A drop in the rate of children being adopted is partly caused by improvements in IVF, the head of the public body representing children in care said.
The success rates for fertility treatment are now nearly three in 10 (29%) for women under 35, almost three times higher than when the process was first developed in 1978.
Anthony Douglas, the chief executive of the Children and Family Court Advisory and Support Service (Cafcass), also told the Daily Telegraph the adoption process was “far too slow”.
He said: “IVF used to be around 7% successful and now it’s around 30%.
“So as a choice, adoption is competing with lots of other ways of having children.”
While the number of children in care has increased in England – the figure stood at 72,670 as of March 31 2017 – the number of adoptions has fallen in recent years to 4,350 in 2017, down from 5,360 in 2015.
Mr Douglas, who will step down from his role in March, also said the wait for children to find their “forever home” needed to be cut.
He told the paper: “Every child deserves a family to live and grow up in but adoption still takes twice as long as it should, which puts people off.”
Figures from the Department of Education say that in England the average duration between entry into care and being adopted has fallen from 30 months to 24 months in 2017 owing to improvements in the early stages of the process.