Murder should never be ruled out when investigating repeat cot deaths, in spite of claims that most are natural, a study suggests.

Several high-profile cases have focused attention on couples who suffer more than one cot death. The view that a second, or a third, cot death in the same family should be taken as evidence of homicide has been discredited after court verdicts in these cases.

But has the pendulum now swung too far? In British Medical Journal, two senior (and now retired) paediatricians from Yorkshire, Christopher Bacon and Edmund Hey, review the evidence, focusing on a study published in The Lancet two years ago that suggested almost 90 per cent of repeat cot deaths were natural. The study has been influential in swinging opinion away from the view expressed by the paediatrician Professor Sir Roy Meadow that two cot deaths was highly suspicious, and three almost certain evidence of homicide.

Sir Roy’s disputed evidence in the case of Sally Clark, who was convicted of killing her children before being cleared on appeal, led to his being struck off by the General Medical Council – a decision also later reversed, by the High Court.

The original Lancet study looked at 46 repeat cot deaths, classifying 40 of them as natural and just six of them as unnatural – that is, murder or manslaughter. But this is a misleading way of looking at it, say the two paediatricians. They review the original data and reclassify cases into three categories: probably natural, probably unnatural and undetermined. The six homicides constitute the probably unnatural group, while the other 40 cases divide equally between probably natural and undetermined. According to this classification, 43 per cent of the deaths are undetermined and may be the result of violence from parents or others. This fits more closely, say the authors, with earlier studies that suggested about 40 per cent of repeat cot deaths were homicides.

“We think using a dichotomy of natural or unnatural is unhelpful,” they say. “It glosses over complexities and uncertainties and fosters polarisation.

“Uncertainty may be uncomfortable, but it is truer to reality, more conducive to scientific inquiry and safer for children than a dogmatic stance at either pole. Experience in child protection teaches that it is often impossible to determine whether the parents have been in some way and to some degree responsible for the unexplained death of their baby.”

They said the The Lancet paper could possibly “lead to mistakes in child protection”, adding: “We would encourage professionals to keep an open mind in assessing unexplained infant deaths, to be aware of the difficulties in diagnosis and to try to keep a balance between supporting parents and the need to protect children.”

Sally Clark was convicted of murdering her two sons but freed by the Court of Appeal in 2003.

The evidence that helped to convict her included a claim made by Sir Roy Meadow at her trial that there was a “one in 73 million” chance of two children dying from cot death in the same affluent family.

He later acknowledged that his use of the statistics had been “insensitive”. Two other women at whose trials he had given evidence were also freed.

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