ORIGINAL RESEARCH * NOUVEAUTES EN RECHERCHE

Is perinatal carein southwestern Ontario regionalized?

M. Karen Campbell,*tt PhD; Graham W. Chance,*t MB, FRCPC; Renato Natale,* MD, FRCSC;Nancy Dodman,§ RN; Elaine Halinda,* RN; Linda Turner,t MEd

Objective: To determine whether perinatal care in southwestern Ontario is regionalized,to identify trends over time in referral patterns, to quantify trends in perinatal deathrates and to identify trends in perinatal death rates that give evidence of regionalization.Design: Cohort study.Setting: Thirty-two hospitals in southwestern Ontario (1 level III, 1 modified level IIIand 30 level II or I).Patients: All pregnant women admitted to the hospitals and their infants.Main outcome measures: Antenatal and neonatal transfer status, live-born with dischargehome alive from hospital of birth, stillborn, and live-born with death before discharge.Results: Between 1982 and 1985 the antenatal transfer rate increased from 2.2% to 2.8%(p < 0.003). The proportion of births of infants weighing 500 to 1499 g increased from49% to 69% at the level III hospital. The neonatal transfer rate increased from 26.2% to47.9% (p < 0.05) for infants in this birth-weight category and decreased from 10.2% to7.1% (p < 0.03) for infants weighing 1500 to 2499 g. The death rate among infants oflow birth weight was lowest among those born at the level III centre and decreased at allcentresbetween 1982 and 1985.Conclusions: Perinatal care in southwestern Ontario is regionalized and not centralized;regionalization in southwestern Ontario increased between 1982 and 1985.

Objectifs : Preciser si les soins de perinatalite dans le Sud-Ouest de l'Ontario sontregionalises, identifier les tendances chronologiques des profils d'aiguillage, quantifierles tendances des taux de mortalite perinatale et preciser les tendances des taux demortalite perinatale susceptibles de faire la preuve de la regionalisation.Conception: Etude de cohortes.Cadre: Trente-deux h6pitaux du Sud-Ouest de l'Ontario (1 de niveau III, 1 de niveau IIImodifie et 30 de niveaux II ou I).Patients : Toutes les femmes enceintes admises aux h6pitaux et leurs nouveau-nes.Principales mesures des resultats : Taux de transfert antenatal et neonatal, vif-nes enconge d'h6pital, mort-nes et vif-nes decedes avant le conge.Resultats: Entre 1982 et 1985, le taux de transfert antenatal est passe de 2,2 % a 2,8 %(p < 0,003). La proportion des naissances d'enfants pesant de 500 a 1 499 g a augmentede 49 % a 69 % a l'h6pital de niveau III. Le taux de transfert neonatal est passe de26,2 % a 47,9 % (p < 0,05) chez les enfants dans cette categorie de poids a la naissance et

From the departments of*Obstetrics and Gynaecology, tPaediatrics, and tEpidemiology and Biostatistics, Lawson Research Institute,University of Western Ontario, and §the Periplatal Outreach Program, St. Joseph's Health Centre, London, Ont.

Reprint requests to: Dr. M. Karen Campbell, Lawson Research Institute, University of Western Ontario, 268 Grosvenor St., London, ONN6A 4V2

CAN MED ASSOC J 1991; 144 (3) 305- For prescribing information see page 356

decru de 10,2 % a 7,1 % (p < 0,03) chez les nouveau-nes de 1 500 a 2 499 g. Le taux demortalite chez les nouveau-nes de faible poids a la naissance etait le moins eleve chezceux nes au centre de niveau III et a diminue a tous les centres entre 1982 et 1985.Conclusions: Les soins perinataux dans le Sud-Ouest de l'Ontario sont regionalises etnon centralises; la regionalisation dans cette region a augmente entre 1982 et 1985.

E ffective regionalization of perinatal care re-sults in appropriate transfer of pregnantwomen and newborns at high risk to a region-

al centre, with patients at low risk being cared for incommunity hospitals.' It is assumed that the qualityof care provided in community hospitals is main-tained partially by ensuring that enough births con-tinue to take place in these facilities and thusensuring a good level of expertise among staff.'Centralized perinatal care results in a shift of ser-vices to a central location. Possible consequences ofcentralization include the closure of some smallerunits and loss of experience at smaller hospitals thatremain open; personnel at these units may then beunable to handle perinatal crises when they arise.

Level I facilities can manage births with nosignificant identifiable risk. Level II facilities pro-vide level I care for the local population and alsohandle selected high-risk situations, including pre-mature labour at 32 or more weeks' gestation,uspected neonatal sepsis and any other problemsthat cannot be dealt with by a level I facility but donot require level III care. Level III regional perinatalcentres provide level I and II care for the localpopulation and also receive transfers of pregnantwomen and newborns at high risk.' Common indica-tions for transfer to a level III facility are given in

laDle indiications for trarsie e.taeIi -;cso'ta

Antenatal t,ransfef-L.-abouri threatened la -)^

gestatiorPremat; - 'uptulre of mernorcine_; : et K

gestati'rrSevere pregnancy-induced Fr y>ertert*.*Severe antepartum bleedingSevere growth restrictiorMaternal renal diseaseRhesus mmunizationAny rmiaternal life-threateniro'c d!seasFKnown fetal malformationindicatiorn for intervention aoowiatDoi an 8deliveryevf ;obstructed labour, fetal distress during abour

Neonatal transferBirth before 36 weeks' gestation at a iev& certre

before 32 weeks' gestatior, at a eve rii tetri-Birth weight less than 1500Respiratory distress, neonatal seps;L:...asphyxia

Symptornatic congenital rieart diseaseSerious, surgically amenable malformaticn-SerioLsS metabolic disordeNeed for total parenterall -1 'Need fi'- assisted ventiIatir'-l - -

Table 1. Modified level III centres, which are notuniversity based and do not have resident coverage,can handle many of the situations requiring level IIIcare with the exception of newborns of less than 28weeks' gestation or with a birth weight under 1000 g.

Numerous studies have shown that death ratesfor infants of low birth weight are lowest when birthoccurs in a centre able to provide neonatal intensivecare from the moment of birth.2'5 Since regionaliza-tion diverts the cases at highest risk to level IIIcentres, one would expect that, as programs ofregionalized care become established, death rateswould decrease faster in community hospitals thanin level III facilities. This has been shown to be thecase in Nova Scotia,6 Alberta7 and Ontario.8

In diverting high-risk cases from communityhospitals to tertiary care centres it is preferable notto divert low-risk cases. This is imperative in Ontar-io, where some patients may live a great distancefrom the nearest large hospital. Furthermore, keep-ing pregnant women at low risk in their own commu-nities minimizes disruption of families, ensures con-tinuing cooperation of practising physicians in com-munity hospitals9 and minimizes the overall costs ofregionalization. Programs of regionalized care inNova Scotia,6 Massachusetts'0 and Illinois" havebeen shown to divert high-risk cases to tertiary carecentres while not diverting low-risk cases.

The Ontario Ministry of Health has been en-couraging regionalization of perinatal care in theprovince since 1972.' 2 Regional perinatal advisorycommittees, in collaboration with the Ministry ofHealth, have developed a more efficient system oftransfer of pregnant women and neonates needingtertiary perinatal services. The provincial perinatalbed registry provides information on the availabilityof space in level III centres throughout the province,and transfers may occur between regions within theprovince. In addition, when all the perinatal beds inOntario are full, transfer out of the province occurs.

The success of regionalization of perinatal carein Ontario has been shown with provincial surveil-lance data;8 however, there are no detailed studies ofreferral patterns and use of tertiary care centres inthe province. We performed a study to determinewhether perinatal care in southwestern Ontario isregionalized, as measured by appropriate selection ofpatients for transfer to the regional level III centre,to identify trends over time in regional referralpatterns, to quantify trends in perinatal death ratesin the region and to identify any evidence of

306 CAN MED ASSOC J 1991; 144 (3)

regionalization of perinatal care suggested by trendsin perinatal death rates.

Southwestern Ontario is served by 1 level III, 1modified level III, 4 level II and 28 level I hospitalsproviding perinatal care. Since 1980 regionalizationof care has been encouraged through voluntaryparticipation in a perinatal outreach educationalprogram.'3 As part of the program a team comprisingan obstetrician, a nurse and a neonatologist visitseach hospital at least once a year to present topics ofperinatal care and review outcomes of patientsreferred to the level III centre. A program of nursingeducation is also provided, one objective of which isto minimize the potential for adverse outcomes ofbirth in community hospitals through increasedprediction and superior management of perinatalcomplications. Transfer is encouraged for womenconsidered at risk for having a newborn whose needswould exceed the resources available locally. Inaddition, the educational program provides informa-tion on the management and stabilization duringtransfer of newborns at high risk. By 1985 annualvisits were being made to all but 2 of the 33level I, level II and modified level III hospitals inthe region.

We hypothesized (a) that there is effective re-gionalization of perinatal care in southwestern On-tario and that patients would be shown to have beenappropriately selected or not selected for transfer tothe tertiary care centre. We also hypothesized thatbetween 1982 and 1985 there would have been(b) an increase in the rates of antenatal transfer,(c) a decrease in the frequency of births of infants ofvery low birth weight in community hospitals and(d) minimal change in the place of birth for infantsof normal birth weight and (e) that death rates forinfants of low birth weight would have decreasedmost among those born at smaller hospitals. Ifproven, hypotheses a, b and c would provide evi-dence of regionalization but would not conclusivelyrule out the possibility of centralization. Hypothesisd would demonstrate regionalization but not central-ization. Hypothesis e would imply that the place ofbirth is shifting toward the tertiary care centredisproportionately for those at highest risk. Thiswould provide evidence of regionalization and notcentralization.

Methods

This study received ethics approval from theHealth Sciences Review Board for Research Involv-ing Human Subjects at the University of WesternOntario, London. The level III hospital and 31 of the33 modified level III, level II and level I hospitalsgranted permission to review the records of pregnantwomen admitted in 1982 and 1985 (25 892 births).

Information was collected from hospital deliveryroom books. For 31 hospitals (the tertiary carecentre and 30 other hospitals) information was alsocollected from the hospital charts of the women andthe neonates.

For all births at the study hospitals the birthweight, date of birth and outcome were noted.Outcome was defined as antenatal and neonataltransfer status, live-born with discharge home alivefrom hospital of birth, stillborn, and live-born withdeath before discharge. For the first category neo-nates were tracked to ensure that the ultimateoutcome (death or survival) was known.

To address selection for antenatal transfer infor-mation was collected for those who had been admit-ted to one of the 31 level I, level II or modified levelIII hospitals but had been transferred before birth.The gestational age at the time of transfer, thedestination and the reason for transfer were noted.All transfers were recorded whether or not thedestination was in southwestern Ontario.

To address nonselection for transfer the follow-ing additional information was collected at the 30community hospitals where maternal charts werereviewed. For stillbirths, neonatal deaths and neona-tal transfers the research nurse reviewed the mater-nal chart to determine whether antenatal transferhad been indicated (according to the criteria ofTable 1). If transfer had been indicated the nursereviewed the chart to determine whether it had beenpossible. Transfer was considered not possible ifbirth was imminent or if weather conditions pre-vented transport. For neonatal deaths the neonatalchart was reviewed to determine whether neonataltransfer had been indicated and, if so, possible.Neonatal transfer was considered not possible if theinfant had died so soon after birth that transfercould not be done. The data for 1982 and 1985 werenot compared because of inherent biases in such acomparison. Instead, criteria appropriate to eachyear were applied. The indications for transfer speci-fied in Table 1 were applied rigidly for 1985;however, for 1982, infants under 24 weeks' gestationwere not considered candidates for transfer owing totheir almost certain death.

Data analysis

We compared the numbers of pregnant womentransferred using contingency table x2 analysis todetermine whether the rate of transfer and thecause-specific rate of transfer had changed. We usedall pregnancies as the denominator for transfer rates.A more ideal denominator would have been allwomen eligible for transfer; however, this numberwould have been known only if all the maternalcharts had been reviewed.

CAN MED ASSOC J 1991; 144 (3) 307

The trend over time in level of hospital of birthby birth weight and in neonatal transfer rate by birthweight and level of hospital of birth were investigat-ed by means of stratified contingency tables with x2analysis. The x2 statistic was partitioned to test theheterogeneity of trends among subgroups and toassess the statistical significance of trends withincombined subgroups.

We analysed outcome by means of multinomiallogistic regression analysis. Outcome was regarded asa multinomial variable (live-birth and survival todischarge, live-birth with death before discharge andstillbirth). The influence of level of hospital of birth,birth weight, year of birth and the interactions ofthese factors were investigated. The intent of thelogistic regression analysis was not to build a modelof perinatal mortality but, rather, to test hypothesisd by searching for an interaction between trend overtime and place of birth.

Stratification by level ofhospital ofbirth

Each category of hospital is heterogeneous, par-ticularly the level I category, which contains hospi-tals of a wide range of sizes. Between 1982 and 1985one of the hospitals changed from a level II to amodified level III centre, and another changed froma level III to a level II centre. We included the datafrom these two hospitals in the level II category topreserve the confidentiality promised these hospitalswhen they consented to participate in the study.Furthermore, inclusion of these hospitals in the levelII category prevented overstratification of the data.This was an a priori decision that, if it were to biasthe study findings, would bias against the studyhypotheses.

Results

The proportion of pregnant women admitted toa level I or II hospital who were transferred beforedelivery increased from 2.2% (262) in 1982 to 2.8%(326) in 1985 (p < 0.003). This increase was attribut-able to a rise of 38% in the rate of transfer of womenwith labour or threatened labour before 37 weeks'gestation (from 0.72% to 0.99%) (p = 0.024) and to arise of 115% in the rate of transfer of women withhypertension or toxemia (from 0.20% to 0.43%) (p =0.002). There was also an increase of 775% in therate of transfer for induction or failed induction(from 0.008% to 0.07%) (p = 0.018), but the numbersinvolved were small (one in 1982 and eight in 1985);this change thus was not an important cause of theoverall increase in transfer rate. The rate of transferfor any other reason or group of reasons did notchange significantly between 1982 and 1985. Otherfrequent reasons for transfer included obstructedlabour, antepartum hemorrhage and problems asso-ciated with the amniotic cavity and membranes (e.g.,prolonged rupture of the membranes and oligohy-dramnios). Less frequent reasons included multiplepregnancy, fetal or placental problems, abnormalityof the uterus or cervix, malpresentation and indica-tions of asphyxia. In the two study years there wereno antenatal transfers for reasons that could not becategorized as clinical indications for transfer (i.e.,there were no social reasons for transfer).

Table 2 shows the location of birth by birthweight. The level of hospital of birth changed signifi-cantly between 1982 and 1985 for each birth-weightcategory (p < 0.008). The magnitude of the changewas largest for birth weight less than 2000 g and wassmall for birth weight greater than 2500 g.

Table 2: Location of birth by birth weight

Birth weight, g;year

500-99919821985

1000-149919821985

1500-199919821985

2000-2499

Level of hospital of birth.no. (and %) of births

I -i 0i5 (5.71

9 (8.6)5 (4.1 .

24 (13.4)11 (5.8)

38 (42.2)23 (26.1)

43 (41.3)32 (26.0)

90 (50.3)68 (36.0)

sf otaerShift* of,l births

43 (47.8)60 (68.2)

52 (50.0)86 (69.9)

65 (36.3)110 (58.2)

1982 111 (19.4) 297 (52.0) 163 (28.5)1985 97 (17.2) 254 (45.1) 212 (37.7) 325001982 5272 (33.7) 6984 (44.7) 3379 (21.6)1985 4952 (31.3) 7013 (44.3) 3878 (24.5)

.he prooortionaf nnnbease n te number of births at the level Ill centre between 1982 and 1985,

42.7

39.8

388

04-I' 2?\

60.3

32.3

12.9

563

t K 6351. 843

308 CAN MED ASSOC J 1991; 144 (3)

The proportion of live-born infants of low birthweight (less than 2500 g) who were transferredneonatally is shown in Table 3. There was anincrease in the frequency of transfer among infantsweighing 500 to 1499 g (p < 0.05; no evidence ofheterogeneity between levels) and a decrease in thefrequency of transfer among those weighing 1500 to2499 g (p < 0.03; no evidence of heterogeneitybetween levels). Although the small number of in-fants in each birth weight stratum precluded analysesof finer birth-weight categories, qualitative examina-tion of such categories confirmed that the trendswere consistent among subgroups.

Review of all stillbirths, neonatal transfers andneonatal deaths showed that for 4 (3%) of the 135

stillborn infants and 11 (2%) of the 551 infants whoeither died neonatally or were transferred antenataltransfer should and could have been done. Of the 91live-born infants who died before discharge 7 (8%)should and could have been transferred neonatally.

Table 4 shows the rates of stillbirth, live-birthwith death before discharge and survival to dis-charge by level of hospital of birth for infants of lowbirth weight. The data for infants with fatal anoma-lies and those lost to follow-up were excluded. Deathrates decreased between 1982 and 1985, and thestatistical significance of this finding was confirmedby multinomial logistic regression (Table 5). Thedecrease appeared to be largest for level I hospitals;however, this observation failed to achieve statistical

CAN MED ASSOC J 1991; 144 (3) 309

Table 3: Rates of neonatal transfer to level Ill hospital amonglive-born infants of low birth weight (less than 2500 g)

Level of hospital of birth;no. (and %) of infants

Birth weight, g;year I If Total

500-14991982 6 (66.7) 10 (19.2) 16 (26.2)1985 7 (77.8) 16(41.0) 23(47.9)

1500-24991982 32 (25.0) 21 (5.5) 53 (10-3)1985 17 (16.0) 13 (4.1) 30 (7.1)

Partitioned x2 analysis of this table showed no interaction of level of hospital ofbirth with year (i.e., the trend over time was similar for level I and 11 hospitals), asignificant increase in the transfer rate for infants weighing 500 to 1499 g (p <0.05) and a significant decrease in the transfer rate for infants weighing 1500 to2499 g (p < 0.03).

Table 4: Outcome among infants of low birth weight (excluding those with fatal anomalies and those lost tofollow-up)

Level of hospital of birth; no. (and %) of infants

I 11 IlBirth weight, g;outcome 1982 1985 1982 1985 1982 1985

500-1499Stillbirth 9 (52.9) 1 (12.5) 27 (36.5) 14 (28.6) 17 (19.5) 13 (9.4)Death beforedischarge 4 (23.5) 2 (25.0) 21 (28.4) 7 (14.3) 24 (27.6) 19 (13.7)Survivalto discharge 4 (23.5) 5 (62.5) 26 (35.1) 28 (57.1) 46 (52.9) 107 (77.0)Total 17 8 74 49 8 139Total excluded

Fatal anomalies 1 0 4 5 8 7Lost to follow-up 0 2 3 1 0 0

1500-2499Stillbirth 6 (4.5) 2 (1.9) 10 (2.7) 3 (0.9) 8 (3.6) 3 (1.0)Death before discharge 3 (2.3) 1 (0.9) 7 (1.9) 1 (0.3) 0 (0.0) 5 (1.6)Survival to discharge 124 (93.2) 105 (97.2) 360 (95.5) 313 (98.7) 215 (96.4) 307 (97.5)Total 133 108 377 317 223 315Total excluded

Fatal anomalies 2 0 5 3 5 7Lost to follow-up 0 0 5 2 0 0

significance. This may have been due to lack ofpower stemming from the small number of births ofinfants of very low birth weight at level I hospitals.

In Table 5 the column "Death before discharge"represents the effect of level of hospital of birth,birth weight and year of birth on the odds of deathbefore discharge relative to the odds of survival. Thecolumn "Stillbirth" represents the effect of thesefactors on the odds of stillbirth relative to the oddsof survival. An odds ratio may range from 0 toinfinity. For main effects an odds ratio less than 1implies that the factor has decreased the odds of theadverse outcome, whereas an odds ratio greater than1 implies that the factor has increased the odds ofthe adverse outcome. An odds ratio of 1 implies noeffect.

The odds of death before discharge decreasedbetween 1982 and 1985 (odds ratio 0.045), de-creased with increasing birth weight (odds ratio0.006) and decreased with increasing level of hospi-tal of birth (odds ratio 0.353). The odds of stillbirthdecreased with increasing birth weight (odds ratio0.007) and decreased with increasing level of hospi-tal of birth (odds ratio 0.157). The effect of year ofbirth was large (odds ratio 0.289) and would havebeen highly significant clinically had it been signifi-cant statistically. The lack of statistical significancemay have been due to a lack of power stemmingfrom the small numbers of stillbirths.

Discussion

In our study we found that the reasons forantenatal transfer to a level III centre were clinicallyappropriate. The frequency of antenatal transferincreased between 1982 and 1985, owing mainly toan increase in the rates of transfer for labour orthreatened labour before 37 weeks' gestation and for

abie 5. Multinomia' ~Jgst.C regression of deathi_)crESpital cit birth

hypertension or toxemia. Because we used all preg-nancies as the denominator for transfer rates, thereare two possible explanations for this trend: thefrequency of early labour and of hypertension ortoxemia increased, or more women with these condi-tions were identified and transferred in 1985 than in1982. Clearly, the latter is a more plausible explana-tion. A definitive test of this hypothesis would beprovided only by a study in which the number ofwomen transferred was considered as a proportion ofall those eligible for transfer. We could not measurethis denominator, as a review of all maternal chartswould have been prohibitively expensive. Our studymay have underestimated the frequency of antenataltransfer since we included transfers after admissionto community hospitals but not transfers from emer-gency departments or private physicians' offices.Also, antenatal consultations were not considered inour study.

The data on the location of birth by birth weightare not subject to this underestimate since theyrepresent the local population served by the tertiarycare centre, patients transferred from referring hos-pitals, patients transferred from referring physicians'offices and patients who self-selected the centre. Thelarge increase in the proportion of births of infantsof low birth weight at the tertiary care centreindicates that more women at high risk were trans-ferred to the level III centre in 1985 than in 1982.The smaller increase in the proportion of births ofinfants weighing over 2500 g at the tertiary carecentre may imply a degree of centralization. Howev-er, it may also be a result of a secular trend inconsumer preference, the antenatal transfer ofwomen identified as being at high risk who gavebirth to infants of normal birth weight at low or highrisk (e.g., multiple pregnancy or congenital anomaly)and the transfer of "level II" patients to the tertiary

against year of birth. birth weight andreve-

Outcome; odds ratio (and 950/c confidence limits

Death t efore discharge p Stillbirth

Main effectsYearBirth weightevel of hospital

fit birth:rll-eractions

.ear rirthveig ht

,'ear level ofhospital ofb rth

Birth weight - leveof hospital;f birth

0.045 (0.003. 0.970)0.006 (0.001. 0.756)

0 353 (0.077. 1 63)

256 0771. 8.50)

;5-1 1 0.691. 3.29)

3i 4772X 2.53)

0.05 0.289 (0.030, 2.80)0.001 0.007 (0.001, 0.050)

0.20 0.157 (0.037, 0.670)

0.15 0.980 (0.368, 2.61;

0.30 1.083 (0.554. 2.13)

2.226(1 14.4.35.1

310 CAN MED ASSOC J 1991; 144 (3)

0.00'

L.--

:, :.-t I,,

care centre from facilities for which that centrefunctions in a level II capacity (because of geograph-ic proximity). The shift in place of birth for infantsweighing over 2500 g was much smaller than theshift for those of low birth weight, which indicatesthat it is unlikely that a great deal of centralizationoccurred.

The rate of neonatal transfer for infants weigh-ing 500 to 1499 g increased between 1982 and 1985.This may have been due in part to the higher rate ofsurvival among live-born infants, which may in turnreflect an increased ability of the level I and IIhospitals to stabilize the condition of these newbornsfor transport. The increased rate of neonatal transfermay also have been due in part to an increasedtendency to refer the surviving infants in this birthweight category, given that all else was equal.

The rate of neonatal transfer for infants weigh-ing 1500 to 2499 g decreased between 1982 and1985. One possible explanation for this trend is thatthe community hospitals have increased ability andconfidence in the care of infants in this birth-weightcategory. One of the aims of the outreach education-al program has been to improve the ability of level IIhospitals to care for infants in this category and toencourage them to retain them. The program in-cludes a nurse interchange program in which nursesfrom the level II centres have rotated positions withnurses at the level III centre to upgrade theirknowledge. Alternatively, increased rates of antena-tal transfer may have resulted in a "lower-risk"population among the infants born at communityhospitals, and these infants are less likely to haveneeded transfer. A combination of these explana-tions is likely.

For most of the infants with poor clinicaloutcomes who were born at a community hospitaleither the need for transfer co'uld not have beenpredicted or the infants could not have been trans-ferred. This observation is subject to biases owing tothe retrospective nature of the data collection. It ispossible that indications of maternal risk were notnoted in the chart, which would result in underesti-mation of the number who should have been trans-ferred. Conversely, it is possible that an individualphysician had a reason not to transfer a patient anddid not note it in the chart, which would result inoverestimation of the number who could be trans-ferred. The assessment of whether transfer shouldhave been done and could have been done was madeby an observer who was aware of the study hypothe-ses, and this may also have caused a bias. However,these biases are unlikely to have created inaccuracieslarge enough to nullify the conclusion that most ofthe infants who experienced adverse events associat-ed with birth at a smaller centre could not have beentransferred to a larger centre.

It is not possible to investigate relationshipsbetween transfer status and outcome. There is astrong bias built into such associations. Specifically,those at greatest risk for death do not survive to betransported, and, among infants of very low birthweight, one would inevitably find higher neonataldeath rates for those retained than for those trans-ferred.

Not surprisingly, we found that the death ratesamong infants of low birth weight were lowest forthose born at the level III centre. We also found thatdeath rates decreased at all centres between 1982and 1985, although the decrease was statisticallysignificant only for deaths before discharge and notfor stillbirths. We had hypothesized that the decreasein death rates between 1982 and 1985 would begreatest for infants born at the smaller hospitals.Evidence of this trend would be found in a signifi-cant interaction between time and level of hospitalof birth, with birth weight controlled for, in mul-tinomial logistic regression analysis. This trend wasclearly not present for stillbirths. For infant deathsbefore discharge examination of the data suggestedthe existence of this trend, but it was not statisticallysignificant. There are several possible reasons whythe hypothesized interaction did not achieve statisti-cal significance. First, the trend may not be linearamong levels and therefore may not be detectablewith a linear model. Second, there may have beeninsufficient power to detect the interaction; thelargest "effect size" visible in Table 4 occurs instrata with the smallest number of subjects. Third,the trend may be partially masked by the heterogen-eity of hospital categories. As a post-hoc analysis wewithdrew the data for the modified level III hospitalfrom the level II category and repeated the analysis.This manoeuvre did not substantially change thefinding.

We conclude that perinatal care in southwesternOntario is regionalized and not centralized. Thisconclusion is based on the following findings. An-tenatal transfer to the regional perinatal centre isbeing done for appropriate reasons. Most infants ofvery low birth weight are being born at the level IIIcentre. Among the few infants of very low birthweight born at community hospitals, there is a highrate of neonatal transfer. Finally, for most of theinfants with poor clinical outcomes who were bornat a community hospital either the need for transfercould not have been predicted or the infant couldnot have been transferred.

We also conclude that perinatal care in south-western Ontario became increasingly regionalizedbetween 1982 and 1985. This conclusion is based onthe following findings. The rates of antenatal transferfor early labour, hypertension and failed inductionincreased between 1982 and 1985. The proportion of

CAN MED ASSOC J 1991; 144 (3) 311

births of infants of very low birth weight at com-munity hospitals decreased. There was no substantialshift in place of birth for larger infants, whichindicates that most babies born at or near term werestill being born in the community hospitals. The rateof transfer of neonates of very low birth weight tothe tertiary care centre increased. Finally, neonatesweighing 1500 to 2499 g were less likely to betransferred to the level III centre, which indicateseither increased ability and confidence in caring forsuch babies or decreased risk among infants born atcommunity hospitals or both.

We do not know whether these trends arerepresentative of a general provincial trend towardregionalization of care, are motivated by legal, ethi-cal or other reasons, or are a consequence of theoutreach educational program. Some combination ofthese explanations is likely. The degree to whichregionalization of perinatal care in southwesternOntario is attributable to the educational programcannot be tested since the choice to receive theprogram was made by the receiving hospitals; thus,there is no appropriate "comparison group" notreceiving the program. However, it is reasonable toassume that education played some role in theregionalization of care. Furthermore, the availabilityof an educational program may be a contributingfactor in the decision by smaller level I hospitals tomaintain delivery rooms and continue providingobstetric services. In rural Ontario maintaining levelI obstetric services is essential.

We thank Karen M. Webster, MSc, of St. Joseph's HealthCentre, for her assistance with mathematical modellingand for her interest in this project. We also thank the staffof the community hospitals in southwestern Ontario whocollaborated in this study.

This study was funded by a research grant fromPhysicians' Services Incorporated Foundation. Dr. Camp-bell is funded by Ontario Ministry of Health CareerScientist award 02353. The logistic regression software wasdeveloped for projects for which Dr. Campbell receivedfunding from the Natural Sciences and Engineering Re-search Council of Canada (grant A9244).

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