The Cochrane Pregnancy andChildbirth DatabaseThe Cochrane CollaborationAnnual subscription £99 (institutional)£57 (individual)Available on 3 5" or 5 25" disk from UpdateSoftware, Oxford OX44 7QB

t is a sign of the times to be asked toreview not a book but a computerdatabase. This is welcome; books are

often out of date even by the time they are

published. The Cochrane Childbirth andPregnancy Database (previously the OxfordDatabase) is a product of secondary research-research that is designed to find andanalyse original research publications. Thatsome secondary research is necessary shouldcome as no surprise, given that mostindividual articles get lost in the mass ofmedical information. The authors of thedatabase have made an immense contri-bution by pulling all of this together, and it isextremely useful both to clinicians and toresearchers, as well as being very easy to use.

The information contained in structuredreviews can provide a clear guide to clinicalaction. While some treatments-such as

administering anti-D immunoglobulinto an Rh negative woman-have obviousadvantages, the effects of other interventions-such as the use of antibiotics at the time ofcaesarean section-cannot be inferred fromsimple clinical observation or deduced fromfirst principles. Individual studies may giveconflicting results because of chance or

inadequate power, and the only way to makesensible use of the world's research effort

is to ascertain all studies, evaluate them forquality, and combine them in a structuredway.The audit committee of the Royal College

of Obstetricians and Gynaecologists hastherefore committed itself to conduct, on athree yearly basis, a careful review of all theevidence in the Cochrane database of trials.This was last done a year ago, and 22clear and auditable clinical recommendationsemerged. This might seem a small harvestfrom such an extensive source-the databasehas 200 reviews and includes data fromnearly 10 000 trials. On the other hand,without it we simply would not have theanswers to many classic questions in mater-nity care. For example, we now know thatroutine induction of labour a week after termis associated with a clear and large reductionin the relative risk of stillbirth. We also knowthat antenatal measures to try to evertthe nipples are of no value whatever inpromoting breast feeding. These are clear cutanswers to longstanding controversies, andthey come from structured reviews updatedin the database over the past two years-hence the value of computer rather thanpaper publication. The database is updatedevery three months.

How the database helps researchersClinical researchers find the database

essential. Knowledge of previous publica-tions is a prerequisite for any research pro-posal. For example, those who are interestedin labour ward management will find that theeffects of routine rupture of the membranesare well documented but that the jury is still

WUk LUI>X .m ' U : - .w

Mitotic spindles in Drosophila, one of the many stunning illustrations in Embryos: Color Atlas ofDevelopment (Wolfe, £49.95, ISBN 0 7234 1740 7), which traces embryogenesis from plants through theslime moulds to animals and humans.

out as far as the effectiveness of oxytocin to"augment" slow labour is concerned. Theseare particularly good examples, because therelevant systematic reviews include datafrom unpublished trials. Experienced re-searchers include evidence from such pre-vious studies in their calculations of samplesize-for example, if meta-analysis of pre-vious high quality studies shows a non-significant worsening of outcome then it ispossible to calculate the number of subjectsrequired to show an improved outcomeacross all studies combined. The value of thedatabase for clinical scientists cannot beoveremphasised.

Relative risksThe current way of presenting results of

clinical trials has two large drawbacks. Thefirst is that these data are typically given asodds ratios rather than relative risk. Whilethese are almost identical when risks are low(a relative risk of 1 in 100 is equivalent toodds of 1 to 99), they are very different whenthe risks are large (a risk of 1 in 6 is equivalentto odds of 1 to 5). Since relative risk is farmore intuitive to clinicians I prefer thismethod of presenting results, and I ampleased that the database includes this option.Even relative risk leaves out a very impor-

tant factor, the absolute risk. For example,giving prophylactic antibiotics halves therelative risk of maternal infection aftercaesarean section irrespective of whether theoperation was done before or during labour.However, the absolute size of this reductionis much greater in intrapartum operationsbecause the baseline risk of infection is muchhigher. The database software deals with thisby giving differences in event rates.

In addition to giving the characteristic 95%confidence intervals (of odds ratios, relativerisks, or differences in event rates) the data-base will also give 99% confidence intervals. Iwould like to have 80% confidence intervalsas well, because some unbiased evidence isbetter than none at all, and it is not necessaryto be 97-50/o confident that one treatment isbetter than another in order to select it-it ismerely necessary to perceive a greater likeli-hood of benefit.The statistical technique to combine the

results of trials by meta-analysis in this (andall other current databases) is the Mantel-Haenszel statistic. This seems an inappro-priate statistical method because it assumesthat all trials come from a hypothetical andinfinitely large body of trials-that there isone underlying true effect. Clearly this is notso (clinical outcomes differ according topopulations and the characteristics ofclinicians, in different places and over time)and I would therefore prefer statistical tech-niques that do not rely on this underlyingassumption. Nevertheless, this is a criticismof current worldwide practice rather than ofthis specific database.-RICHARD J LILFORD,professor of obstetrics and gynaecology, University ofLeeds

BMJ VOLUME 308 28 MAY 1994

nk.,'Vb Ipi ------ - ---

WMIIIORVIIVZOW,...

1 448

I l*:ssl

Best books on obstetrics: a personal choice

For students*** Essential Obstetrics and Gynaecology. E MSymonds. (£20.99.) Churchill Livingstone, 1992.ISBN 0-443-02207-0.** Obstetrics by Ten Teachers. 15th edn. T Lewis,G Chamberlain. (£ 15.99.) Edward Arnold, 1990.ISBN 0-340-515650-X.** Fundamentals of Obstetrics and Gynaecology.D Llewellyn Jones. (£15.00.) Faber, 1990. ISBN0-571-142273.**** Illustrated Textbook of Obstetrics. G Cham-berlain, C Gibbons, J Dewhurst. (£16.95.) Gower,1989. ISBN 0-397-44580-6.* Lecture Notes on Obstetrics. 6th edn. G Chamber-lain, MJ Pearce. (12.95.) Blackwell Scientific, 1992.ISBN 0-632-02771-1.* Student Notes on Obstetrics and Gynaecology. JWillox, J Neilson. (_ 11.50.) Churchill Livingstone,1990. ISBN 0-443-041504.

or undergraduate students there is noideal book on obstetrics. Some of thesmaller books-for example, Lecture

Notes on Obstetrics, Student Notes on Obstetricsand Gynaecology-tend to issue brief lists offacts. In many medical schools the amount oftime allocated to obstetrics and gynaecologytogether is often only a few weeks, andcurrently the amount of core knowledge thatstudents have to assimilate is considerable.The emphasis for undergraduates studyingobstetrics, and thus all potential medicalpractitioners, should be geared towards thenormal rather than the abnormal, thereforeincluding physiological adaptations to preg-nancy, fetal growth and wellbeing, andnormal labour and delivery. The recognitionof the abnormal is important, but textbooksshould concentrate on those problems whichare commonly found in clinical practice.Although students vary in their methods

of learning, active participative learning isadvisable rather than rote learning withregurgitation of lists of facts in order to passexaminations. My preferences for under-graduates are books that concentrate onfundamental aspects of normal pregnancyand delivery. I would specially recommendtwo books-namely, the Illustrated Textbookof Obstetrics and Essential Obstetrics andGynaecology. The latter has an advantage inthat obstetrics and gynaecology are containedtogether in one volume at a fairly modestprice that undergraduates can afford.

For general practitioners** Modern Obstetrics and General Practice. Ed J NMarsh. (£;20.) Oxford University Press, 1985. ISBN0-19-2614-193.*** Pregnancy Care in the 1990s. Ed G Chamberlain,LZander. (£18.95.) Parthenon, 1992. ISBN 1-85070-393-0.

T| ahere are not many books aimedspecifically at general practitioners.The exception is the first one listed

above. Its target readership is general prac-titioners beginning to do obstetrics. The

From A-M Le Boursier du Coudray's "Traiti desAccouchements, " 1759.

book therefore considers mainly antenataland postnatal care, although there is a sectionon intrapartum care and the part playedtherein by general practitioners. It bringstogether views about general practitionerobstetric practice from women, specialists,midwives, general practitioners, statisticians,and sociologists and provides an excellentbasis for general practitioners aiming to takethe DRCOG examination. Pregnancy Carein the 1990s draws together issues centralto the development of the care of womenin pregnancy in the 1 990s and examinescritically the responsibilities of differentprofessionals and society. It should be readby all those providing and using services,the women having babies, consumer groups,midwives, general practitioners, obstetri-cians, paediatricians, managers, and politi-cians.

For specialists*** Obstetrics. Ed A T Turnbull, G Chamberlain.(£130.) Churchill Livingstone, 1989. ISBN 0-443-03539-3.*** Scientific Foundations of Obstetrics andGynaecology. Ed E Philipp, J Barnes, M Newton.(£;125.) Butterworth-Heinemann, 1991. ISBN0-433-251034.S Bailliere's International Practice and Research:Clinical Obstetrics and Gynaecology. Subscription£72, single issues 27.50. ISBN 0950-355-2.** Progress in Obstetrics and Gynaecology. Vol 10.Ed J Studd. (£26.50.) Churchill Livingstone, 1993.ISBN 0443-04754-5.** Recent Advances in Obstetrics and Gynaecology.Vols 16 and 17. Ed J Bonnar. (,£22.50.) ChurchillIivingstone, 1993. ISBN 0-443-04402-3.

rainee specialist obstetricians aiming* for the MRCOG need to develop avgreater depth of knowledge and

understanding of the subject. ScientificFoundations aims at giving readers an enor-mous range and depth of information fromexperts in all the basic science and clinical

research that would be appropriate for themodern specialist, and a good understandingof the principles outlined in this book isnecessary for those in training. Obstetrics,with a short section on basic sciences andconcentrating on care in pregnancy bothnormal and abnormal, aims at providing acomprehensive account of the knowledgeand practice of this specialty needed byyoung obstetricians in training for the 1 990s.It is a multiple author volume, and occasion-ally this leads to overlap between the sections.Some sections have many references, othershave relatively few. Nevertheless, this bookprovides an excellent basis for traineespecialists. A second edition is planned andsome of the deficiencies of the first editionmay therefore be corrected. The book wouldalso serve as an excellent reference for anyhealth professional with a query about ob-stetric practice.

Large books such as those just discussed,however, are often slightly out of date by thetime they are published, and both traineesand established specialists need to keep up todate. The last three volumes listed above areall excellent in this respect. Bailli&re's ClinicalObstetrics and Gynaecology provides up to themoment overall reviews and current opinionin obstetrics and gynaecology. It is compre-hensively referenced and illustrated andis written and edited by internationallyrenowned experts. Alternatives, Progressin Obstetrics and Gynaecology and RecentAdvances in Obstetrics and Gynaecology, arealso excellent value for money. These lattertwo tend to cover smaller subsections oftopics and to be written by experts whereasBailliere's Clinical Obstetrics and Gynaecologyconcentrates on broader topics with compre-hensive coverage ofthem.

Additionally, all obstetric and midwiferypractitioners should be able to obtain readilyinformation about the effects of care forresearch and audit purposes. The CochraneCollaboration's Pregnancy and ChildbirthDatabase, 1993 gives easy access to reliableand regularly updated systematic reviewsand outcomes of clinical trials.For subspecialists or obstetricians with a

special interest in one aspect there is a widerange of books available. Specialists in ultra-sonic scanning have a large number, manybeautifully illustrated, from which to choose.There are books relating to aspects offetal medicine, multiple pregnancy, pre-eclampsia, diabetes, and preterm labourfrom which obstetricians with a specialinterest may select. Generally these providea comprehensive account of the topicunder review, are well referenced, andcould be used by obstetricians beginninga specific interest or indeed by those moreexpert in the subject.-DoRIS CAMPBELL, seniorlecturer in obstetrics and gynaecology, University ofAberdeen

BMJ VOLUME 308 28 MAY 1994 1449