Outcome of Infants Weighing Less Than 800 Grams at Birth: 15 Years' Experience

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Outcome

of

Infants

Weighing

Less

Than

800 Grams

at Birth:

15 Years’

Experience

Timothy R. La Pine, MD*;

J.

Craig Jackson, MDX; and Forrest C. Bennett, MD

ABSTRACT. Objective. Mortality and

neurodevelop-mental morbidity among infants weighing less than 800 g at birth are compared in three separate studies from the same intensive care nursery during an almost 15-year

period.

Methods. The survival and neurodevelopmental

out-come of 210 infants with birth weights less than 800 g

admitted to the University of Washington neonatal

in-tensive care unit between 1986 and 1990 are compared with those of two previous cohorts (1977 through 1980 and 1983 through 1985) of extremely low birth weight (ELBW) infants from the same nursery.

Results. Annual admissions of these ELBW infants

nearly doubled from 1977 to 1990, whereas nursery sur-vival rose from 20% between 1977 and 1980, to 36% between 1983 and 1985, to 49% in this current study of births between 1986 and 1990. The greatest increase in survival among the three studies occurred among infants with birth weights less than 700 g. Female survival was 20% higher than male survival in each of the time pen-ods. The prevalence of major neurosensory impairments did not differ significantly among the three study groups (19%, 21%, and 22% respectively); male survivors were more commonly affected across time periods. There were no diffeiences in mean cognitive test scores between the current 1986 through 1990 birth cohort (94) and the two previous cohorts (1977 through 1980, 98; 1983 through 1985, 89)

Conclusions. The experience of our center with these

ELBW infants over time seems reassuring to the extent that progressive increases in nursery survival have not resulted in increased neurodevelopmental morbidity.

Pediatrics 1995;96:479-483; extremely low birth weight,

prematurity, mortality, neurodevelopmental morbidity

and outcome, neonatal intensive care unit, high-risk

follow-up.

ABBREVIATIONS. ELBW, extremely low birth weight; NICU,

neonatal intensive care unit.

Advances in perinatal and neonatal treatment

ex-pertise and technology during the past several

de-cades have led to a dramatic increase in the survival of ever lower birth weight infants. Survival rates for

extremely low birth weight (ELBW; 1000 g or less)

infants have risen from 4% in the early 1950s to

From the *Depaent of Pediatrics, University of Utah Medical Center, Salt

Lake City; and the Department of Pediatrics, Child Development and Mental Retardation Center, University of Washington, Seattle.

Received for publication Aug 25, 1994; accepted Dec 2, 1994.

Reprint requests to (F.C.B.) Clinical Training Unit, CDMRC (WJ-10), Uni-versity of Washington, Seattle, WA 98195.

recent reports of 50% to 80% or more.”3 This

in-creased survival has stimulated considerable debate about the aggressiveness of treatment as the

poten-tial for acceptable outcome is weighed against the

risk of long-term disability, the wishes of parents, and the financial costs. Concern is expressed that the

increased survival accomplished in this population is

accompanied by increasing major

neurodevelop-mental morbidity in the forms of cerebral palsy,

mental retardation, and sensory impairments.’4’8

Conversely, others argue that aggressive intensive

care treatment of these infants is associated with both improved survival and better neurodevelopmental outcome.’9

The increasing likelihood of survival during the

past two decades of infants weighing less than 800 g

at birth has prompted critical examination of the

specific mortality and neurodevelopmental

morbid-ity of this subgroup of ELBW infants. In the most

recent follow-up studies of this population, nursery

mortality has varied between 40% and 70%, with the

prevalence of major neurosensory impairments in

survivors ranging between 15% and 40%.2427 Most of

this literature is composed of reports from single

centers at one observation point, thereby rendering it difficult to delineate temporal trends in the status of these most vulnerable infants clearly.

Previously, in two separate studies from two

dif-ferent time periods, Bennett et al3 examined the early

neurodevelopmental outcome of infants weighing

less than 800 g at birth who were cared for at the

University of Washington Medical Center. In these

studies, nursery mortality declined from 80%

be-tween 1977 and 1980 to 64% between 1983 and

1985,’#{176}with no significant difference in the

preva-lence of major neurosensory impairments (19% and

21 %, respectively). However, an increased severity of disability was noted in the 1983 through 1985 cohort,

suggesting that overall morbidity may have

wors-ened with increased survival. In this study, we com-pare a third birth cohort between 1986 and 1990 from

the same intensive care nursery at the University of

Washington with the two earlier cohorts to examine

the mortality and neurodevelopmental morbidity

trends of this unique population of extremely

pre-mature infants during an almost 15-year period.

Population

METHODS

Between January 1, 1986, and December 31, 1990, a total of 210 newborns weighing less than 800 g were admitted to the

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64% 52/81

51%

39/77

.

Ca

70

60

50

40

30

20

10

0

24% 10/42

700-799 600-699 500-599 400-499 Birthweight (gm)

purposes of this study, these newborns constitute the current

cohort. The two previously reported cohorts included 128 NICU

admissions between 1983 and 198510 and 95 NICU admissions

between 1977 and 1980. Vigorous neonatal resuscitation and

ag-gressive intensive care were consistently administered to those

newborns who displayed indications of viability throughout the

three study periods. No substantive changes in basic delivery

room resuscitation policies occurred during the three study

pen-ods. Data were collected for all liveborn infants and for outborn infants admitted during the first week of life. Treatment priorities in this nursery have been previously reported.28 Prophylactic

sun-factant use became common in 1988.29 The incidence of

broncho-pulmonary dysplasia is similar to that in six other major centers.#{176}

The incidence of retinopathy of prematurity is low compared with

other centers.3’ The rate of intracranial hemorrhage by the Papile classification system32 was 27% grade I, 19% grade II, 9% grade III,

and 6% grade IV.

The 210 infants admitted during the current study period had

a mean birth weight of 655 g (range, 420 through 799 g) and a

mean gestational age of 25 weeks (range, 22 through 31 weeks). Of

these 210 infants, 102 (49%) survived to discharge from the NICU

(Table 1). These surviving infants had a mean birth weight of 695

g (range, 457 through 795 g) and a mean gestational age of 25

weeks (range, 24 through 31 g). They consisted of 67 (66%) girls and 35 (34%) boys. There was no difference in either birth weight or gestational age by gender. Of the survivors, I I % were outborn,

and 42% had commercial insurance coverage; these percentages

have not changed substantially from 1977.

Methods

Infants discharged from the NICU received developmental

fol-low-up evaluations in the University of Washington High-Risk

Infant Follow-Up Clinic. This clinic has been in continuous oper-ation with the same medical director (F.C.B.) and the same assess-ment protocol since 1975. The follow-up clinic uses an

interdisci-plinary, neurodevelopmental team to monitor the growth, vision

and hearing, neurologic status, general cognition, and motor and

language function of our NICU graduates. Neuromotor function is

assessed by both a developmental pediatrician and a physical

therapist. Cognitive and linguistic development is measured by a

clinical psychologist. The standardized assessment instruments used in this study were: (1) the Bayley Scales of Infant Develop-ment (Mental and Motor scales);33 (2) the Stanford-Binet

Intelli-gence Scale (3rd edition);M and (3) the Wechsler Preschool and

Primary Scales of Intelligence-Revised.35 The specific test used was determined by the child’s age and abilities. Conceptional age (ie,

chronologic age corrected for prematurity) was used when

com-puting all developmental scores. Similar to the two previous

re-ports from our center, developmental scores from the three

instru-ments were combined to obtain a mean cognitive score for group

analysis and comparison purposes. Outcome information from the

most recent individual assessment was used in this study; the

median study age was 19 months corrected age with a range of 4

to 54 months.

A major neurosensory impairment was considered present if:

(1) the mental development or intelligence test score was more

than 1 .5 SD below the test mean (ie, less than 80); (2) cerebral palsy

was diagnosed, or the motor development score was more than I .5

SD below the test mean (ie, less than 80) in conjunction with

neuromotor abnormalities; or (3) a permanent visual or hearing

impairment was diagnosed. In the state of Washington, a child

whose mental or motor development score is less than 80 qualifies for state-supported developmental intervention services.

Group and subgroup means were compared using the

two-tailed Student’s t test. Outcomes among subgroups were

compared by x analysis.

TABLE 1. Infants Weighing

Admitted, Discharged, and Follo

Less Than 800 g at Birth

wed Between 1986 and 1990

1986-1990 N Boys/ Birth Weight, Gestational

Cohort Girls g (Mean-Range) Age, wk

(Mean-Range)

NICU Admissions 210 91/119 655 (420-799) 25 (22-31)

Survivors 102 35/67 695 (457-795) 25 (24-31)

Follow-up 78 31 /47 696 (457-795) 25 (24-31)

Survival

RESULTS

Nursery survival in the current cohort was 49%

(102 of 210). The two previous cohorts at our center

demonstrated 20% (19 of 95) survival between 1977

and 1980 and 36% (46 of 128) survival between 1983

and 1985. This represents an increase in survivorship

over time of approximately 15% between each of the

study groups

(P

< .01).

The Figure illustrates birth weight subgroup

sun-vival for the current cohort and for the 1983 through

1985 cohort. Infants with birth weights between 700

and 799 g had 64% (52 of 81) survival in the current

cohort compared with 53% (29 of 55) between 1983

and 1985. Infants with birth weights between 600 and

699 g had 51 % (39 of 77) survival in the current

cohort compared with 29% between 1983 and 1985

(13 of 45). Infants with birth weights between 500

and 599 g had 24% (10 of 42) survival in the current cohort compared with 16% (4 of 25) survival between 1983 and 1985. One of 10 infants (10%) in the current cohort with a birth weight less than 500 g survived;

there were no survivors in this subgroup between

1983 and 1985. Combining the subgroups with

weights less than 700 g, 39% (50 of 129) of admitted infants survived in the current cohort compared with

23% (17 of 73) between 1983 and 1985. Thus, the

greatest increase in the likelihood of survival

be-tween these two time periods occurred among

in-fants with birth weights less than 700 g, for whom

the rate of survival nearly doubled. In the 1977

though 1980 cohort, only 3 of the 19 surviving infants

had birth weights less than 700 g; 16 weighed

between 700 and 799 g.

In all three cohorts, female survival exceeded male

survival. In the current cohort, 56% (67 of I 19) of

female newborns survived to discharge compared

with 34% (35 of 91) of male newborns

(P

< .01).

Neurodevelopmental Morbidity

Of the 102 discharged infants in the current cohort,

78 (77%) were followed and directly evaluated. As

a

1983-1985 U 1986199J

Figure. Survival by birth weight subgroup of infants weighing

less than 800 g in the current (1986 through 1990) and 1983

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shown in Table 1, these evaluated infants are

repre-sentative of all ELBW infants discharged from our

NICU during the study period in terms of birth

weight and gestational age. The principal reasons for

not being followed included relocation out of the

region, distance to our facility, parental work

com-mitments, and frequent moves in foster care.

Major Neurosensory Impairments

Of the 78 infants followed in the current cohort, I

7

(22%) demonstrated at least one major neurosensory

impairment. As can be seen in Table 2, this

preva-lence of major impairment is not significantly differ-ent from that observed in the original 1977 through

1980 cohort (3 of 16, 19%) or the 1983 through 1985

cohort (8 of 38, 21 %). Distribution of major

impair-ment by birth weight subgroup was: 700 through 799

g, 8 of 39 (21 %); 600 through 699 g, 7 of 29 (24%); 500

through 599 g, 1 of 9 (11%); and 400 through 499 g, 1

of 1 (100%). Combining the subgroups with weights

less than 700 g, 23% (9 of 39) had major impairments, not statistically different from the 21 % (8 of 39) of infants weighing 700 g or more at birth.

Of the 17 disabled infants in the current cohort, II

(65%) had multiple impairments with combinations

of developmental retardation, cerebral palsy or

mo-ton delay, and visual or hearing impairments. This is

also consistent with the 1983 through 1985 cohort, in which six of the eight (75%) disabled infants

demon-strated multiple impairments. In the 1977 through

1980 cohort, none of the three disabled infants were

multiply impaired. In the current cohort, visual

im-pairment (ie, permanent sequelae of retinopathy of prematurity) remained in eight infants studied, four

of whom were assessed to be in the acuity range of

legal blindness. In contrast, only one infant studied

sustained a sensonineural hearing impairment.

In the current cohort, 10 of 31 (32%) followed boys

exhibited at least one major neurosensory

impair-ment compared with 7 of 47 (15%) followed girls

(P

= .06). This gender difference is consistent with

that in the 1983 through 1985 cohort (3 of 10, 30%

boys; 5 of 28, 18% girls).

Cognitive Test Scores

The mean cognitive score of the current cohort was

94 (range, 50 through 124), which is not significantly

different from the two previous cohorts (1977

through 1980, 98 with a range of 50 through 127; 1983

through 1985, 89 with a range of 52 through 122).

There were no significant differences in cognitive or

motor test scores between individual birth weight

subgroups with the exception of the one infant

weighing less than 500 g with lower scores (Table 3).

TABLE 2. Pre

and Mean Cogniti

valence of Major ye Test Scores in t

Neurosensory Impairments he Three Study Cohorts Major

Neurosensory

Impairment

Mean Cognitive Test Score

1986-1990

1983-1985

1977-1980

17/78 (22%)

8/38 (21%)

3/16 (19%)

94 (50-124) 89 (52-122) 98 (50-127)

In the original 1977 through 1980 cohort, a gender difference existed in mean cognitive test scores (girls, 105; boys, 89). This gender difference was not appar-ent in the 1983 through 1985 cohort (girls, 89; boys, 88) or in the current cohort (girls, 96; boys, 93).

DISCUSSION

At the University of Washington, intensive care

nursery admissions of newborns weighing less than

800 g increased from 95 (24 per year) in the original

study period between 1977 and 1980 to 210 (42 per

year) in the current study period between 1986 and

1990. This is consistent with admission trends

re-ported elsewhere during this almost 15-year period5’7

and most likely reflects a more aggressive medical

approach and attitude toward ELBW infants. The

observed increase in nursery admissions has been

supported by a number of factors, including the

re-gionalization of peninatal care, which encourages early transport of high-risk maternity patients to ter-tiary medical centers, the increasing ability of

neona-tal care centers to achieve improved survival, and a

more optimistic long-term neurodevelopmental

out-come for these infants.

Coincident with the increased number of

admis-sions has been a steady increase in survival during

the three study periods. Survival increased from 20%

in the original cohort to 36% in the second cohort to

49% in the current cohort. Furthermore, preliminary

data from our intensive care nursery indicate that

this significant trend is ongoing, with a survival rate

for these ELBW infants exceeding 70% in the 2 years

after the completion of this study, primarily

associ-ated with the routine administration of exogenous

surfactant (our unpublished data). Survival remains linked to birth weight, with the highest survival per-centage (65%) occurring in infants with birth weights

between 700 and 799 g and progressively less for the

lower birth weight subgroups. Nevertheless,

al-though survival steadily increased during the three

study periods in all birth weight subgroups, the

greatest increase over time occurred at weights less

than 700 g, with a near doubling of survival.

Gender differences in survival continue to favor

girls by approximately 20% in each of the three study periods. This is in agreement with other centers that

report both improved survival and decreased

neuro-developmental morbidity for ELBW girls compared

with boys.37’

The neurodevelopmental outcome of the current

cohort in terms of major neurosensory impairments and cognitive test scores was similar to that reported

for both of the previous cohorts from our medical

center. Specifically, we found no evidence of an

in-TABLE 3. Mean

Weight Subgroup

Cognitive and Motor Test Scores by Birth

Birth Weight Cognitive (Mental)

Score

Motor

Score

700-799 (n = 39) 90 (54-134) 90 (50-135)

600-699 (n = 29) 97 (72-120) 88 (50-117)

500-599 (n = 9) 100 (52-131) 97 (72-124)

400-499(n=1) 74 80

at Viet Nam:AAP Sponsored on September 1, 2020 www.aappublications.org/news

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creasing rate of neurodevelopmental morbidity

dur-ing the almost 15-year period when the survival of

infants weighing less than 800 g was steadily and

significantly increasing. Consistent with the 1983

through 1985 cohort, major impairments occurred

predominantly among boys in the current cohort as

well. The severity of overall impairment, as

mea-sured by multiple major disabilities in the same

child, was greater in the second cohort than in the

original cohort, and this difference has persisted in

the current cohort. These multiply impaired children

demonstrated combinations of severe physical,

men-tal, and sensory disabilities, which likely will persist indefinitely.

The current results indicate that decreasing birth weight is a much better predictor of mortality than of

neurodevelopmental morbidity. The occurrence of

major impairments did not differ by birth weight

subgroup; surviving infants with birth weights less

than 700 g did not experience increased disability.

The likelihood of cognitive development being

within the average range and the obtained mean

cognitive test scores was not significantly different between birth weight subgroups in either the current

cohort or the 1983 through 1985 cohort. Although the

mean cognitive performance of the 1983 through

1985 cohort (89) was significantly

(P

= .05) lower

than that of the original cohort (98), there was no

significant difference between the current cohort (94) and the two previous groups. It should be noted that these early mean cognitive scores for all three ELBW

cohorts are within the accepted range of normal

development.

Results from this study and our collective experi-ence over time require cautious, critical

interpreta-tion. Several caveats must be considered. The

rela-tively short median duration of follow-up (19

months) precludes adequate description of the full

form and severity of major neurosensory

impair-ments. Furthermore, there is no way at this early age

to predict accurately the future occurrence and

im-pact of so-called minor central nervous system

im-pairments, ie, morbidities of coordination, language,

social competence, learning, and attention, which

manifest at older ages and which are reported to be

increasingly prevalent as birth weight and

gesta-tional age decline.39 The overall study design of

grouping subjects into distinct time periods for com-parison purposes required testing children at

differ-ent ages with different cognitive measures and

com-bining these scores in our analyses. The 24 surviving infants (23% of the eligible sample) lost to follow-up

may be at disproportionately higher risk of

neuro-developmental morbidity.’#{176}’4’

Nevertheless, despite these limitations, this study has important policy implications. With the changing role of medicine in society and the debate over health care reform, the survival and neurodevelopmental

outcome of ELBW infants has emerged as an issue of

great contemporary interest. Cost and family impact

concerns are increasingly discussed when

consider-ing the limits of neonatal viability.’43 The almost

15-year observation and reporting period from a

sin-gle tertiary neonatal care center is unique among

investigations in the United States. The longitudinal

experience of the senior investigator (F.C.B.)

pro-vides continuity of design and analysis for the three study periods. It is clear that greatly increased

num-bers of newborns weighing less than 800 g are being

admitted to intensive care nurseries. At the

Univer-sity of Washington NICU, these admissions nearly

doubled on an annual basis between 1977 and 1990.

It is also clear that the likelthood of long-term

sur-vival continues to move steadily and predictably

upward, particularly in the lowest birth weight sub-groups. In our experience, the overall survival rate

increased by approximately 30% between 1977 and

1990. The greatest improvement in survival occurred

for newborns weighing less than 700 g.

What is the neurodevelopmental impact of this

incredible technological ability to salvage life at and around 500 g birth weight and 24 weeks’ gestational age? In brief, it is better than anticipated by most

investigators and practitioners. As our study

docu-ments, the dramatic increases in survival have not

been accompanied by the corresponding increases in

the major neurodevelopmental morbidity of

survi-vors predicted by many critics. This is particularly

noteworthy in view of the increasing proportion of

ELBW survivors with birth weights less than 700 g.

Although the prevalence of major neunosensory

im-pairments in any community or geographic area

with access to neonatal intensive care services neces-sarily will increase because of increased survival, the

relatively stable rate of developmental disability

throughout the almost 15-year study period in

in-fants weighing less than 800 g at birth allows us to

conclude that early neurodevelopmental outcome is

acceptable for these tiny, fragile new survivors. To

what degree long-term developmental monitoring

into the early school years and beyond will temper

this posture of cautious optimism remains to be

de-termined. In the meantime, because the ultimate goal

of preventing extreme prematurity remains elusive,

these positive aspects of outcome must be part of the

current discussions concerning prioritization of

health services, limits of care, and expenditure of

public and private resources.

ACKNOWLEDGMENT

Supported in part by grant MCJ-539159 from the Maternal and

Child Health Bureau, Public Health Service, Department of Health and Human Services.

REFERENCES

I. Dweck HS. The tiny baby: past, present, and future. Clin Perinatol. 1977;4:425-431

2. Knobloch H, Malone A, Ellison PH, Stevens F, Zdeb M. Considerations in evaluating changes in outcome for infants weighing less than 1501

grams. Pediatrics. 1982;69:285-295

3. Bennett FC, Robinson NM, Sells CJ. Growth and development of infants

weighing less than 800 grams at birth. Pediatrics. 1983;71:319-323 4. Gerdes JS, Abbasi 5, Bhutain VK, Bowen FW Jr. Improved survival and

short-term outcome of inborn “micropremies.” Clin Pediatr. 1986;25: 391-394

5. Hack M, Fanaroff AA. Special report: changes in the delivery room care of the extremely small infant (<750 g): effects on morbidity and

out-come. N Engl JMed. 1986;314:660-664

(5)

survey 1f preterm and very low birth weight infants in the Netherlands.

Pediatrics. 1988;81:404-41 1

7. Hack M, Fanaroff AA. Outcomes of extremely-low-birth-weight infants between 1982-1988. N Engl JMed. 1989;321:1641-1647

8. Saigal S, Rosenbaum P, Stoskopf B, Sinclair JC. Outcome in infants

501-1000 gm birth weight delivered to the residents of the McMasters Health Region. JPediatr. 1989;105:969-976

9. Lubchenco LO, Butterfield J, Delaney-Black V, Goldson E, Koops BL,

LaZotte DC. Outcome of very-low-birth-weight infants: does

antepar-tum versus neonatal referral have a better impact on mortality,

mor-bidity or long term outcome? Am JObstet Gynecol. 1989;1960:539-454 10. Hoffman EL, Bennett FC. Birth weight less than 800 grams: changing

outcomes and influences of gender and gestation number. Pediatrics. 1990;8627-34

I I. Young EWD, Stevenson DK. Limiting treatment for extremely prema-ture, lo*v-birth-weight infants (500 to 750 g). Am

I

Dis Child. 1990;144:

549-552

12. Robertson CMT, Hrynchshyn GJ, Etches PC, Pain KS. Population-based

study of the incidence, complexity, and severity of neurologic outcome

among survivors weighing 500 through 1250 grams at birth: a compar-ison of two birth cohorts. Pediatrics. 1992;90:750-755

13. Allen MC, Donohue PK, Dusman AE. The limit of viability-neonatal

outcome of infants born at 22 to 25 weeks gestation. N Engl JMed.

1993;329:1597-1650

14. Schechner S. For the 1980s: how small is too small? Clin Perinatol.

1980;7:135-143

15. Dnllien CM. Growth and development in a group of children of very

low birth weight. Arch Dis Child. 1985;33:10-18

16. Collin MF, Halsey CL, Anderson CL. Emerging developmental sequelae in the “normal” extremely low birthweight infant. Pediatrics. 1991;88: 115-120

17. Ross G, Lipper EG, Auld PAM. Educational status and school-related abilities of very low birth weight premature children. Pediatrics. 1991;

88:1125-1134

18. McCormick MC. Has the prevalence of handicapped infants increased with improved survival of the very low birth weight infant? Clin Pen-natol. 1993;20:263-277

19. Stewart AL, Reynolds EOR. Improved prognosis for infants of very low

birth weight. Pediatrics. 197454:724-734

20. Driscoll JM, Driscoll YT, Steir ME. Mortality and morbidity in infants less than 1001 grams birth weight. Pediatrics. 1982;69:21-26

21. Horwood JP, Boyle MH, Torrance GW. Mortality and morbidity of

500-1499 gram birth weight infants livebom to residents of a defined geographical region before and after neonatal intensive care. Pediatrics.

1982;69:613-620

22. McCormick MC, Shapiro S. Starfield BH. The regionalization of

perina-tal services, summary of the evaluation of a national demonstration program. JAMA. 1985;253:799-804

23. Victoriai Infant Collaborative Group. Eight-year outcome in infants

with birth weight of 500 to 999 grams. Continuing regional study of

1979 and 1980 births. IPediatr. 1991;118:761-767

24. Sehring 5, Piecuch R. Medical and neurodevelopmental outcome of

extremely low birth weight (ELBW) infants. Clin Res. 1993;41:5A.

Abstract

25. Hack M, Taylor G, Klein N, Eiben R. Outcome of 750 gram birth weight infants at school age. A regional study. Pediatr Res. 1993;33:262A.

Abstract

26. Pearlman 5, Bristow K. Outcome of neonates < 800 grams cared for in a level 3 nursery-limits of viability. Pediatr Res. 199333:270A. Abstract 27. Pomerance II, Feldman M, Pomerance U, Harvin HJ, Kanaly KA.

Sur-vival of infants weighing 500-749 grams at birth in 50 gram increments. Pediatr Res. 1993;33:471A. Abstract

28. Overstreet DW, Jackson JC, van Belle G, Troug WE. Estimation of mortality risk in chronically ventilated infants with bronchopulmonary dysplasia. Pediatrics. 1991;88:1 153-1160

29. Hoekstra RE, Jackson JC, Myers TF, et al. Improved neonatal survival following multiple doses of bovine surfactant in very premature infants at risk for respiratory distress syndrome. Pediatrics. 1991;88:10-18 30. Avery ME, Tooley WH, Keller JB, et al. Is chronic lung disease in low

birth weight infants preventable? A survey of eight centers. Pediatrics.

1987;79:26-30

31. Valentine PH, Jackson JC, Kalina RE, Woodrum DE. Increased survival

of low birth weight infants: impact on the incidence of retinopathy of

prematurity. Pediatrics. 1989;84:442-445

32. Papile LA, Burstein J, Burstein R, Koffler H. Incidence and evolution of subependymal and intraventricular hemorrhage: a study of infants with

birthweights less than 1500 gm. IPediatr. 1978;92:529-534

33. Bayley N. Bayley Scales of Infant Development. New York: Psycological

Corp; 1969

34. Terman LM, Merrill MA. The Stanford-Binet Intelligence Scale. 3rd ed rev. Boston: Houton Mifflin; 1973

35. Wechsler D. Manual for the Wechsler Intelligence Scale for Children-Revised.

New York: Psychological Corp; 1974

36. Lee 5K, Penner PL, Cox M. Comparison of the attitudes of health care professionals and patients toward active treatment of very low birth weight infants. Pediatrcs. 1991;88:1 10-114

37. Hirata T, Epcar JT, Walsh A, et al. Survival and outcome of infants 501

to 750 gm: a six-year experience. IPediatr. 1983;102:741-748

38. Brothwood M, Wolke D, Gamsu H. Prognosis of the very low birth

weight baby in relation to gender. Arch Dis Child. 1986;61:559-564 39. Bennett FC. Developmental outcome. In: Avery GB, Flecther MA,

Mac-Donald MG, eds. Neonatology: Pathology and Management of the Newborn.

4th ed. Philadelphia: Lippincott; 1994:1367-1386

40. Lasky RE, Tyson JE, Rosenfeld CR, et al. Disappointing follow-up

findings for indigent high-risk newborns. Am I Dis Child. 1987;147: 100-105

41. Faison CF, Dodge E, Bennett FC. Outcome of low birthweight

prema-ture infants not regularly followed in a high risk neonatal follow-up

clinic. Clin Res. 1994;42:69A. Abstract

42. Pomerance JJ, Pomerance U, Gottlieb JA. Cost of caring for infants weighing 500-749 g at birth in 50 gram increments. Pediatr Res. 1993; 33:231A. Abstract

43. Cronin CM, Shapiro CR, Castro 0, Cheang M. Impact of very low birth weight infants (VLBW) on the family: a case-control study. Pediatr Res.

1993;33:259A. Abstract

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1995;96;479

Pediatrics

Timothy R. La Pine, J. Craig Jackson and Forrest C. Bennett