Original Article
Increased risks of neonatal and postneonatal mortality associated with teenage pregnancy had different explanations

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Abstract

Objective

To determine the potential pathway of the association between teenage pregnancy and neonatal and postneonatal mortality.

Study Design and setting

We carried out a retrospective cohort study of 4,037,009 nulliparous pregnant women under 25 years old who had a live singleton birth during 1995 to 2000, based on linked birth and infant death data set of the United States.

Results

Teenage pregnancy (10–19 years old) was associated with increased neonatal mortality (odds ratio [OR]: 1.20, 95% confidence interval [CI] = 1.16–1.24) and postneonatal mortality (OR: 1.47, 95% CI = 1.41–1.54) after adjustment for potential confounders. With further adjustment for weight gain during pregnancy, teenage pregnancy was still associated with increased risk of neonatal (OR: 1.23, 95% CI = 1.19–1.28) and postneonatal mortality (OR: 1.48, 95% CI = 1.42–1.55). When adjustment was made for gestational age at birth, there was no association of teenage pregnancy with neonatal mortality (OR: 0.98, 95% CI = 0.95–1.02), whereas there was significant association with postneonatal mortality (OR: 1.40, 95% CI = 1.34–1.46).

Conclusion

The increased risk of neonatal death associated with teenage pregnancy is largely attributable to higher risk of preterm births, whereas increased postneonatal mortality is independent of the known confounders and gestational age at birth.

Introduction

The infant mortality rate in the United States for infants born to teenage mothers has remained persistently high despite widespread study of this phenomenon [1]. In 1999, the infant mortality for women under 20 years old was 10.3 deaths per 1,000 live births compared to 7.0 per 1,000 live births for all ages [2]. Although in the United States, teenage birth rate has declined substantially during the last decades, from 62.1 per 1,000 women in 1991 to 48.7 per 1,000 women in 2000 [3], it has remained at least five times higher than that of other developed countries [4]. Approximately one million teenagers become pregnant in the United States every year, with approximately 500,000 births occurring to school-age mothers, 11–19 years old [5]. Teenage pregnancy remains a significant social, economical, and health care problem in the United States [4], [5], [6].

Previous studies have explored the association between teenage pregnancy and early neonatal mortality [7], neonatal mortality [1], [6], [8], [9], [10], [11], postneonatal mortality [1], [8], [9], and infant mortality [6], [12], [13], [14], [15]. Preterm births, low birth weight, and low weight gain during pregnancy might be the intermediate variables in the association between teenage pregnancy and infant mortality. There were some controversies on whether these intermediate variables should be included in the multiple regression models. With control of educational level [7], [15], race [1], [6], economical status [1], [11], [14], marital status [1], [7], [15], parity [1], [7], [14], maternal prepregnancy height [14], smoking [1], [7], [14], [15] and alcohol use [1], [15] during pregnancy, birth defects [10], and adequacy of prenatal care [1], [7], [15] in their multivariate models, some studies have adjusted for gestational age [7], [9], [13], birth weight [7], [8], [13], and/or weight gain during pregnancy [7], [14], whereas other studies did not adjust for these last three variables [1], [6], [10], [11], [12], [15]. The inconsistent conclusions on the association between teenage pregnancy and infant mortality could be largely attributable to adjustment for the abovementioned three intermediate variables or not.

Young maternal age was probably a marker for one or more maternal risk factors to be associated with infant mortality rather than only an indication of maternal maturity [16]. Whether the observed association between teenage pregnancy and infant mortality simply reflects the deleterious sociodemographic environment that many pregnant teenagers confront or whether biological immaturity is also causally related remains controversial. Markovitz et al. [1] thought that socioeconomic factors might largely explain the increased risk of neonatal death among younger teenage mothers, but not the increase in postneonatal death. Reichmann and Pagnini [15] found that socioeconomic factors might account for some, but not all the effect of young maternal age on infant mortality. Mahfouz et al. [17] thought that pregnant teenagers were not a high-risk group, if good prenatal care was provided. However, Olausson et al. [9] believed that the increased risk of neonatal and postneonatal death among young teenagers might be related to biological immaturity. Friede et al. [8] further indicated that the increased risk of neonatal death could be explained by higher risk of low birth weight in infants born to teenage mothers; only part of the increased risk of postneonatal mortality was attributed to low birth weight. DuPlessis et al. [13] claimed that the incidence of infant mortality was unrelated to maternal age after controlling for prematurity and low birth weight.

Many previous epidemiologic studies were not designed to facilitate understanding the effect of maternal age on infant mortality. For example, some studies have been deliberately designed to eliminate variation of study subjects, such as institutional [10] or restricted in the identical race and ethnicity [8]. The results of some previous studies suggested that different factors were involved in the association between teenage pregnancy and neonatal and postneonatal mortality [8], [15], and studying infant mortality as a whole might obscure the association. The primary objective of this large population-based study was to explore whether teenage pregnancy was associated with an increased risk of neonatal death and postneonatal death independent of known confounders and what was the potential pathway for the observed association.

Section snippets

Study population

This study was based on the 1995–2000 nationally linked birth/infant death data set of the United States, compiled by National Center for Health Statistics, Centers for Disease Control and Prevention. The live births and infant deaths were registered in the 50 states and the District of Columbia. The data were precoded according to uniform specifications, and had gone through vigorous statistical quality checks by the National Center for Health Statistics [18]. Available information in this

Results

There were 23,654,785 live births in the linked 1995–2000 birth and infant death data set. Among them, 9.24% infants were born to mothers aged 20–24 years and 8.75% to women younger than 20 years. There were 0.85% infants born to younger teenage mothers aged 10–15 years, 3.02% to women aged 16–17 years, and 4.89% to women aged 18–19 years. In total, there were 4,254,752 first-born singleton infants whose mothers were younger than 25 years of age. The subjects with missing information on time of

Discussion

Our large population-based study indicated that teenage pregnancy carried an increased risk of neonatal and postneonatal death independent of potential confounding variables. The salient finding in this large population-based study was that the increased risk of neonatal death among infants born to teenage mothers was largely attributable to increased risk of preterm delivery in teenage mothers. By contrast, higher postneonatal mortality in teenage group was partly explained by gestational age

Acknowledgments

Dr. Chen is a recipient of Post-PhD fellowship from the CIHR/STIRRHS. Drs. Wen and Walker are recipients of New Investigator's Award from the CIHR.

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