Teenage Pregnancy and Adverse Birth Outcomes: A Large Population Based Retrospective Cohort Study

Xi-Kuan Chen; Shi Wu Wen; Nathalie Fleming; Kitaw Demissie; George G Rhoads; Mark Walker


Int J Epidemiol. 2007;36(2):368-373. 

In This Article

Abstract and Introduction


Background: Whether the association between teenage pregnancy and adverse birth outcomes could be explained by deleterious social environment, inadequate prenatal care, or biological immaturity remains controversial. The objective of this study was to determine whether teenage pregnancy is associated with increased adverse birth outcomes independent of known confounding factors.
Methods: We carried out a retrospective cohort study of 3 886 364 nulliparous pregnant women <25 years of age with a live singleton birth during 1995 and 2000 in the United States.
Results: All teenage groups were associated with increased risks for pre-term delivery, low birth weight and neonatal mortality. Infants born to teenage mothers aged 17 or younger had a higher risk for low Apgar score at 5 min. Further adjustment for weight gain during pregnancy did not change the observed association. Restricting the analysis to white married mothers with age-appropriate education level, adequate prenatal care, without smoking and alcohol use during pregnancy yielded similar results.
Conclusions: Teenage pregnancy increases the risk of adverse birth outcomes that is independent of important known confounders. This finding challenges the accepted opinion that adverse birth outcome associated with teenage pregnancy is attributable to low socioeconomic status, inadequate prenatal care and inadequate weight gain during pregnancy.


Some important factors have strongly influenced the teenage pregnancy rate in recent decades.[1] The first factor is the declining age at menarche. Historical data from the United States and several European countries show a clear secular trend, with age at menarche declining at a rate of 2-3 months per decade since the 19th century, resulting in overall declines of about 3 years.[2] The decline in the age of menarche is attributed mostly to improved health and nutrition.[3] The second factor is that the first sexual activity is initiated at a much younger age. The youth risk behaviour study (YRBS) suggested that almost one-half of the United States high school students have had sexual intercourse in their lifetime, while ~7% initiated sexual intercourse before the age of 13 years.[4] The third factor is the low use rate of contraception. Although knowledge and use of contraception has been increasing globally, many teenagers have inadequate protection against pregnancy and contraception use among teenagers is still very low. For example, in 2005, only 51.8% teenagers consistently use contraception in Italy.[5] This may be related to less education awareness about contraception, and less access to contraceptives and emergency contraception. Approximately one million adolescents become pregnant in the United States every year, with ~500 000 births occurring to school age mothers with 11-19 years old.[6] Although recent USA data have shown a decrease in the proportion of teenage births over the last 10 years, teenage childbirth rate in the United States remained at least five times greater than that of other industrialized countries.[7] As a result, teenage pregnancy remains a significant social, economical and health care problem in the United States.[6,7,8]

Most studies from developed and developing countries have consistently reported that teenage pregnancy were at increased risk for pre-term delivery[8,9,10,11,12] and low birth weight (LBW)[8,10,11,13,14] although some studies failed to find such an association.[15,16,17] The relation between teenage pregnancy and small for gestational age (SGA) births in teenage mothers has been reported by some studies,[9,10,18,19] but not by others.[20,21] Some studies have found increased risk of neonatal mortality among infants born to teenage mothers,[8,20,21] whereas others found no increase.[14,18,19] Some adverse outcomes that might be associated with teenage pregnancy, such as low Apgar score and congenital malformations, should be further evaluated.

Young maternal age is probably a marker for one or more other maternal risk factors associated with adverse birth outcomes rather than only an indication of incomplete maternal growth.[22] Whether the observed association between teenage pregnancy and adverse birth outcomes simply reflects the deleterious sociodemographic environment that many pregnant teenagers confront or whether biological immaturity is also causally related remains controversial. Mahfouz et al.[23] thought that pregnant teenagers were not a high-risk group if good prenatal care was provided. Rogers and Yoder et al.[24,25] found that young maternal age was not an independent risk factor for adverse birth outcomes. The increased risk probably was attributable to other factors that were related to teenage pregnancy such as: black, unmarried, low socioeconomic status and inadequate prenatal care. Satin et al.[14] concluded that teenage pregnancies aged between 16 and 19 years had no risk for intrinsic maternal youth and the obstetric risk increased only in teenage <16 years of age, while Fraser et al.[9] suggested that young age conferred an increased risk of adverse pregnancy outcome, which was intrinsic to maternal youth.

Many previous studies in this area suffered from limited sample size and lack of information on confounders, and the study sample came from testing centers. Moreover, some studies were carried out during a long time period that might not reflect current health care practices. The objective of this large population based study was to determine whether teenage pregnancy was associated with increased risks of adverse birth outcomes independent of known confounders.


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