SummaryWe aimed to assess the sensitivity and predictive values of usingKnox scoring in the United Kingdom, in order to reduce unnec-essary hospital referral. One hundred and sixty-six pregnantwomen were assessed at booking by the current antenatalscoring as well as by Knox scoring and then the same womenwere reassessed at 36 weeks’ gestation. At booking Knox scored11·7% of women as high risk while the current antenatal systemscored 48·9%. At 36 weeks’ gestation Knox scored 1·4% of thesame pregnant women as high-risk when our scoring systemidenti� ed 37·9% as high-risk women. We had one case of peri-natal death and nine cases of perinatal morbidity. Knox scoringshowed a higher positive predictive value (17·6% vs. 12·1%)but less sensitivity (30% vs. 90%) than the current scoringsystem. That will lead to dramatic reduction of hospital refer-ral at the booking visit from 48·9% to 11·7% and late in preg-nancy from 37·9% to 1·4%.

IntroductionIdenti� cation of pregnancies that are at greater thanaverage risk is a fundamental component of antenatalcare (Enkin et al., 1998). The identi� cation of high- andlow-risk pregnancies is potentially bene� cial to both the patient and the health system (Lesinski, 1975;Webster et al., 1988). Current obstetric risk-scoringsystems depend upon simple addition of weighted andunweighted risk factors (Chard et al., 1990, 1992).Several authors have proposed systems for calculatingthese scores, most of them targeted toward the predictionof premature labour (Creasy et al., 1980; Herron et al.,1982; Ross et al., 1986; Main et al., 1987; Mueller-Heubach and Guzick, 1987).

The informal (clinical) antenatal risk assessment wasclassi� ed by Hobel et al. as level 1 obstetric risk assess-ment. Level 2 uses the presence or absence of single riskfactors to decide whether a person is at risk (the currentsystem in the United Kingdom). In this level, a largenumber of women will be considered high risk and allrisk factors are considered to have an equal effect onoutcome. The third level assigns each factor a statisticalweighting to re� ect the fact that different risk factors havediffering levels of effect (Hobel et al., 1973). The use ofstatistical weighting is potentially more effective thanclinical weighting because it excludes experiential bias.

Knox et al., developed a statistically weighted riskscoring system from the National Women’s Hospital,New Zealand using 27 signi� cant antenatal variables(Knox et al., 1993). We, therefore, performed a prospec-

tive study to compare antenatal risk status as determinedby the Knox scoring system (level 3) with our currentrisk scoring system (level 2). The main objective was toassess the sensitivity and predictive values of using Knoxscoring in the British community, in order to assign cor-rectly the level of antenatal care needed and to reduce theunnecessary hospital referral.

Materials and methodsOne hundred and sixty-six pregnant women wereassessed at the booking clinic at Basildon Hospital, usingthe current antenatal scoring system as well as the Knoxscoring system. The same women were reassessed at 36weeks of gestation by both systems. Our current antena-tal scoring system includes 50 risk factors with a scoreof 1 or 0 for each variable present or absent (level 2).These factors cover personal, medical, surgical, socialand family history as well as previous obstetric hospital.High-risk pregnancy was allocated when the added scorewas over four.

The Knox scoring system contains 27 risk factors, cov-ering the same aspects as our current scoring but with sta-tistical weighting. The high-risk pregnancy was identi� edusing the exact sum of logistic coef� cients used by theKnox score (>0·4 at booking and >2·75 at 36 weeks). Thedata sheets were analysed in respect of agreement and dis-crepancy of the two scoring systems for predicting theobstetric (perinatal) outcome. A poor outcome was de� nedas perinatal death (any death after 20 weeks of pregnancyor in the � rst week of life) or perinatal morbidity (de� nedas a stay of longer than 5 days in a neonatal unit).

ResultsAntenatal forms were completed correctly for 145 preg-nant women at the booking and 36 weeks’ gestation visits.The Knox scoring system identi� ed 17 pregnant women(11·7%) as high risk and 128 (88·3%) as low risk at thebooking visit. Our current antenatal scoring systemscored 71 women as high risk pregnancy (48·9%) and 74(51%) pregnant women as low risk.

At 36 weeks of gestation, the Knox scoring systemallocated only two (1·4%) women as high risk pregnancyand 143 (98·6%) as low risk, while our current systemscored 55 (38%) pregnant women as a high risk and 90women (62%) as low risk pregnancy.

OBSTETRICS

Can the New Zealand antenatal scoring systembe applied in the United Kingdom?

H. MOHAMED, C. MARTIN and R. HALOOBDepartment of Obstetrics and Gynaecology, Basildon Hospital, Essex, UK

Journal of Obstetrics and Gynaecology (2002) Vol. 22, No. 4, 389± 391

Correspondence to: R. Haloob, Department of Obstetrics and Gynaecology, Basildon Hospital, Essex, UK.

ISSN 0144-3615 print/ISSN 1364-6893 online/02/040389-03 � Taylor & Francis Limited, 2002 DOI: 10.1080/01443610220141335

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Both scoring systems agreed in identifying high-riskwomen at booking in only 24% (17/71) of cases, but this agreement decreased signi� cantly to 3·6% (2/55) at36 weeks of gestation. Conversely, the agreement wasincreased from 58% (74/128) at booking to 63% (90/143)at 36 weeks’ gestation in identifying low-risk pregnantwomen.

Ninety-six pregnant women (66·2%) of the studygroup had normal vaginal deliveries, 21 (14·5%) deliv-ered by vacuum extraction, and seven women (4·8%)delivered by forceps. Emergency caesarean sections wereperformed in nine women (6·2%) and 12 patients (8·3%)opted for elective caesarean section. The two women whohad been assigned as high-risk pregnancy by the Knoxscoring system at 36 weeks’ gestation had vaginal deliv-ery. No major maternal morbidity was reported from thestudy group.

Ten pregnant women (6·8%) had a poor perinataloutcome during the study period: one case of perinataldeath at 25 weeks’ gestation following vaginal deliveryand nine cases of perinatal morbidity (>5 days admissionto neonatal unit). Three of these cases had been predictedby the Knox scoring system with a positive predictivevalues of 17·6% (Table I), while our current scoringsystem predicted nine of the 10 cases with a positive predictive value of 12·1% (Table II).

DiscussionIn this study we have attempted to apply a new statisti-cally weighted scoring system during the antenatal periodand comparing it with our current system with a view toreducing unnecessary hospital referral without compro-mising the antenatal care. We gave every pregnant womanin the study group two scores, with no change of thenumber of hospital visits or the plan of care from ourstandard care. The perinatal outcome was selected as theprimary outcome measures, as it is a readily identi� ableindicator of poor outcome, but other measures could havebeen used, such as caesarean delivery, low birth weightand poor Apgar scores (Morrison et al., 1980).

The number of women assigned as high-risk pregnancywas reduced dramatically by the Knox scoring system in both booking and late pregnancy visits, with a higher

positive predictive value than our current scoring sytem.Knox et al., reported a positive predictive value of 16%that is nearly similar to our results (18%) and higher thanour current scoring system (12%). We demonstrated thatthe current scoring system has a higher sensitivity (90%)than Knox scoring (30%), and both � gures are differentfrom those reported by Knox et al. (72%). This could beexplained, as it is probable that the predictive accuracyof any score is altered by the frequency of poor outcomein the population tested.

Despite the differences in the sensitivity, speci� cityand positive predictive values between both systems, theyagreed in identifying the low-risk women in more than half of women in the study group. The available datafrom the literature demonstrate no signi� cant differencesin perinatal outcomes for low-risk women receiving care at midwifery/general practitioner-managed careversus obstetrician/gynaecologist-led shared care (Khan-Neelofur et al., 1998).

The health economic evaluation of the two scoringsystems was not considered in this study, as we did notchange the number of antenatal visits through the studyperiod, but reduction of the number of women referredto hospital will de� nitely result in reduction of costs.

We can conclude that despite the agreement of bothscoring systems in predicting the low-risk pregnantwomen, they signi� cantly fail to agree in predicting high-risk pregnancy. The Knox scoring system resulted in ahigher predictive value than the current scoring systemused in the United Kingdom. This may lead to a dramaticdecrease of hospital referral at both booking and late inpregnancy visits, with subsequent health economic impli-cations. A consideration is required to apply the NewZealand Knox antenatal scoring system in Britain onlyafter a larger number in a randomised study.

ReferencesChard T., Harding S., Carroll S., Hudson C.N., Lloyd D.S. and

Sloan D. (1990) A comparison of different methods for calculating overall risk scores from risk factors ascertainedin a computerised obstetric information system. Journal ofPerinatal Medicine, 18, 23–29.

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Herron M.A., Katz M. and Creasy R.K. (1982) Evaluation of preterm birth prevention program: preliminary report.Obstetrics and Gynecology, 59, 452–456.

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390 H. Mohamed et al.

Table I. Perinatal outcome in Knox scoring

Poor outcome Good outcome Total

High risk 3 14 17Low risk 7 121 128Total 10 135 145

Sensitivity: 30% (3/10); speci® city: 90% (121/135); positivepredictive value: 17´6% (3/17).

Table II. Perinatal outcome in current scoring

Poor outcome Good outcome Total

High risk 9 62 71Low risk 1 73 74Total 10 135 145

Sensitivity: 90% (9/10); speci® city: 54% (73/135); positive pre-dictive value: 12´1% (9/71).

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Knox scoring in the UK 391

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