The conception rate among under-18s in England and Wales fell 1.4% between 2003 and 2004, official figures show.
Fewer teenagers are becoming pregnant
But although under-18 conceptions have now fallen by 11% since 1998, the government has missed its target of a 15% fall by 2004.
In contrast, the conception rate among women aged 40-44 jumped by 6%.
Data from the Office for National Statistics show the overall conception rate rose by 2% from 73.7 to 75.2 conceptions per 1,000 women aged 15-44.
The figures also show average life expectancy in Britain rose by 5.1 years to 76 for men, and 3.7 years to 80.5 for women between 1981 and 2002.
However, on average just under half of the added years were spent in disability.
In total, there were an estimated 826,000 conceptions in England and Wales in 2004, compared with 807,000 in 2003 - an increase of 2.4%.
Nearly 80% of these conceptions resulted in a live birth.
The figures show:
- The conception rate among women aged 40-44 increased from 10.7 to 11.3 conceptions per 1,000 women between 2003 and 2004.
- The conception rate for girls aged 13-15 was 7.5 per 1,000 in 2004, compared with 8.0 per 1,000 in 2003 - a fall of 6%.
- The conception rate for teenagers aged 15-17 was 41.7 per 1,000, compared with 42.3 in 2003.
The figures also show that in the UK in 2002, on average males could expect to live 67.1 years in good or fairly good health, and another 8.8 years in less robust health.
For females, the figures were 69.9 years in good health, and 10.6 years in ill health.
Teenage figures welcomed
Beverley Hughes Minister for Children, Young People and Families said the figures showed the government was making steady progress in cutting teenage pregnancies.
"By international standards, the UK has had high rates of teenage pregnancy for 40 years.
"Today's figures show that the government's continued focus on this issue is having a positive effect with the rate of teenage conceptions now at the lowest point since the mid-1980s."
She said particular progress had been made in deprived areas, where teenage conceptions are high, but admitted some areas lagged behind.
"To accelerate progress towards our target of halving teenage pregnancies by 2010, we will need to ensure that all local authorities are delivering at the level of the best."
Toni Belfield, of the Family Planning Association, said conceptions in the under-16s had fallen 15.2% since 1998.
"Teenage pregnancy is a complex social issue for which there is no quick fix and continued progress in reducing rates requires an ongoing commitment from government.
"The current strategy, which involves a combined approach from health, education and social services, along with the involvement of parents and young people, remains a sound basis for progress."
Jan Barlow, of the sexual health charity Brook, said further progress was dependent on young people being given access to confidential medical advice, and comprehensive education on sex and relationships at school.