A second study, also published today, shows some improvement in the number of extremely preterm children who survived without disability at 3 years of age, but no change in the rate of serious health and developmental problems over the same 10-year period.

Taken together, these two large studies (known as the EPICure studies) suggest little progress has been made in reducing serious long term problems in extremely premature babies, despite the introduction of a range of measures designed to improve clinical outcomes.

Extremely preterm birth (before 26 weeks of gestation) is associated with high rates of death and, for those who survive, a range of problems requiring additional help from health, education, and social services and with lifelong implications. Rates of preterm birth are rising in many European countries and are particularly high in the UK.

Previous studies suggest that deaths have fallen in babies born before 26 weeks, but there is no evidence for those born at the extremes of prematurity (22 to 25 weeks).

The first study reports survival and outcomes until initial discharge from hospital for babies born in 2006 at 22-26 weeks' gestation and compared outcome for babies born at 22-25 weeks in 1995 and 2006. Serious conditions included lung disease, brain injury and retinopathy (a disease that can lead to loss of vision).

Between 1995 and 2006, the number of admissions to neonatal intensive care units of babies born at 22-25 weeks increased by 44%, from 666 in 1995 to 1,115 in 2006.

By 2006, survival shortly after birth increased by 13% (from 40% to 53%), but the proportion of survivors leaving hospital with major health problems was unchanged.

Despite the introduction of a range of evidence based interventions associated with improved outcomes, there was little evidence in 2006 that serious conditions have altered over the intervening 10 years, say the authors.

These results suggest that the total number of children in the community with lifelong health problems as a result of extremely preterm birth will rise, and represents an important increase in workload for health, educational, and social services, they conclude.

The second study compared neurological and developmental outcomes at age 3 years in babies born before 27 weeks in 2006 with babies born between 22 and 25 weeks in 1995.

For preterm babies born in 2006, severe disability at age 3 years increased as gestation shortened, from 20% of survivors at 26 weeks' gestation to 45% at 23 weeks. The most common impairment was developmental or cognitive function.

After taking account of missing data, the results show that between 1995 and 2006, the proportion of survivors with severe disability at 3 years was unchanged. However, an estimated 11% more babies born between 22 and 25 weeks survived without disability.

In this second study, there is some evidence of improvement in the proportion of babies who survive without disability, but no change in the rate of severe impairment, say the authors.

However, they stress that these findings should be interpreted with caution, and say "only assessment of the 2006 cohort at school age will clarify whether there have been important changes in the high prevalence of impaired cognitive and behavioural outcomes."