1. This study was supported by grant T76-MC00011 from the Maternal and Child Health Bureau (Title V, Social Security Act), Health Resources and Services Administration, U.S. Department of Health and Human Services. Evidence of a Growth/Reproductive Trade-off in African-American Adolescent Gravidas Jane Rees, MS, RD, PhC Departments of Anthropology, Maternal & Child Health Program, School of Public Health and Community Medicine, University of Washington, Seattle, WA. Presented at the Annual Meeting of The Human Biology Association, Tempe, AZ. April, 2003.

2. 1. Introduction Life history theory predicts offspring of youngest mothers will be small, as result of a physiological growth/reproductive trade-off affecting recently fecund gravidas. 1,2 Some investigators 3,4,5 deny infants are affected by physical characteristics of adolescent pregnancies, asserting "a biological explanation seems unwarranted”, Geronimus (1986).

3. 2. Hypothesis Weight of first and subsequent births to African- Americans is associated with age of mother and thus with a potential growth/reproductive trade-off effect on size of infants born to mothers likely to be less than fully mature.

4. 3. Methods Retrospective cross sectional analysis of a population cohort. National Center for Health Statistics Linked Birth/Infant Death Data Set. 6 numerator - all 1999 US infant deaths linked to corresponding birth certificates. denominator - all 1999 US births. Data selection, filtering, tabulation, etc. - using SETS (Statistical Export & Tabulation System), provided with the data set. Finite population, almost no sampling error, differences essentially “significant”, confidence intervals developed. 586,000 singleton births to African-American mothers. 12-30 years with at least 100 births in index year. birth order from 1st to 21st birth.

5. 4. Results Mean weight of first births was positively associated with mothers' age from 12 years to 21 years, rising consistently from 2930 grams at 12 years to 3112 grams at 21 years. (Table 1)Table 1 Mean weight of births to mothers above age 21 years did not consistently increase with mothers' age, although for most ages above 22 years they were higher than 3112 grams. (Figures 1a and 1b)1a1b Mean weights of 2nd, 3rd and 4th births increased consistently with mothers' age until 29 years however, they were lower than mean weights of 1st births until ages 18, 20, and 21 years, respectively. (Figures 1a and 1b)1a1b Relationship between mothers' age and mean birth weight of 1st - 4th births to mothers at each age was unchanged by trimester of prenatal care initiation or marital status (1996-1999 mothers combined to obtain sufficient married adolescents for analysis). (Figure 2)Figure 2

6. 5. Conclusions As predicted by life history theory, infants of youngest African- American mothers in this national population were smallest, in association with mothers' age; the relationship was unchanged by trimester prenatal care initiated or marital status. Results suggest the pregnancies of young African-American mothers were physically affected by a growth/reproductive trade-off of substantial magnitude, sufficiently strong to overcome individual variation in the timing of pubertal development characteristic of this population. 7

7. 6. Implications Applying the concept of a physiological trade-off in studies of the specific metabolic processes allocating somatic resources between adolescent gravidas and their infants could lead to valuable insights. Short term, life course, 8 and intergenerational 9 outcome of adolescent pregnancy in human populations can be predicted and effectively tested by life history theory. The high frequency of 1st births to young mothers 16 - 22 years who produced the lightest infants should be a focus of concern. 10

8. References 1 Stearns SC. The evolution of life histories. New York, Oxford University Press 1992. 2 Hill K and Hurtado AM. Ache life history: the ecology and demography of a foraging people. New York, Aldine de Gruyter 1996. 3 Garn SM and Petzold AS. Characteristics of the mother and child in teenage pregnancy. Am J Dis Child 1983; 137: 365-368. 4 Geronimus, AT. The effects of race, residence, and prenatal care on the relationship of maternal age to neonatal mortality. AJ Pub Health 1986; 76: 1416-1421. 5 Stevens-Simon C and McAnarney ER. Adolescent maternal weight gain and low birth weight: a multifactorial model. Am J Clin Nutr 1988; 48: 948-953. 6 Center for Disease Control (CDC), National Center for Health Statistics. 1999 Perinatal Mortality Data File. CD-ROM Series 20 Number 20. 2002. 7 Herman-Giddens M, Slora E, Wasserman R, et al. Secondary sexual characteristics and menses in young girls seen in office practice: A study from the Pediatric Research in Office Settings Network. Pediatrics 1997; 4: 505-512. 8 Ben-Shlomo Y and Kuh D. A life course approach to chronic disease epidemiology: conceptual models, empirical challenges and interdisciplinary perspectives. Int J Epidemiol 2002; 31: 285-293. 9 Emanuel I. Intergenerational factors in pregnancy outcome: implication for teratology? In: Kalter, H (ed.). Issues and reviews in teratology, Vol. 6. New York, Plenum Press 1993. 10 American Academy of Pediatrics, Committee on Adolescence: Adolescent pregnancy current trends and issues: 1998. Pediatrics 1999; 103: 516-520.

9. Table 1

10. Figure 1a

11. Figure 1b

12. Figure 2