Correspondence

Children with Very Low Birth Weights

N Engl J Med 1995; 332:684-685March 9, 1995

Article

To the Editor:

Hack et al. (Sept. 22 issue)1 recently reported adverse outcomes in extremely-low-birth-weight children at school age, using a population-based sample from the presurfactant era. Their article and McCormick's editorial2 both express the critical need to prevent extreme prematurity. Although we concur with the general conclusions, we wish to point out that the sample studied is not necessarily representative of other regions of North America.

Population-based outcome data have been reported3,4 for preterm infants from the Canadian province of Alberta, where there are well-developed regional programs of perinatal and neonatal care that emphasize the antepartum identification of high-risk pregnancies, early maternal referral, organized transport, and active outreach education. Unpublished data on the 1986 birth cohort in Alberta are shown in Table 1Table 1Comparison of Population-Based Outcome Studies of Preterm Infants Weighing 500 to 749 g at Birth. for comparison with the Ohio data of Hack et al.1

The Alberta data show the potential for reducing the birth rate of infants with birth weights of 500 to 749 g (Ohio, 2.8 per 1000 live births; Alberta, 1.6 per 1000; chi-square, 19.1; P<0.001). The data also show that more of these fragile babies were born in tertiary care facilities in Alberta (Table 1). It is possible that in the case of some of the 44 percent of survivors in the study by Hack et al.1 who were small for their gestational age there were maternal or fetal complications that increased the likelihood of disability. Although the Alberta study does not contain data on school-age children for direct comparison, the percentage of children with major neurosensory disability at the age of three years was smaller. A breakdown of the Ohio data to show the outcomes at school age in subjects who were free of major neurosensory disability would be of interest. Some published information has suggested that preterm infants born weighing 500 to 749 g since the introduction of surfactant have fewer major neurosensory disabilities than comparable infants born earlier.4,5 We await reports on the outcomes of these children at school age with interest. The article by Hack et al.1 provides excellent information on which to base future comparisons.

Charlene M.T. Robertson, M.D.
Glenrose Rehabilitation Hospital, Edmonton, AB T5G 0B7, Canada

Reginald S. Sauve, M.D.
Alberta Children's Hospital, Calgary, AB T2N 1N4, Canada

Philip C. Etches, M.D.
Royal Alexandra Hospital, Edmonton, AB T5H 3V9, Canada

5 References

1. 1

   Hack M, Taylor HG, Klein N, Eiben R, Schatschneider C, Mercuri-Ninich N. School-age outcomes in children with birth weights under 750 g. N Engl J Med 1994;331:753-759
   Full Text | Web of Science | Medline

2. 2

   McCormick MC. Survival of very tiny babies -- good news and bad news. N Engl J Med 1994;331:802-803
   Full Text | Web of Science | Medline

3. 3

   Robertson CM, Hrynchyshyn GJ, Etches PC, Pain KS. Population-based study of incidence, complexity, and severity of neurologic disability among survivors 500 through 1250 grams at birth: a comparison of two birth cohorts. Pediatrics 1992;90:750-755
   Web of Science | Medline

4. 4

   Robertson C, Sauve RS, Christianson HE. Province-based study of neurologic disability among survivors weighing 500 through 1249 grams at birth. Pediatrics 1994;93:636-640
   Web of Science | Medline

5. 5

   Casiro O, Bingham E, MacMurray B, et al. Double-blind one-year follow-up of 89 infants with birth weights of 500-749 grams and respiratory distress syndrome randomized to two rescue doses of synthetic surfactant or air placebo: improved developmental outcome. J Pediatr (in press).
   

Author/Editor Response

The authors reply:

To the Editor: We welcome the opportunity to reemphasize the need to prevent prematurity in the United States. In 1992 the infant mortality rate in Canada was 6.1 per 1000 live births, 6th lowest in the world, whereas the United States ranked 22nd, with an infant mortality rate of 8.5.1 This difference reflects higher rates of prematurity in the United States associated with major sociodemographic and health care differences between the two countries. There are also differences within the United States and within the state of Ohio. For example, in the six-county region in Ohio that we studied from 1982 to 1986, the rates of live births of infants weighing 500 to 749 g ranged from 0.14 and 0.15 for Lake and Geauga counties to 0.29 and 0.47 for Cuyahoga and Lorain counties, respectively.

Some of the differences in the reported rates of live births in this weight group may, however, be due to differences in the classification of live birth as compared with stillbirth in infants born at the lower limit of viability.2,3

Our lower rate of infants born in tertiary care facilities (173 of 408, or 42 percent) may be due to a tendency toward deregionalization in Ohio in the 1980s. Robertson et al. also note our high rate of infants who are small for their gestational age. We must admit that these rates are a “best guess,” since there is concern about the reliability of estimates of gestational age and the growth charts we used did not extend below 25 weeks' gestation. We have no evidence that infants who are small for their gestational age have poorer developmental outcomes.

Differing definitions of the severity of neurologic impairment make comparison difficult.4 We question the representativeness of the low rate of major neurosensory disability in 1986 reported by Robertson et al. In the two publications they cite, neurologic-disability rates of 15 percent are reported for survivors with birth weights of 500 to 749 g born in the years 1988, 1989, and 1990. They also note a possible improvement in developmental outcomes in the surfactant era. However, despite a substantial increase in the survival of infants weighing 500 to 749 g at birth, our own unpublished data and the results of others5 have shown no differences in two-year neurodevelopmental outcomes after the use of surfactant.

A breakdown of our data on our subjects who were free of neurosensory disability is presented in Table 1Table 1Incidence of Findings Suggestive of Disabling Conditions in Neurologically Intact Children.. The substantially higher frequency of deficits in test performance persists even when disabled children are not included.

Maureen Hack, M.D.
H. Gerry Taylor, Ph.D.
Nancy Klein, Ph.D.
Case Western Reserve University, Cleveland, OH 44106

5 References

1. 1

   Wegman ME. Annual summary of vital statistics -- 1993. Pediatrics 1994;94:792-803
   Web of Science | Medline

2. 2

   Hack M, Fanaroff AA. Outcomes of extremely-low-birth-weight infants between 1982 and 1988. N Engl J Med 1989;321:1642-1647
   Full Text | Web of Science | Medline

3. 3

   Robertson C, Sauve RS, Christianson HE. Province-based study of neurologic disability among survivors weighing 500 through 1249 grams at birth. Pediatrics 1994;93:636-640
   Web of Science | Medline

4. 4

   McCormick MC. Has the prevalence of handicapped infants increased with improved survival of the very low birth weight infant? Clin Perinatol 1993;20:263-277
   Web of Science | Medline

5. 5

   Ferrara TB, Hoekstra RE, Couser RJ, et al. Survival and follow-up of infants born at 23 to 26 weeks of gestational age: effects of surfactant therapy. J Pediatr 1994;124:119-124
   CrossRef | Web of Science | Medline