Inclusion of non-viable neonates in the birth record and its impact on infant mortality rates in Shelby County, Tennessee, USA

Abstract

Rates of infant death are one of the most common indicators of a population's overall health status. Infant mortality rates (IMRs) are used to make broad inferences about the quality of health care, effects of health policies and even environmental quality. The purpose of our study was threefold: i) to examine the characteristics of births in the area in relation to gestational age and birthweight; ii) to estimate infant mortality using variable gestational age and/or birthweight criteria for live birth, and iii) to calculate proportional mortality ratios for each cause of death using variable gestational age and/or birthweight criteria for live birth. We conducted a retrospective analysis of all Shelby County resident-linked birth and infant death certificates during the years 1999 to 2004. Descriptive test statistics were used to examine infant mortality rates in relation to specific maternal and infant risk factors. Through careful examination of 1999-2004 resident-linked birth and infant death data sets, we observed a disproportionate number of non-viable live births (≤20 weeks gestation or ≤350 grams) in Shelby County. Issuance of birth certificates to these non-viable neonates is a factor that contributes to an inflated IMR. Our study demonstrates the complexity and the appropriateness of comparing infant mortality rates in smaller geographic units, given the unique characteristics of live births in Shelby County. The disproportionate number of pre-viable infants born in Shelby County greatly obfuscates neonatal mortality and de-emphasizes the importance of post-neonatal mortality.

Keywords: African-American neonates.; extreme prematurity; fetal death; infant mortality rates; viability.

Figure 1

Comparison of 2003–2004 distribution of births by gestational age in Shelby County, TN vs the U.S. The clinical estimate was used for gestational age for Shelby County births; for the national distribution the date of last menses estimation was used.

Figure 2

Comparison of 1999–2004 distribution of births by birthweight in Shelby County, TN vs the U.S.

Figure 3

Relative risk of infant death by birthweight for Shelby County vs the U.S. from 1999 to 2004.

Figure 4

Crude and birthweight-adjusted IMRs (1999–2004) in Shelby County, TN compared with U.S. IMRs (2004).

Figure 5

Overall and neonatal infant mortality rates (1999–2004) including all birth-weights and all birth-weights over 350 grams.

Figure 6

1999–2004 IMRs in Shelby County, TN, by variables gestational age and birthweight criteria.