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Ritodrine in the Treatment of Preterm Labour. A Clinical Trial to Compare a Standard Treatment with Three Regimens Involving the Use of Ritodrine

Sir, As statistician responsible for the data analysis, I have strong reservations about the paper by Larsen etaZ(1980). The authors fail to mention that the relatively small pretreatment incidence of Bishop scores of 6 or more (10 or more in the units of the paper) in the standard treatment group (17 per cent) as compared with the combined ritodrine groups (40 per cent) represents a statistically significant (p = 0.037) imbalance. The absence from the standard treatment group of fetuses with congenital malformations, in the face of 12 such fetuses in the ritodrine treatment group, is further evidence of a bias in the treatment allocation, invalidating the study. The authors seem to recognize this as they speak in paragraph 5 of their Discussion of a new trial which they presumably hope will not suffer such biasses. The paper also presents ample evidence that many patients in the standard treatment group were not in need of treatment with tocolytic drugs: their mean gestational age at delivery was 36 weeks and 4 days and 67 per cent of the patients gained two or more weeks gestation after the first episode of preterm labour. For the establishment of the efficacy of a drug, a population is needed that can benefit from the drug. The results of the standard treatment were so good that no active drug could have effected much improvement. I must, therefore, conclude that the wrong patient population was studied. This conclusion was supported by the fact that in the group of patients with high pretreatment Bishop scores, my analysis showed markedly better results with ritodrine than with standard treatment (Table I). Unfortunately, as already stated, there were statistically significantly fewer patients with high Bishop scores in the standard treatment group than in the ritodrine groups and no sensitive statistical comparison was possible.