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.

1
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.
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.
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.

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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) 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) 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) 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)
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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.
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Table 1
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Figure 1a
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Figure 1b
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Figure 2