General Obstetrics and Gynecology: Obstetrics
Fetal growth risk curves: Defining levels of fetal growth restriction by neonatal death risk

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Objective

We developed a fetal growth risk curve that delineates the birth weight values for gestational age that reflect a 2-, 2.5-, and 3-fold neonatal death risk relative to infants with normal fetal growth.

Study design

We analyzed 18,085,052 single gestation infants (25-42 weeks) who were born to US resident mothers from 1996 to 2000. Multivariate models were used to predict the relationship between neonatal death and birth weight percentile. Fetal risk curves were derived on the basis of birth weight percentile–specific neonatal mortality rates that were relative to an average rate of neonatal death for a comparison group that was representative of typical growth (ie, infants between 45th-55th birth weight percentiles for gestational age).

Results

The 10th percentile of birth weight for gestational age is associated with an increased but variable risk of neonatal death relative to the comparison group across the spectrum of gestational ages. At 26 weeks of gestation, infants at the 10th percentile experienced a 3-fold risk of dying within the first 28 days of life (relative to the comparison group); whereas at 40 weeks, the risk was 1.13.

Conclusion

Fetal growth risk curves facilitate the identification of populations of infants whose risk of death are deemed excessive compared with that of infants at the norm of fetal growth and may be useful for counseling pregnant women.

Section snippets

Material and methods

The data for this study were derived from the National Center for Health Statistics linked live birth/infant death cohort files. The project was reviewed by the University of Alabama at Birmingham's Institutional Review Boards for Human Use and qualified for exempt review. Single gestation infants who were born to US resident mothers from 1996 to 2000 with reported gestational age values of 25 to 42 weeks were included in this analysis. Gestational age in completed weeks was computed from the

Results

Table I depicts the ratio of the neonatal mortality rate at selected birth weight percentiles relative to the average neonatal mortality rate for the 45th to 55th percentiles for gestational ages of 25 to 42 weeks. The rate ratios varied across birth weight percentiles and gestation. For example at 26 weeks of gestation, infants at the 10th percentile of birth weight for gestational age experienced a 3-fold risk of dying within the first 28 days of life (relative to the “normal” comparison

Comment

An important limitation of the current method of defining SGA is the lack of a reference to the level of neonatal death risk that the 10th percentile of birth weight might entail at each gestational age. Although current SGA birth weight thresholds permit the identification of infants whose risk for an adverse outcome may be greater than appropriately grown infants, the relative increases in risk are not enumerated. In addition, the differential in risk between SGA and average-for-gestational

References (33)

  • R.W. Platt

    The effect of gestational age errors and their correction in interpreting population trends in fetal growth and gestational age-specific mortality

    Semin Perinatol

    (2002)
  • J.O. Gardosi

    Prematurity and fetal growth restriction

    Early Hum Dev

    (2005)
  • R.L. Deter

    Individualized growth assessment: evaluation of growth using each fetus as its own control

    Semin Perinatol

    (2004)
  • R.K. Creasy et al.

    Intrauterine growth restriction

  • Fetal growth restriction

  • R.M. Kliegman et al.

    Intrauterine growth retardation

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    Supported in part by Department of Health and Human Services, Health Resources and Services Administration, Maternal and Child Health Bureau grants: T03MC00007 and MCJ009040.

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