They found a 0.4 per cent prevalence of HIV in a population of 11,593 women from Paris and four suburbs, an area that accounts for 46 per cent of French HIV.
This is higher than a comparable British statistic for inner London, where the highest levels of HIV have been recorded. For inner London prevalence, testing of new-born babies produced an incidence of 0.2 per cent.
The British test shows HIV anti-bodies which the mother has automatically passed to her baby, but it is only conducted following live births. The French test was conducted regardless of whether the women completed their pregnancy and had a live baby.
The research in tomorrow's Lancet says that under half of the HIV women had a live baby - reducing the prevalence rate one and a half times. HIV was also higher in women who had abortions or ectopic pregnancies. They say that for these reasons, neo-natal prevalence studies could also 'strongly underestimate' the prevalence of HIV in pregnant women in France and elsewhere.