes diagnosis at 21 weeks’ gestation or greater and she had NO PRIOR diagnosis for pre-gestational diabetes.


• One or more hospitalizations with a diagnosis of diabetes: ICD-9-CM codes 250, 648.0, 648.8; ICD-10-CA codes E10-E14, O24, P70.0, P70.1, R73.0 OR
  
• One or more physician visits with a diagnosis of diabetes: ICD-9-CM code 250

As an additional check for women diagnosed with gestational diabetes in the index pregnancy their record is searched for a previous pregnancy in the 2 year period prior to the pregnancy start date to determine if she had been assigned any of the following codes during the first 20 weeks’ gestation:


• One or more hospitalizations with a diagnosis of diabetes: ICD-9-CM codes 250, 648.0, 648.8; ICD-10-CA codes E10-E14, O24, P70.0, P70.1, R73.0 OR
  
• One of more physician visits with a diagnosis of diabetes: ICD-9-CM code 250

If so her current gestational diabetes status is set to "NO" and her pre-gestational diabetes status is set to "YES" for the index pregnancy.