The Journal of Pediatrics
Volume 145, Issue 2 , Pages 278-279, August 2004

Outcomes of SGA infants

Perinatal Infectious Disease Epidemiology Unit, Department of Obstetrics, Prenatal Medicine, and General Gynecology and Department of Pediatric Pneumology and Neonataology, Hanover Medical School, Hanover 30623 Germany

Article Outline

 

To the Editor:

The recent study by Regev et al1 is based on a cohort of very-low-birth-weight (VLBW, <1500 g) infants and focuses on the outcome of those who were small-for-gestational-age (SGA). The authors acknowledge that analyses in birth weight-defined cohorts might be biased by different proportions of SGA infants in each week of gestational age (GA).2., 3. The GA cutoff they chose results in exactly this, eg, 12% SGA at 24 to 25 weeks, and 18% at 30 to 31 weeks. The growth standards used were not sex-specific. Moreover, they are also outdated. Because the average birth weight increases over time,4 newborns might be misclassified as non-SGA who should have been classified as SGA. For example, a male newborn with a GA of 30 weeks and a birth weight of 1050 g would have been classified as non-SGA according to the cutoff6 used by Regev et al, but being SGA according to the more current definition as a birthweight below the 10th percentile5 using more recent standards7 (Table). The comparison group in the study by Regev et al seems to include appropriate-for-gestational-age (AGA) as well as large-for-gestational-age (LGA) infants. AGA and LGA infants risk profiles might differ substantially.8 I suggest that these two subgroups may not be a single homogenous comparison group.

Table. Definition of SGA according to Usher et al6 as a birth weight 2 SD below the mean, and according to Voigt et al7 as a birth weight <10th percentile
Usher et al (1959-63) n=300Voigt (1992) n=563,480
Birth weight/GA (wk) Male singletonFemale singleton
Mean−2 SDMedian10th percentileMedian10th percentile
25850650800590760560
3013731023152010701420990
35234717172640206025501980

Numbers are given for 25, 30, and 35 weeks' gestation for illustration purpose. All data are given in grams.

The major fallacy is the rather general conclusion in the abstract “that major morbidity among [SGA] survivors was increased.” First, no significant risk increase was noted for half of the severe morbidities observed (severe intraventricular hemorrhage, periventricular leukomalacia, and necrotizing enterocolitis). Second, the differences found for the other half (severe retinopathy of prematurity, respiratory distress syndrome, and bronchopulmonary dysplasia) might be due to lack of adjustment for relevant postnatal confounders such as duration/intensity of oxygen supplementation and ventilation.9., 10. Adjustment only for antenatal events makes risk analyses of late neonatal outcomes prone to distortion by uncontrolled influence of postnatal events.

Future use of well-defined study populations, up-to-date growth standards, appropriate adjustment for confounders, and avoidance of potentially misleading conclusions will result in a reduction of inconsistencies in the SGA literature.

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References 

  1. Regev RH, Lusky A, Dolfin T, Litmanovitz I, Arnon S, Reichman B. Excess mortality and morbidity among small-for-gestational-age premature infants: a population-based study. J Pediatr. 2003;143:186–191
  2. Arnold CC, Kramer MS, Hobbs CA, McLean FH, Usher RH. Very low birth weight: a problematic cohort for epidemiologic studies of very small or immature neonates. Am J Epidemiol. 1991;134:604–613
  3. Dammann O, Dammann CE, Alfred EN, Veelken N. Fetal growth restriction is not associated with a reduced risk for bilateral spastic cerebral palsy in very-low-birthweight infants. Early Hum Dev. 2001;64:79–89
  4. Kramer MS, Morin I, Yang H, Platt RW, Usher R, McNamara H, et al.  Why are babies getting bigger? Temporal trends in fetal growth and its determinants. J Pediatr. 2002;141:538–542
  5. Kramer MS. Determinants of low birth weight: methodological assessment and meta-analysis. Bull World Health Org. 1987;65:663–737
  6. Usher R, McLean F. Intrauterine growth of live-born Caucasian infants at sea level: standards obtained from measurements in 7 dimensions of infants born between 25 and 44 weeks of gestation. J Pediatr. 1969;74:901–910
  7. Voigt M, Schneider KT, Jahrig K. [Analysis of a 1992 birth sample in Germany. 1: New percentile values of the body weight of newborn infants]. Geburtshilfe Frauenheilkd. 1996;56:550–558
  8. Heinonen KM, Jokela V. Multiple fetuses, growth deviations and mortality in a very preterm birth cohort. J Perinat Med. 1994;22:5–11
  9. Seiberth V, Linderkamp O. Risk factors in retinopathy of prematurity. A multivariate statistical analysis. Ophtalmologica. 2000;214:131–135
  10. Clark RH, Germann DR, Jobe AH, Moffitt ST, Slutsky AS, Yoder BA. Lung injury in neonates: causes, strategies for prevention, and long-term consequences. J Pediatr. 2001;139:478–486

PII: S0022-3476(04)00240-9

doi:10.1016/j.jpeds.2004.03.040

Refers to article:

  • Excess mortality and morbidity among small-for-gestational-age premature infants: a population-based study

    Rivka H. Regev, Ayala Lusky, Tzipora Dolfin, Ita Litmanovitz, Shmuel Arnon, Brian Reichman, in collaboration with the Israel Neonatal Network
    The Journal of Pediatrics August 2003 (Vol. 143, Issue 2, Pages 186-191)

The Journal of Pediatrics
Volume 145, Issue 2 , Pages 278-279, August 2004

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