The Maturity and MaturitySpecific Mortality Subgroup

1
Stage 1 Hypotheses Assessment of Changes in
Maturity at Birth and Maturity-Specific Mortality
State Infant Mortality Toolkit

• The Maturity and Maturity-Specific Mortality
  Subgroup

2
Overview

• Among the proposed hypotheses to explain
  adverse tends in infant mortality rates were
  temporal changes in maturity distributions and
  maturity-specific mortality.
• The Maturity Subgroup was designated to explore
  this possibility and this is presentation
  highlights those efforts to date (7/05).

3
Data

• In order to explore proposed birth
  maturity-related hypotheses that might explain
  infant mortality trends and develop examples for
  the SIMC Toolkit, we selected the following NCHS
  datasets
• U.S. Live Birth Cohort Linked files for 1985-1988
  and 1995-2000
• U.S. Fetal Death files 1985-1989 and 1995-2000.

4
Data Selection

• For this presentation we used the following case
  selection criteria
• Live births (1985-1988 and 1995-2000) to U.S.
  resident mothers
• Fetal deaths were excluded.

5
Maturity Hypothesis for Trends in Infant Mortality

• Formal Hypothesis
• There is no association between the currently
  observed trends in infant mortality and any
  changes in the maturity at birth of infants as
  measured by birth weight, gestational age and
  fetal growth, e.g., small for gestational age.

6
Maturity Hypothesis for Trends in Infant Mortality

• Rationale
• One of the strongest predictors of infant death
  is the maturity of an infant at birth with
  infants at the extremes of maturity being at
  highest risk.
• As infant mortality trends may be driven by
  changes in the proportion of these high risk
  infants, the examination trends in birth weight
  gestational age distributions is indicated.

7
Maturity Hypothesis for Trends in Infant Mortality

• Possible Pathways
• Changes in proportion of high risk birth weight
  or gestational age infants, e.g., increase in
  very preterm or very low birth weight rates
• Changes in proportion of small-for-gestational
  age infants.

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Birth Weight Distribution Changes1985-88 to
1995-2000
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Birth Weight Distribution1985-88 1995-2000
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Birth Weight Categories1985-88 1995-2000
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Birth Weight Categories1985-88 1995-2000
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Changes in Birth Weight Categories by State
1985-1888 1995-2000
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Birth Weight DistributionComments

• Slight decrement in BW distribution between
  1985-88 and 1995-2000 with increases in lt500g,
  VLBW, and LBW rates, although macrosomic (4000g)
  birth rates have decreased.
• Similar trends evident in each target State.
• Evidence suggests there has been an increase in
  rate of births with birth weights at the lower
  extreme of the BW distribution.

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Gestational Age Distribution Changes1985-88 to
1995-2000
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Gestational Age Distribution1985-88 1995-2000
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Gestational Age Categories1985-88 and 1995-2000
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Changes in Gestational Age Categories by State
1985-1888 1995-2000
22
Gestational Age DistributionComments

• Slight decrement in gestational age (GA)
  distribution between 1985-88 and 1995-2000 with
  increases in preterm, very preterm and extremely
  preterm rates.
• Similar trends evident in each target State.
• Postterm rates have decreased.
• Evidence suggests there has been an increase in
  rate of births with gestational ages at the lower
  extreme of the GA distribution.

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Changes in Patternsof Fetal Growth1985-88 to
1995-2000
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Birth Weight for Gestational Age Categories
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Birth Weight for Gestational Age Categories
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Birth Weight for Gestational Age Category (SGA)
by State 1985-88, 1998-2000
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Fetal Growth PatternsComments

• Change in gestational age reporting between time
  periods made have altered shape of fetal growth
  patterns (note decline in both SGA and LGA).
• SGA rates have declined, driven by decrease for
  term SGA infants.
• Preterm SGA rates have increased.

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Temporal Change in Outcomes1985-88 (reference)
1995-2000
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Recent Trends in Birth Outcome Measures
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Maturity Mortality TrendsUSA
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Maturity Mortality TrendsDelaware
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Maturity Mortality TrendsHawaii
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Maturity Mortality TrendsLouisiana
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Maturity Mortality TrendsMissouri
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Maturity Mortality TrendsNorth Carolina
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Overall Changes in Maturity at DeliveryPreliminar
y Summary

• During the last period, preterm, VLBW and LBW
  rates rose while infant mortality rate continued
  to decline.
• While there is some evidence of a decrement in
  maturity at birth that could negatively influence
  infant mortality rates, improvement in infant
  mortality for the U.S. generally continued,
  suggesting that factors other than maturity at
  birth had a greater impact on infant mortality
  trends.

38
Suggested References

• Alexander GR, Allen MC. Conceptualization,
  measurement, and use of gestational age. I.
  Clinical and public health practice. J Perinatol
  1996 16(1) 53-59.
• Alexander GR, Slay M. Prematurity at birth
  Trends, racial disparities, and epidemiology.
  Mental Retard Develop Disabilities Res Reviews
  2002 8 215-220
• Blondel B, Kogan, MD, et al. The impact of the
  increasing number of multiple births on the rates
  of preterm birth and low birth weight An
  international study. Am J Public Health 2002
  921323-1330.
• Demissie K, Rhoads GG, et al. Trends in preterm
  birth and neonatal mortality among blacks and
  whites in the United States from 1989 to 1996.
  Am J Epid 2001 154307-315.
• Kramer MS. Intrauterine growth and gestational
  duration determinants. Pediatrics 1987 80
  502-11.
• McCormick MC. Significance of low birth weight
  for infant mortality and morbidity. Birth Defects
  Orig Artic Ser 1988243-10.
• Oken E, Kleinman KP, et al. A nearly continuous
  measure of birth weight for gestational age using
  a United States national reference. BMC Pediatr
  2003 36.
• Wilcox LS, Marks JS, eds. From Data to Action.
  Atlanta Centers for Disease Control, 1994, pp
  163-178.

39
Maturity Specific Mortality Hypothesis for Trends
in Infant Mortality

• Formal Hypothesis
• There is no association between the currently
  observed trends in infant mortality and any
  changes in mortality risk for specific maturity
  at birth categories, as measured by birth weight,
  gestational age and fetal growth, e.g., small for
  gestational age

40
Maturity Hypothesis for Trends in Infant Mortality

• Rationale
• Overall infant mortality trends may be driven by
  changes in the risk of mortality for specific
  maturity at birth groups, e.g., increases in the
  survival of VLBW infants may have a marked effect
  on overall infant mortality rates.
• Therefore, trends in birth weight/gestational age
  specific infant mortality rates should be
  examined.

41
Maturity Specific Mortality Hypothesis for Trends
in Infant Mortality

• Possible Pathways
• Changes in birth weight or gestational
  age-specific survival, e.g., no temporal
  improvement in survival for lt1000 gram or lt24
  week infants
• Changes in survival of small-for-gestational age
  infants.

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Infant Mortality Indices 1985-88 1995-2000
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Gestational Age Specific Mortality1985-1988
1995-2000
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Fetal Growth Specific Infant Mortality1985-1988
1995-2000
47
Recent Trends in Birth Outcome Measures
48
Maturity Mortality TrendsUSA
49
Birth Weight Specific Infant MortalityTrends
Delaware 1995-2000
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Maturity Mortality TrendsDelaware
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Birth Weight Specific Infant Mortality Trends
Hawaii 1995-2000
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Maturity Mortality TrendsHawaii
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Birth Weight Specific Infant MortalityTrends
Louisiana 1995-2000
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Maturity Mortality TrendsLouisiana
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Birth Weight Specific Infant MortalityTrends
Missouri 1995-2000
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Maturity Mortality TrendsMissouri
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Birth Weight Specific Infant MortalityTrends
North Carolina 1995-2000
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Maturity Mortality TrendsNorth Carolina
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Summary

• Both birth weight and gestational age specific
  mortality have improved nationwide, although such
  recent trends are not evident in every State,
  e.g., Hawaii.
• These data suggest that the investigation of
  maturity-specific mortality is a viable
  hypothesis to explore for better understanding
  trends in infant mortality.

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Next Steps

• Use Kitagawa technique to explore contribution of
  changes in maturity and maturity-specific
  mortality to understand trends in infant
  mortality.
• Further examine the extent to which improvement
  in fetal growth patterns are negated by
  decrements in preterm birth rates.

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Next Steps

• Integrate findings of data reporting subgroup
  regarding changes in the measurement of
  gestational age and the reporting of lt500 g
  infants/fetal deaths.
• Repeat analyses with fetal death
• Explore impact of multiple births.

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Suggested References

• Alexander, GR, Kogan M, et al. U.S. birth
  weight-gestational age-specific neonatal
  mortality 1995-7 rates for Whites, Hispanics and
  African-Americans. Pediatrics 2003 111(1)
  e61-66.
• Alexander GR, Tompkins ME, at el. Trends and
  racial differences in birth weight and related
  survival. MCHJ 1999 3(1) 71-79.
• Allen MC, Alexander GR, et al. Racial differences
  in temporal changes in newborn viability and
  survival by gestational age. Paediatr Perinat
  Epid 2000 14(2) 152-158.
• Kleinman JC, Kovar MG, et al. A comparison of
  1960 and 1973-4 early neonatal mortality in
  selected states. Am J Epid 1978 108 454-469.
• Lee KS, Paneth N, et al. Neonatal mortality an
  analysis of the recent improvement in the United
  States. Am J Public Health 1980 7015-21.
• Lee KS, Paneth N, et al. The very
  low-birth-weight rate Principal predictor of
  neonatal mortality in industrialized populations.
  J Pediatr 1980 97759-64.
• Lee KS, Khoshnood B, et al. Which birth weight
  groups contributed most to the overall reduction
  in the neonatal mortality rate in the United
  States from 1960 to 1986? Paediatr Perinat Epid
  1995 9420-30.
• Sappenfield WM, Buehler JW, et al. Differences in
  neonatal and postneonatal mortality by race,
  birth weight, and gestational age. Public Health
  Rep. 1987 102(2) 182-192.