pregnancy outcome at 24-31 weeks' gestation: neonatal ... · pregnancy outcome at 24-31...

Archives of Disease in Childhood, 1989, 64, 678-686

Pregnancy outcome at 24-31 weeks' gestation:neonatal survivorsU WARIYAR, S RICHMOND, AND E HEY

Regional Perinatal Mortality Survey, Northern Regional Health Authority, Newcastle upon Tyne

SUMMARY All surviving babies of less than 32 weeks' gestation born to mothers resident in theNorthern region in 1983 were assessed. No baby was lost to follow up, and 230 long termsurvivors were assessed when 2 years old, by a single observer. Among 248 neonatal survivors,severe disability was present in 10 of the 37 at 24-27 weeks' gestation (27%) and in 18 of the 211at 28-31 weeks' gestation (9%). On average the surviving babies required 27 days and seven daysof intensive care nursing respectively. Babies who were ventilated for more than two weeks andbabies who had neonatal fits had a poor prognosis. Because of postneonatal deaths only 20 of the230 long term survivors of <32 weeks' gestation were severely disabled (9%).Comparable data were obtained for all babies weighing 1500 g or less at birth, irrespective of

their gestational age. Severe disability was seen in eight of the 49 neonatal survivors (16%) whohad weighed 500-999 g at birth, and in 17 of the 171 survivors (10%) who had weighed 1000-1499 g.

The 10 neonatal survivors who had weighed exactly 1500 g at birth were all well. Only 18 of the212 long term survivors (8%) who had weighed 1500 g or less at birth were severely disabled.Because the period of gestation is the only variable known to the obstetrician before delivery,

and disability correlates better with gestation than birth weight, future studies should concentrateon relating morbidity, mortality, and the cost of neonatal care to gestation rather than weight atbirth.

There have been many publications about the longterm prognosis for low birthweight babies. Mosthave concerned the experience in a single hospital,and reported accumulated data over a number ofyears. Few have reported the outcome in anunbiased population of all the babies born tomothers living in a defined geographical area in adefined time. Fewer still have provided detailedanalyses of all the deaths as well as of disabilitiesamong survivors from such a cohort. No such studyhas managed to maintain contact with every survivorfor two years so that a single clinician could assessthe progress of every child consistently.A study has now been completed in the Northern

region of all very low birthweight babies born in1983. Comparable studies of children born before1980 had all reported outcome in terms of birthweight, but gestation is the only variable accuratelyknown to the obstetrician before delivery. Wetherefore report here the developmental progress ofevery baby born before 32 weeks' gestation in 1983,as well as the outcome for every neonatal survivorwho had weighed 1500 g or less at birth.

Subjects and methods

Background information had already been collected(for a parallel study of mortality) for every baby ofless than 32 weeks' gestation and every babyweighing 1500 g or less at birth born in 1983 to amother normally resident in the Northern region.'Approval for a special follow up survey was obtainedfrom each district's ethics committee. All thechildren were traced and seen by a single clinician(UW) for assessment on or about their secondbirthday (21-26 months after birth) in order to makethe assessments as consistent as possible. Informationfrom the general practitioners, health visitors, andlocal paediatricians was available to the doctorbefore he saw each family, but information aboutthe obstetric and neonatal background was onlyabstracted from the hospital case notes and enteredon a standard form after the assessment had beencompleted.

Objective measures of disability were obtained sothat this study could be compared with similarstudies, although precise testing can be difficult in

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Pregnancy outcome at 24-31 weeks' gestation: neonatal survivors 679

children only 2 years old especially if they are shy,restless, or uncooperative. Assessment included afull medical history followed by a complete clinicaland neurological examination, including anthro-pometric measurements and the recording of theblood pressure. A Griffiths's assessment2 3 wasmade to obtain a quantitative assessment ofdevelopmental progress. Stycar hearing testswere supplemented by free field audiometry in themore cooperative children, and binocular visualacuity was checked with Stycar tests; in half thechildren this was repeated for each eye separately.The visual fields were checked, and a cover test wasdone for latent squint. More detailed audiologicaland ophthalmic information was obtained on all thechildren with any significant impairment. The clinicalfindings were always discussed with the parents assoon as the assessment was complete, and arrange-ments made for further help to be obtained on thoseoccasions where this assessment brought a clinicalproblem to light for the first time.

Results

There were 39 350 registered births in the Northernregion in 1983; 395 of these babies were born before32 weeks' gestation. There were also 101 babies whowere born dead at 24-27 weeks' gestation and whosebirths were not registered. There were 49 registeredstillbirths, and 346 live births before 32 weeks'gestation. Eighty seven of the live born babies diedin the first week of life, 11 more died during the nextthree weeks, and 18 died later in infancy.' Therewere therefore 230 long term survivors from thiscohort two years after delivery (table 1).

POSTNEONATAL DEATHSThere were 18 postneonatal deaths (table 2). Eight

of these babies had clinical evidence of severeperinatal neurological impairment before death, andthis clinical assessment was supported by ultrasoundor necropsy evidence of severe parenchymal braindamage, or both, except in the one case where noultrasound or necropsy examination was under-taken. Six of the 18 babies died after leavinghospital, and only one of these had an impairmentthat looked as though it was likely to causedisability; all were dead within seven months ofdelivery.

LONG TERM SURVIVORSThe detailed developmental progress of the 230children still alive two years after birth is summa-rised in fig 1. Every child with a developmentalquotient of less than 70 also had other grounds forbeing classified as severely disabled. The develop-mental quotient of the children of more than 26weeks' gestation who had no motor or sensorydisability was normally distributed, but the babies of24-26 weeks' gestation tended to have a slightlylower developmental quotient-a finding that willcall for further scrutiny when the children reachschool age.

Severe disabilityCerebral palsy severe enough to hamper physicalactivity appropriate to the child's age was judged asevere disability, as was deafness severe enough towarrant a hearing aid (usually equivalent to ahearing loss of 50 dB or more in the better ear), andblindness or partial sight (usually equivalent to acorrected binocular visual activity of 6/60 or less). Adevelopmental quotient of less than 70 on theGriffiths's assessment scales was also accepted asevidence of severe disability. This threshold waschosen because it is three standard deviations below

Table 1 Mortality and morbidity in babies of 24-31 weeks' gestation

Gestation Deaths Survivors at the age of 2 years(weeks)

Born Neonatal Post- Severe Impairment Minor Normaldead deaths neonatal disability without impairment

(0-27 days) deathst disability

24 33* 17 1 (0) 0 0 0 125 29* 15 1 (1) 2 0 1 326 25* 14 1 (1) 2 1 1 827 14* 15 2 (1) 3 0 1 928 10 12 2 (1) 2 0 2 2229 12 8 2 (1) 2 3 4 2730 13 13 4 (2) 3 2 7 4731 14 4 5 (1) 6 2 7 62

Total 150 98 18 (8) 20 8 23 179

*Unregistered stillbirths; tnumber with neurodevelopmental impairment in parentheses.


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680 Wariyar, Richmond, and Hey

Table 2 Postneonatal deaths among babies of <32 weeks' gestation or weighing J1500 g at birth

Sex Mode of Reasondelivery delivered

24 660 F Breech Premature labour25 800 M Vertex Premature labour

26 1110 F Caesarean Abruption

27 980 M Vertex Abruption

27

2828

29

29

995

6701200

1190

1400

M

M

M

F

M

Breech

BreechVertex

Vertex

Vertex

Premature ruptureof membranes

Premature labourPremature rupture

of membranesPremature rupture

of membranesPremature labour

30 965 M Caesarean Toxaemia30 1300 M Caesarean Premature labour

30

3031

313131

31

1490

16601130

134013801400

1775

M

M

M

FM

F

M

Ver-tex

VertexCaesarean

VertexBreechVertex

Vertex

Premature ruptureof membranes

Premature labourAbruption

Premature labourPremature labourPremature rupture

of membranesMaternal factors

32 1280 M Vertex Premature labour33 1480 F Caesarean Toxaemia

Venti- Age atlation death(days) (days)

31 3148 48

25 118

16 36

18 41

30 17834 34

11 138

14 118

62 623 37

17 185

31 3732 103

_ 205- 181- 83

30 101

5 12916 44

Diagnosis

Neerotising enteroeolitis, ehronie lung damage; twinNecrotising enterocolitis, terminal candida septicaemia,

severe posthaemorrhagic hydrocephalus*Staphyloeoecal ventriculitis after shunt for

posthaemorrhagic hydrocephalus*Klebsiella meningitis: periventricular leucomalacia at

necropsy*Resuscitation failed after sudden apnoeic attack

Chronic lung damage after ventilation; twinPersistent seizures. No necropsy*

Home after 65 days; died of respiratory syncytialbronehiolitis

Home after 91 days; periventricular leucomalacia;died suddenly at home*

Ventilator dependent from birth; chronic lung damageDied after operation for necrotising enterocolitis.

Intracerebral haemorrhage with fits*Chronic lung damage after ventilation

Citrobacter septicaemia, intracerebral bleed*Home after 91 days: died after sudden apnoeic attaek.Twin

Home after 43 days: cot deathHome after 64 days: cot deathHome after 49 days: cot death

Staphylococcal meningitis while undergoing tap forposthaemorrhagie hydrocephalus*

Concealed birth; subdural haemorrhage, died of fits*Cardiac failure; also had rectal agenesis and cardiac defect

*Had severe perinatal neurological impairment.

the mean and identifies continuing serious develop-mental delay in later childhood with some certainty.We would have classified epilepsy uncontrolled bydrugs, chronic malabsorption and growth retardationdue to major bowel resection, the loss of a limb, or

the presence of a permanent stoma as severe

disabilities, but did not find any.

Twenty children were severely disabled, and mostof these children had more than one disability (fig1). Fifteen children had disabling cerebral palsy, and12 had developmental quotients of less than 70.Seven children were registered as blind or partiallysighted; in four cases this was caused by damage tothe central visual pathways, but in three there was

severe retinopathy of prematurity. The five childrenwith cerebral palsy as well as visual disability had thelowest developmental quotients in the study. Fourchildren were deaf enough to require hearing aids,but none of the deaf children had had serum

bilirubin concentrations of more than 225 itmol/l,and only one (a profoundly disabled child of 31weeks' gestation) had any features of cerebral palsy.Three children had serious epilepsy, but in each case

this was well controlled by drugs.

These definitions identify a group of children whohad cerebral palsy severe enough to interfere witheveryday motor activity, or sensorineural impair-ment severe enough to be likely to require specialeducational provision, or both. Nine children haddevelopmental quotients of less than 50. Pooroutcomes had been anticipated in some of thesechildren. The only surviving triplet baby (of 25weeks' gestation) required considerable resuscita-tion at birth and had early evidence of intracerebralbleeding on ultrasound scan followed by diffusecystic change (developmental quotient 30). Onechild had congenital myotonic dystrophy and a

developmental quotient of 38, and another had beenventilated for severe coliform meningitis at the ageof 5 days (developmental quotient 22). Four otherbabies, however, had remarkably uneventfulneonatal courses: two were ventilated for less thanfour days (developmental quotients 11 and 41) andtwo were not ventilated at all (developmentalquotients 8 and 41). Some disability had beenanticipated in the remaining two babies becausethere was ultrasound evidence of intracerebralbleeding (developmental quotients 10 and 18), but

Gestation Birth(weeks) weight

(g)


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* Disabling cerebral palsye Mild cerebral palsyb. Visually impairedA Hearing impaired+ Shunt for hydrocephalus

0 000 0o 00 o

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30

.I . ,1124 25

4110 11

26 27 28

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08 0 c0

00o 00

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CO GO00 0

0 80

00 0

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38

29

o Uncategorised mild developmental delayThree children without pronounced motor orsensory impairment had developmental quotients of

o between 70 and 79 when seen at the age of 2 years0000 (that is, quotients two to three standard deviations808 below normal). All had deprived backgrounds; in

>0° 0 addition, one child had been encased in plaster for)OO O 000 late diagnosed congenital dislocation of the hip forOO 0000 more than 12 months, one child's mother had

00 - suffered a long severe depression, and the third8 o0oo child came from a family where there had been child0 008 abuse. Two of the three children with develop-1° O mental quotients of 80 had also received little°ooo stimulation, and one had spent more than eight

0-0 months in hospital (fig 1). The effect of the0

0 environment on development becomes progressively0* more important with time, and some or all of these

children may need special educational provision indue course. A low assessment quotient at this age,however, may merely mean that the child was shyand uncooperative in unfamiliar surroundings whentested. All the children in this study will be reviewedagain at the age of 6 to monitor their growth,

1 22 18 8 validate the assessment of disability made at the age;,* of 2, and look for signs of poor motor coordination

30 31 and other important but subtle learning problems.Gestation (weeks)

Fig 1 Association between gestation and developmentalquotient in all the babies who survived to the ageof 2, showing the correlation with other sensorineuralimpairment. Numbers refer to individual developmentalquotients of babies scoring less than 60.

the neonatal courses of these two children did nototherwise differ from those of some of the childrenwho were much less disabled.

Impairment without disabilityEight children had impairment without disability:five had definite but mild cerebral palsy (usuallymild hemiplegia) and four had required ventriculo-peritoneal shunts because of posthaemorrhagichydrocephalus, but were otherwise well without anyimportant neurological disability. Only one had a

developmental quotient below 80 (fig 1).

Minor impairmentA further 23 children had minor impairments.Problems under this heading included squint(n= 17), growth retardation after resection of boweland temporary ileostomy (n=2), severe amnioticbands or talipes requiring operation (n=2), pro-nounced speech delay with probable conductivehearing loss (n=1), and longstanding ankylosis ofboth elbows (n=1).

Babies small for gestational ageThe distribution of birth weight by gestation in thiscommunity based study was similar to that recentlyreported for a hospital based study from Oxford.4Thirteen normally formed babies who were borndead had weights below the fifth centile at delivery,as did three babies who died shortly after birth. Tenbabies with weights below the fifth centile survivedthe neonatal period, though one died later of lungdamage after a period of prolonged respiratorysupport (table 1). The nine long term survivors werewell at two years, without any disability or impair-ment. Others have reported, however, that babiessmall for gestational age who weighed 1500 gor less at birth often perform poorly in school.6Similar findings have been reported in babies smallfor gestational age who were born at full term wherethere was sonar evidence that fetal growth hadstarted to falter before 27 weeks' gestation.7 It willbe particularly important, therefore, to reassessthese children after they have started school.

Predicting neonatal outcomeThere was only a marginal excess mortality amongboys, but 22 of the 28 neonatal survivors withdisability were boys, and a preponderance of boyshas been noted in other studies.8 Overt neonatalfits9 were also strongly correlated with severedisability: seven of the 17 neonatal survivors who

120

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0 90

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80

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4

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had fits in the first week of life died later in infancywith evidence of severe perinatal neurologicalimpairment, and five long term survivors are alsodisabled. One other baby survived with a mild lefthemiplegia; only four seemed entirely well when 2years old. Babies ventilated for up to two weekswere only slightly more likely to survive withdisability than babies not ventilated at birth (9%compared with 5%), but babies ventilated for morethan two weeks had a high risk of disability (table 3).There seemed to be no correlation between the

highest serum concentration of bilirubin recorded inthe neonatal period and the risk of disability amonglong term survivors. Thirty three survivors had hadserum bilirubin concentrations of 250 [imol/l or

more, but only two of these children were disabled:both had severe spastic quadriplegia and one was

also blind but neither was deaf. Two of the threechildren with disabling retinopathy of prematuritywere of less than 27 weeks' gestation and both hadreceived supplemental oxygen for more than 10weeks (this was also true, however, of 10 childrenwho had no visual problems at follow up); the thirdchild (of 30 weeks' gestation) with retinopathy ofprematurity had been ventilated for eight days andgiven supplemental oxygen for 14 days afterdeveloping meningitis when 5 days old.

HOSPITAL CAREFigure 2 shows how gestational age influenced theamount of hospital care received by the babies ofless than 32 weeks' gestation who died beforedischarge, and by the survivors. The times spentreceiving intensive care (respiratory support) andhigh dependency care are shown separately becausestaffing needs make such care particularlyexpensive.10 The babies of less than 32 weeks'gestation accounted for 6% of all admissions tospecial care units but 29% of all nursery cotoccupancy in the region during the year of the

survey. Three quarters of all the babies ventilated inthe region during the year were of less than 32weeks' gestation, and these babies accounted for84% of all non-surgical neonatal ventilator usage('ventilator nights'). Only 4% (two of 57) of theliveborn babies of 26-27 weeks' gestation and 27%(23 of 86) of liveborn babies of 28-29 weeks'gestation survived without sustained respiratorysupport (fig 2), but 58% (94 of 162) of babies of30-31 weeks' gestation survived without support, as

did 86% of the babies of 32-33 weeks' gestation.

SURVIVORS OF ANY GESTATIONAL AGE WHO WEIGHED

LESS THAN 1500 G AT BIRTH

A separate analysis was undertaken of the outcome

Gestation(weeks)

D

24-25 H

S

D

26-27 HS

D

28-29 H

S

D

30-31 HS

= Special care

0 High dependency

M Ventilated

F132

1 15777 120

2J22

59

*2 22

E J 1131

Proportion survivingwithout ventilation

= 2 | O%

=5

4%

=5s 27%

558 o

0 50 100 150Days

Fig 2 Association between gestational age andaverage hospital care needs of babies who died beforedischarge (D) and in the disabled (H) and non-disabled(S) survivors, with care classified in a comparable waywith previous costing studies. ' The numbers at the endof each histogram bar indicate the number ofbabies in each group.

Table 3 Correlation between ventilation dependency in days and the risk of severe disability in those who survivedfor 28 days

Outcome No of days ventilated

0 1-6 7-13 14-20 21-27 >28

No of survivors at 28 days 121 56 31 11 7 22No of later deaths:

Disabled 0 1 0 2 1 4Not disabled 3 0 1 2 0 4

No of disabled long termsurvivors 6 4 2 1 1 6

Percentage of neonatalsurvivors disabled 5 9 6 27 30 45

MIZI


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for all babies who had weighed 1500 g or less atbirth, whatever their gestational age. There werenine registerable births of less than 500 g, two at20-23 weeks' gestation, four at 24-31 weeks' gesta-tion, and three at more than 31 weeks' gestation, butnone of these babies survived the neonatal period.A further 470 babies weighed between 500 and1499 g at birth (table 4). Details of the postneonataldeaths are given in table 2. Nine babies of 24-31weeks' gestation and four babies of more than 31weeks' gestation weighed exactly 1500 g at birth.One baby was stillborn at 37 weeks' gestation, andtwo babies died with lethal malformations on thefirst day of life at 28 and 30 weeks' gestation,respectively. The 10 survivors were all well withoutdisability, when 2 years old.One hundred and eight babies (including 82

neonatal survivors) of 24-31 weeks' gestationweighed 1500 g or more at birth, and 96 babies(including 54 survivors) weighed less than 1500 g,although they were more than 31 weeks' gestation atbirth.

Discussion

Every neonatal survivor in this large regional studywas accounted for, and every child assessed by thesame observer when 2 years old. Some childrenproved difficult to trace, and others proved difficultto see for assessment though they were tracedwithout difficulty. The amount of disability in theselatter groups was much higher than in the 89% whowere contacted without difficulty,11 a finding that

Table 4 Outcome at the age of 2 of all babies weighing500-1499 g at birth who were born in the Northern regionin 1983, irrespective of period of gestation

Outcome Birth weight

500-999 g 1000-1499 g

No of babies born deadbefore 28 weeks' gestation 80 3

No of registered stillbirths 23 46No of neonatal deaths

(0-27 days) 61 37No of later deaths:

Disabled 2 5Not disabled 4 7

No of disabled long termsurvivors 6 12

No of other long termsurvivors 37 147

Percentage disability inlong term survivors 14 8

points to the importance of tracing and assessing allthe survivors in any study of this nature.

POSTNEONATAL DEATHEighteen of the 248 babies of less than 32 weeks'gestation who survived the neonatal period diedlater (7%). Six died suddenly, five after dischargefrom hospital; one neurologically impaired babyprobably died of a seizure shortly after discharge butthe other five deaths were unexplained, though onebaby did have some evidence of bronchopulmonarydysplasia at necropsy. It seems that the risk ofsudden infant death in babies born more than eightweeks early may be 10 times as high as in babiesborn at full term.'2 Most of the other postneonatalhospital deaths were caused by infection, chroniclung scarring after a period of respiratory support,or necrotising enterocolitis (table 2).

TWIN PREGNANCIESMortality among twins delivered before 32 weeks'gestation was slightly lower than in singletons ofcomparable gestation in this study' as it was in theNational Perinatal Mortality Survey of 1958.13 Theincidence of disability among survivors was also lessthan among singletons. This finding is in keepingwith other work, suggesting that when twin babiesare compared with singletons and matched forgestation a clear excess of cerebral palsy is only seenin comparatively mature twins.'4 The risk of fetal orearly neonatal death in a twin pregnancy of morethan 21 weeks' gestation was 10 times as high as itwas in singleton pregnancies in this study, largelybecause of the increased risk of premature labour.Forty six of the 413 twin pregnancies (11%) endedbefore 32 weeks' gestation in 1983, and 42 of 70(60%) of the perinatal mortality associated withtwin pregnancy occurred among these babies. In-deed, 53% of all fetal and early neonatal lossesoccurred before 29 weeks' gestation, including allbut four of the 19 neonatal deaths associated withproblems of prematurity. Even if there is any benefitin offering bed rest in twin pregnancies 5 it wouldseem to be illogical to delay it until 32 weeks'gestation.

COSTMuch concern has been expressed over the cost ofproviding medical care for babies as small as this,and studies from North America have suggested thatthe cost may outweigh the economic benefit forbabies weighing below about 1000 g (if this iscalculated in purely monetary terms). Costing exer-cises in this country have failed to define a particularbirth weight below which it is uneconomical to offersustained intensive care support, but they have


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identified that the average investment put intocaring for the babies who did not survive todischarge can be nearly as high as that put into thecare of survivors.10No attempt has been made to undertake a full

detailed costing of neonatal care in this study, but arealistic estimate can be obtained from a knowledgeof cot occupancy and the length of time for whicheach child required respiratory support or receivedother high dependency care. On the assumption thatthe care of the babies requiring respiratory supportcosts about three times as much as that of babiesonly requiring special care'( it can be seen that the110 babies who failed to survive to dischargeaccounted for only about 12% of the sum spent oncaring for all the liveborn babies of 24-31 weeks'gestation before discharge. If babies who failed tosurvive for at least a day after birth are discounted(as in previous costing studies) the average amountinvested in each of the 57 babies who did not survive

to discharge is still only a quarter of that invested inthe 236 babies who did. Only in babies of 30-31weeks' gestation did the care invested in the 16babies who survived more than a day but who failedto survive to discharge exceed the average spent onthe 140 babies who did survive to discharge.

Previous costing studies have failed to show anystrong correlation between cost and birth weight,'0but the data in fig 3 suggest that there is quite astrong correlation between cost and gestational age,and this is further strengthened when individual(rather than average) care costs are analysed. Thisis of course what would be expected, because verypremature babies are usually only robust enough fordischarge a week or so before they were due to beborn whatever their weight at birth. Thus the 25surviving babies born at 26-7 weeks' gestation (91days before term) went home, on average, 84 daysafter delivery and seven days before they were dueto be born (fig 2). Requirements for respiratory

- Severely disabled

Non-disabling impairmentMinor impairment

EIZI Normal survivors

2 31 7

24-25 _-~~~~~~~~~~~~~~~~~~~~~~~~~~< _5 6 8

26-274 7 13

28-29.Z.NI. :, I._1 27

30-31_ t- I

C

j36I.

mommoMr-7-7.1 77-7.: I I

516 J1 401-a

-I19

j

61

1

2 4 7

~ 1000-12497Jjjj0) 8 11a)

34 9 57

1749 9 22 3 5 23

1750 _ >1

L I I I I I I I I J0 10 20 30 40 50 60 70 80 90 100%

Fig 3 Disability and non-disabling impairment at 2 years in babies of24-31 weeks' gestation, showing the correlation withgestational age but the lack of correlation with birth weight.

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r.9 I a

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support and other high dependency care also variedinversely with gestation, with the disabled survivorsat each gestation requiring marginally more care andsupport than the non-disabled survivors (fig 2).

Previous costing exercises have all been under-taken in large referral centres, and have beeninfluenced by the biases caused by selective patientreferral, have reflected medical practice in a singlecentre, and have sometimes only measured costwhile in the referral centre rather than total cost todischarge. The broader approach adopted hereprovides a more accurate picture of the way in whichthe region's neonatal resources were used by thebabies in this study. Such costing exercises, how-ever, have their limitations. Many large unit costs(staff, hospital overheads, and so on) remain thesame irrespective of the number of children caredfor, or the amount of care invested in each patient.It will always seem cheaper to centralise the care ofall babies requiring high dependency care to a fewcentres in each region to maintain a high cotoccupancy, but such a calculation fails to allow forthe need for district hospitals to maintain certainminimum neonatal staffing levels whether theyundertake the care of babies requiring long termrespiratory support or not. The opportunity cost ofcentralising high dependency care (the scope forredeploying existing staff and facilities in otherways) may be quite small. The case for centralisingcare depends on the argument that such a policyimproves neonatal outcome.

OTHER STUDIESDirect comparison with other studies is impossibleas all previous population based follow up studieshave defined the group of children requiring followup by birth weight, and used birth weight ratherthan gestational age to analyse the results obtained.Information was therefore collected about all thebabies weighing 500-1500 g at birth who were bornin the region in 1983 (whatever their gestationalage). Of the children still alive 92% had no seriousdisability at the age of 2 years, a result that isbroadly in line with earlier English communitybased studies from south east London, Mansfield,Wolverhampton, and Liverpool16 of babies bornbetween 1963 and 1981, although each of thesestudies defined disability in a slightly different way.Some classified epilepsy controlled by drugs, asymp-tomatic posthaemorrhagic hydrocephalus controlledby a ventriculoperitoneal shunt, and minor degreesof cerebral palsy that did not interfere with everydayactivity, as evidence of 'disability', but these func-tional impairments (to use the terminology favouredby WHO17) often cause little disability. Neverthe-less it seems clear from the available data that

increased neonatal survival over the last 20 years hasnot been associated with any important change inthe proportion of long term survivors with seriousdisabilities.

PROGNOSISThe present study highlights the poor prognosis thatis associated with early neonatal fits, the increasedincidence of disability in babies requiring more thantwo weeks of respiratory support (which may bepartly due to a cross correlation with gestationalage, fig 2) and the pronounced excess of malesurvivors with disabilities.Outcome also seemed to be influenced by the

obstetric factor that precipitated delivery. Thechance of long term survival without disability insingleton babies of 24-31 weeks' gestation withoutmalformations who were alive at the onset of labouror delivery was higher when delivery was precipi-tated by pre-eclampsia (73%) or antepartumhaemorrhage (73%), than it was when spontaneousrupture of membranes before the onset of labour(60%), or spontaneous premature labour (52%),were the main obstetric factors. As the number ofbabies in each of these groups is comparativelysmall, the differences in prognosis may be a chancefinding; minor differences in mean gestational agemay be a further confounding factor. Neverthelessthere is a clear need for further studies of this natureto see if such differences are consistently seen.

Nearly a fifth (19%) of the neonatal survivorsafter spontaneous premature labour were severelydisabled, as were 13% of the neonatal survivors ofabruption placentae and other severe antepartumhaemorrhages. In contrast, only 3% of the neonatalsurvivors delivered because of pre-eclampsia, and6% of the survivors whose delivery followed spon-taneous rupture of membranes before labour wereseverely disabled. The mode of delivery had littlediscernible effect on mortality, or morbidity amongsurvivors, once the obstetric factor precipitatingdelivery and the gestational age were taken intoaccount.1The main finding of the present study is that

though disability in survivors is only poorly corre-lated with birth weight in babies born more thaneight weeks early, it is strongly correlated withgestational age. Severe disability was seen in sevenof the 32 long term survivors of 24-27 weeks'gestation (22%) and 13 of the 198 survivors of 28-31weeks' gestation (7%) (fig 3). This is in line with theresults of other community based studies that haveshown that neonatal survival in such babies corre-lates much more closely with gestation than withbirth weight.'8 The high incidence of disability inlong term survivors of less than 28 weeks' gestation


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also confirms the findings from the few hospitalbased reports in which prognosis was assessed interms of gestational age. We believe these findingsstrengthen the case for using gestational age ratherthan birth weight as the yardstick by which tomeasure outcome in all future studies of perinatalmortality and morbidity, even though analyses bybirth weight are, for the moment, the only way ofcomparing recently collected data with studies onbabies born before 1980.

Obstetricians urgently need better and moredetailed information on long term prognosis if theyare to make informed decisions about the manage-ment of mothers who require delivery, or whothreaten to deliver spontaneously, more than eightweeks before full term. Parents themselves alsoneed such information if they are to be concerned inand consulted about management when problems ofthis nature arise. At this stage the obstetrician willknow which is the primary factor complicating thepregnancy, and will have a good idea of the baby'sgestational age, but will only have an imperfectassessment of the baby's weight.These considerations point to the logic of report-

ing both short and long term outcome in terms ofgestational age rather than birth weight. Resistanceto such an idea has usually been based on a feelingthat, though birth weight had been documented withsome precision, information on gestation is neces-sarily imprecise. Though this is undoubtedly true,the need for precision can be exaggerated becausechildren are usually subdivided into 100 g (or 250 g)birth weight groups for analytical and prognosticpurposes. Furthermore, the advent of ultrasoundscanning and of other techniques for dating preg-nancies'9 have now increased the accuracy withwhich gestational age can be determined in earlypregnancy. The case note review undertaken duringthe present study showed that serious errors oftencrept into the calculation and documentation ofgestational age, but it also showed that the variousprimary criteria used to assess gestational ageseldom gave estimates that differed by more than 10days.We conclude that although the routine docu-

mentation of gestational age at delivery is oftenunreliable at present this is not because precision isimpossible,but because the need for precision is notrecognised. As data continue to accumulate showingthat gestational age rather than weight is the mostpowerful predictor of mortality and morbidity atbirth in preterm babies, the importance of docu-menting gestation properly and the value of analysinglong term outcome by gestational age, shouldbecome more generally recognised.

This study would not have been possible without the help that theregion's paediatricians gave by retrospectively tracing the survivingchildren. We also owe a deep debt to the families of the children inthe study. We are particularly grateful to Mrs B Gibson for her skilland commitment in gaining the cooperation and trust of thefamilies, and in tracing those who had moved; it was herpersistence and dedication that finally ensured that no child waslost to follow up. Dr Wariyar was a research registrar funded by theRegional Health Authority at the time of the study.

References

Wariyar U, Richmond S, Hey E. Pregnancy outcome at 24-31weeks' gestation: mortality. Arch Dis Child 1989;64:670-7.

2 Griffiths R. The abilities of young children. London: ChildDevelopment Research Centre, 1970.

3 Griffiths R. The abilities of babies. Amersham: Association forResearch in Infant and Child Development, 1954.

4 Yudkin PL, Aboulfa M, Eyre JA, Redman CWG, WilkinsonAR. Influence of elective preterm delivery on birthweight andhead circumference standards. Arch Dis Child 1987;62:24-9.Yudkin PL, Aboulfa M, Eyre JA, Redman CWG, WilkinsonAR. New birthweight and head circumference centiles forgestational ages 24-42 weeks. Early Hum Dev 1987;15:45-52.

6 Francis-Williams J, Davies PA. Very low birthweight and laterintelligence. Dev Med Child Neurol 1974;16:709-28.

7 Parkinson CE, Wallis S, Harvey D. School achievement andbehaviour of children who were small-for-dates at birth. DevMed Child Neurol 1981;23:41-50.

8 Yu VYH, Loke HL, Bajuk B, Szymonowicz W, Orgill AA,Ashbury J. Prognosis for infants born at 23 to 28 weeksgestation. Br Med J 1986;293:1200-3.

9 Watkins A, Szymonowicz W, Jin X, Yu VVY. Significance ofseizures in very low-birthweight babies. Dev Med Child Neurol1988;30:162-9.

0 Sandhu B, Stevenson RC, Cooke RWI, Pharoah POD. Cost ofneonatal intensive care for very-low-birthweight infants. Lancet1986;i:600-3.Wariyar U, Richmond S. Morbidity and preterm delivery:importance of 100% follow-up. Lancet 1989;i:387-8.

12 Yu VYH, Watkins A, Bajuk B. Neonatal and postneonatalmortality in very low birthweight infants. Arch Dis Child1984;59:987-9.

3 Butler NR, Alberman ED. Perinatal problems. Edinburgh:Churchill Livingstone, 1969:131.

'4 Alberman ED. Cerebral palsy in twins. Guy's Hospital Report1964;113:285-95.

15 Saunders MC, Dick JS, Brown IMcL, McPherson K, Chalmers I.The effect of hospital admission for bedrest on the duration oftwin pregnancy: a randomised trial. Lancet 1985;ii:793-5.

16 Powell TG, Pharoah POD, Cooke RWI. Survival and morbidityin a geographical defined population of low birthweight infants.Lancet 1986;i:539-43.

'' World Health Organisation. International classification of im-pairments, disabilities and handicaps. Geneva: World HealthOrganisation, 1980.

18 Verloove-Vanhorick SP, Verwey RA, Brand R, BennebroekGravenhorst J, Keirse MJNC, Ruyns JH. Neonatal mortalityrisk in relation to gestational age and birthweight. Lancet1986;i:55-7.

9 Whittaker PG, Lind T, Lawson JY. A prospective study tocompare serum human placental lactogen and menstrual datesfor determining gestational age. Am J Obstet Gynecol 1987;156:178-82.

Correspondence to Dr U Wariyar, Princess Mary MaternityHospital, Great North Road, Newcastle upon Tyne NE2 3BD.

Accepted 18 November 1988


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