Just under 50% of women are waiting until they reach 30 to give birth, according to the latest figures from the Office for National Statistics.
In 2010, 48% of all infants born were to mothers aged 30 and over, up from 47% in 2009 and 46% in 2000.
The last time so many babies were born to women of this age was after the Second World War, in 1946.
The proportion of mothers under the age of 25 has fallen steadily since its peak in the early Seventies.
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Detectives in Westminster are investigating after the man was discovered on the Route 189 bus in Marylebone shortly after midnight.
The murderer was shaking and appeared to be gasping for air for around 13 minutes before dying.