Very Low Birth Weight and Growth to Age 8 YearsI: Weight and Height

William H. Kitchen, MD, FRACP; Lex W. Doyle, MD, MSc, FRACP;Geoffrey W. Ford, MB,BS, FRACP; Catherine Callanan, RN

\s=b\We determined the heights and weights at ages 2, 5, and8 years for the following three cohorts of children: group 1with birth weights between 500 and 999 g; group 2 withbirth weights between 1000 and 1499 g; and group 3 withbirth weights more than 2500 g. By age 8 years, group 3children were significantly heavier and taller than all chil-dren in groups 1 and 2 combined; group 1 children weresignificantly shorter than those in group 2, but their weightswere similar. From ages 2 to 5 years, annual increments inweight and height were similar in all three groups; however,between ages 5 and 8 years, children in group 3 grew fasterthan those in groups 1 and 2 combined, and children ingroup 1 had smaller height increments than those in group2. Of children with birth weights less than 1500 g, with aweight or height under the 10th percentile at age 2 years,only approximately one half were still below the 10th per-centile for the corresponding measurement at age 8 years.Health variables determined before birth, such as maternalheight or birth weight ratio, were more important thanhealth after birth in predicting a height or weight below the10th percentile at age 8 years in children with birth weightsless than 1500 g.(AJDC. 1992;146:40-45)

Reports from several countries indicate that childrenwith very low birth weight (VLBW, birth weight lessthan 1500 g) often grow poorly in early childhood.1"8 Thisproblem is even more prevalent in children with extremely low birth weight (ELBW, birth weight less than1000 g).68"12 Until synthetic growth hormone became

See also

46.

widely available, short stature in these children was usually a matter of academic rather than practical interest.Children with VLBWs, especially ELBWs, of short stature

are an obvious group for a trial of synthetic growth hormone; however, data are limited on their height after earlychildhood, particularly for ELBW children born in the eraof modern neonatal intensive care. Their adult stature isuncertain.

In an earlier report, we were unable to find convincingevidence of catch-up growth between ages 2 and 5 yearsin a cohort of 135 children withbirth weight under 1501 g.12However, only 28 children had ELBW, and the time spanof 3 years was relatively short. We therefore reassessed thegrowth of all available children in our longitudinal studieswho had reached age 8 years, including a group of childrenwith normal birth weight (birth weight more than 2500 g).We identified the following three groups of children:group 1 consisted of children with birth weight between500 and 999 g; group 2 consisted of children with birthweight between 1000 and 1499 g; and group 3 consisted ofchildren with birth weight more than 2500 g.

The aims of the study were: (1) to contrast the heightand weight achieved by age 8 years between the threebirth-weight groups; (2) to contrast the growth rates between ages 2, 5, and 8 years between the three groups; (3)to seek evidence of catch-up growth of those VLBW children who were underweight or of small stature at age 2years; and (4) to determine whether prenatal or postnatalvariables were more important in predicting height orweight below the 10th percentile at age 8 years in VLBWchildren.

PATIENTS AND METHODSThe children in this report comprised two cohorts of preterm

infants and a normal-birth-weight comparison group. Group 1comprised 79 consecutive children with birth weight between500 and 999 g born between January 1,1977, and March 31,1982.Group 2 included 111 consecutive children with birth weight between 1000 and 1499 g born between October 1,1980, and March31,1982. Group 3 comprised 56 randomly selected children withbirth weight over 2500 g born during the same period as thegroup 2 children.

In the original cohorts from which these children werederived, there were 85 children with birth weights less than1000 g, 124 with birth weights between 1000 and 1500 g, and 60with birth weights more than 2500 g. For the present study, threegroups of children were excluded from the original cohorts: eightnonwhite children; 11 children with moderate or severe physical disability from cerebral palsy; and to conform with the con-

Accepted for publication July 22, 1991.From the Departments of Obstetrics and Gynecology (Drs

Kitchen and Doyle) and Pediatrics (Dr Kitchen), University of Mel-bourne, Australia, and the Royal Women's Hospital, Melbourne (DrFord and Ms Callanan).

Reprints not available.

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vention of 1499 g as the upper limit of VLBW, four children withbirth weight exactly 1500 g.

All children were born in the Royal Women's Hospital, Melbourne, Australia, a tertiary center with approximately 6000births annually from 1977 to 1982; many mothers were at lowrisk, but the hospital was also a referral center for patients withcomplications of pregnancy who had been booked elsewhere fordelivery. The population included families from a wide socio-economic spectrum, with social class being based on the occupation of the principal income earner. Mothers were designatedas immigrants if they were from a country in which English wasnot the first language. The duration of the mother's schoolingwas divided into less than 10 years or 10 years or more. Somefamilies paid fees.

All available children in groups 1, 2, and 3 were assessed onthree occasions, as close as possible to ages 2, 5, and 8 years,corrected for prematurity. Weight and standing height weremeasured in a standardized fashion1314; data on a few childrenliving out of the state of Victoria were obtained from other professional sources. The number and duration of hospital read-missions and illnesses were confirmed with the relevant hospital or medical practitioner. Hospital readmissions were classifiedaccording to whether the primary diagnosis was medical or surgical. The percentiles for weight and height originally had beencoded using Australian reference data obtained in the early 1970son a multiracial urban community.1516

The percentiles were then recoded using the National Center for Health Statistics reference values17 now recommendedby the World Health Organization for international comparison.18 The reference values for the 5th, 10th, 25th, 50th, 75th,90th, and 95th percentiles were entered into a computer, andthe weight and height of each child was computed into oneof the eight possible percentile channels (lower than the 5th,5th to 10th, etc). Continuous variables for weight and heightsuitable for multivariate analyses were computed; ratios ofweight and height for age were calculated by dividing theobserved growth measurement of each child by the 50th percentile reference value listed by the National Center forHealth Statistics. These ratios are frequently used in nutritional studies.19 Similarly, for each child, the ratio of observedbirth weight to the 50th percentile for the child's gestationalage obtained from reference data applicable to our hospitalpopulation in the 1970s20 was computed.21 The ratio of lengthat birth to the 50th percentile was not computed, since lengthat birth was not measured for all infants. For children withdata available at each age, average annual increments inweight and height were computed during the 3-year intervalsbetween 2 and 5 years and 5 and 8 years. Because the intervals between assessments were often not exactly 3 years, theaverage annual growth increments were calculated by dividing the increase in height or weight between assessments bythe exact interval between the measurements.

The height and weight ratios achieved by age 8 years and theannual growth increments between ages 2 and 5 years and ages5 and 8 years were compared between the three groups usinganalysis of variance, adjusting for gender when appropriate. Foreach analysis of variance, linear contrasts were used, first tocompare the normal-birth-weight children (group 3) with allVLBW children (groups 1 and 2), and if this difference was significant, to compare ELBW children (group 1) with larger VLBWchildren (group 2).Of particular interest to the clinician is the outcome of theshortest and lightest children, particularly those below the 10thpercentile. Children with birth weight less than 1500 g at age 2years were divided into four groups: below the 5th percentile,between the 5th and 10th percentiles, between the 10th and 25thpercentiles, and 25th percentile and above; and their values werecompared with those at ages 5 and 8 years.

To determine the variables that might predict whether a VLBWchild would be below the 10th percentile for weight or height atage 8 years, the data were analyzed with logistic regression. Theindependent variables studied in chronologic order were socio-

demographic factors (social class, mother's duration of schooling, immigrant status, and maternal height), perinatal factors(gestational age, birth-weight ratio, gender, multiple pregnancy,antenatal steroids, parenteral alimentation, duration of ventilation, and bronchopulmonary dysplasia), health from dischargeto age 8 years (asthma or recurrent lower respiratory tract infections at age 8 years, and the requirement for hospital readmissions for predominantly medical or surgical indications fromdischarge to age 2 years, from age 2 to 5 years, and from age 5to 8 years).

Data were analyzed with a computer using Statistical Packagefor the Social Sciences-X (SPSS-X) programs.22 In addition to thestatistical tests already mentioned, comparison of categoricalvariables was done with

2 analysis or Fisher's Exact Test, andcontinuous variables, with Mann-Whitney U test. A value ofP

Table 1.Biographical Data on Children Survivingto Age 8 Years

Group1

(n = 79)2

(n = 111)3

(n = 56)Birth weight range, gMedian (10th-90th

percentiles)Birth weight, gGestational age,

wkAge at presen

tation, moSociodemographic

data, No. (%)of patients

Social classProfessional/

managerialSkilled/semiskilledUnskilled/social

securityNo data

Maternaleducation, y

Table 2.Average Annual Incremental Weight andHeight Gains for Extremely Low-Birth-Weight, LargerVery-Low-Birth-Weight, and Normal-Birtn-WeightCohorts (No Data Missing From Any Age Group)

Group1 2 3

(n = 72) (n = 93) (n = 37)Birth weight 500-999 1000-1499 >2500

range, gAverage annual increment,

median (10th-90th percentiles)Weight, kg/y

2 to 5 y 1.80(1.35-2.73) 1.96(1.33-2.95) 2.11(1.63-3.35)5 to 8 y 2.14(1.53-3.64) 2.34(1.71-3.94) 3.05(1.90-5.08)*

Height, cm/y2 to 5 y 7.46(6.26-8.61) 7.46(6.56-8.65) 7.59(6.54-8.92)5 to 8 y 5.65(4.64-6.86) 6.10(5.31-7.19)+ 6.37(5.33-7.21)*

*For group 3 compared with groups 1 and 2 combined, P

normal-birth-weight group (group 3). The only immigrants excluded from our study were Asians, for reasonsgiven previously. Both immigrant mothers and multiplepregnancies were not large influences on growth in ourstudy, and neither was significantly associated withgrowth failure at age 8 years. Consequently, we did notexclude children from multiple pregnancies or born toimmigrant mothers.

In our study, VLBW children were significantly shorterand lighter at age 8 years than the normal-birth-weightchildren, observations consistent with our previous report on a smaller cohort of VLBW children at ages 2 and5 years.12 Between ages 2 and 5 years, growth rates fornormal-birth-weight and VLBW children in the presentstudy were not significantly different, but between ages5 and 8 years, the VLBW children grew at significantlylower rates than did the normal-birth-weight children.These observations suggest that VLBW children as agroup not only do not catch up to their normal-birth-weight peers by age 8 years, but also may fall further behind between ages 5 and 8 years. However, there are individual exceptions to the average, helping to explainwhy more short and light VLBW children at age 2 yearsoutgrew those categories by age 8 years.Within the VLBW cohort, group 1 (ELBW) childrenwere significantly shorter at age 8 years than group 2(larger VLBW) children, but the weight ratios were notsignificantly different. Growth rates between ages 2 and5 years were not different between groups 1 and 2, butbetween ages 5 and 8 years, group 1 children had significantly smaller height increments, which would havecontributed to them being significantly shorter at age 8years. Therefore within the VLBW cohort, group 1 children were more disadvantaged in height than group 2children, and their increments in height were less.

For the clinician interested in treating short VLBW children with synthetic growth hormone, if the proportionsbelow the 5th and 10th percentiles for height at age 2 yearsare followed longitudinally, by age 8 years few remain inthe shortest categories. Obviously, age 2 years would betoo early to embark on growth hormone therapy for mostshort VLBW children; even age 5 years may be too early.The shortest VLBW children (below the 10th percentile) atage 8 years were offered an appointment for evaluation atan endocrine clinic; not all parents accepted this invitationbecause they or the child were not concerned. We do nothave any data on psychological problems specifically related to short stature in our children.

Not all variables in Table 1 were included in the logisticregression analyses. Cerebroventricular hemorrhage wasexcluded because not all children were scanned in thenewborn period (none of group 3 and almost half of group1). Seizures and nectrotizing enterocolitis were not included because they occurred so infrequently. It was notable that no health variables determined after birth, during the neonatal period or subsequently, were associatedwith a height or weight below the 10th percentile at age8 years in VLBW children. Similarly, social variables werenot associated with poor growth at age 8 years, a findingconsistent with that of Carmichael et al24 in a recent studyof growth to age 4 years in a socioeconomically poor urban Australian community. Not surprisingly, a lowerbirth-weight ratio was associated with a weight below the10th percentile at age 8 years, and a lower maternal heightwas associated with a height below the 10th percentile,

indicating that variables originating before birth arestronger determinants of growth failure in childhood thanany subsequent ill health after birth.

Because VLBW children are not catching up to theirnormal-birth-weight peers by age 8 years, and becauseELBW children are growing more slowly between ages 5and 8 years, we will continue to follow up the growth ofthese children, into adulthood.

This study was supported in part by the Health Department ofVictoria and the Royal Women's Hospital-3AW Clinical ResearchFoundation.

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Western pediatricians may find it difficult to believe that child death isan ordinary, expected, and routine event in many parts of the world. Arecent review, "Social Indifference to Child Death," describes poignantlythe death of a 3-year-old girl due to malnutrition, recurrent diarrhea, andvomiting. Her mother said, "Infants are like birds, here today, gonetomorrow. Alive or dead, it's all the same to them." The child was dressedin her white, holy communion dress and covered with white flowers before her funeral. On returning to visit the grave some time after the burial,the area had been cleared and the space given to twin infants. The 3-year-old girl's remains had been tossed into the deep well called the bone depository.

Scheper-Hughes N. Social indifference to child death. Lancet. 1991,'337:1144-1147.

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