The Office for National Statistics tracks the average number of daily births for each date using figures over two decades.
This method reveals April 28 as the date for the period the former Suits actress has mentioned - with 1,833 births.
April 30 and 26 both have 1,815 births, and are also contenders.
Husband Prince Harry attended two engagements today including the twelfth annual Lord Mayor’s Big Curry Lunch and the premiere of Our Planet with his father Prince Charles and brother Prince William.
The heavily pregnant Duchess of Sussex was not in attendance as she's started her maternity leave from royal engagements.
Watch William and Harry join Charles for a rare joint engagement at Our Planet premiere: