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By James Chapman
Knackered: Samantha Cameron prepares for the birth of her fourth child Samantha Cameron will not accompany her husband on his historic first trip to the United States as Prime Minister.
Mrs Cameron, 38, is said by friends to be 'knackered' as she prepares for the birth of her fourth child.
Most airlines allow pregnant women to fly up to and including the 36th week, provided the pregnancy has been straightforward.
Mrs Cameron's baby is understood to be due in early September, meaning she could still travel if she wished.
But she pulled out of a trip last month to the G8 and G20 summits in Canada, citing exhaustion, and has apparently baulked at the prospect of another long flight.
She will also miss a trip by the Prime Minister to India to promote a new 'special relationship' with Britain later this month.
'Samantha Cameron was very keen to come to India, but she won't be coming as she is expecting a baby in September,' said one British diplomat.
'The Camerons are very thrilled at the news and don't want to take any chances with the baby on the way.'
The couple tried for another child after the death of their six-year-old son Ivan, who suffered from cerebral palsy and epilepsy, last year.
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