Angela Cannings was jailed in April 2002

Cannings, 40, from Salisbury in Wiltshire, was convicted last year of smothering seven-week-old Jason in 1991 and 18-week-old Matthew in 1999.

She has always maintained they were victims of sudden infant death syndrome (SIDS) or cot death.

On Monday, Lord Justice Judge, Mrs Justice Rafferty and Mr Justice Pitchers heard that Mrs Cannings' relatives had also lost babies.

On Friday the court had heard that Jason and Matthew had each suffered an "acute life-threatening event" (ALTE) in the week prior to their deaths.

Recent research suggests that the incidence of SIDS is 10 to 15 times more likely after an ALTE and that the recurrence rate of SIDS after a prior cot death was almost six times greater than in a "normal" family.

'Unexplained circumstances'

On Monday, Cannings' counsel Michael Mansfield QC called for evidence from consultant clinical geneticist Professor Michael Patton.

Prof Patton told the court that new information gathered by the BBC's Real Story programme from a genealogist in Ireland showed that the great-grandmother and grandmother of Angela Cannings also lost babies in unexplained circumstances.

The programme's research also found evidence of an unexplained ALTE in another branch of the family.

Prof Patton agreed under cross-examination that he could not diagnose the causes of death and that factors other than a genetic link could have been involved.

The hearing was adjourned until Tuesday.