Zara, who is married to rugby player Mike Tindall, will hang up her riding boots for the rest of the year but will return to the sport once their baby has arrived.
The Queen's granddaughter, who is three months pregnant, was pictured playing polo on Sunday and was snapped competing at the Brightling International Horse Trials in East Sussex on 14 June.
But although Zara loves the sport, she wants to be "sensible" while she is expecting.
In a statement, Zara's spokesperson said: "The fact is that all of Zara's horses have now qualified for the events she wishes to enter them for next year.
"She has done so well already this season, she does not actually need to compete any more. Given that she is pregnant, she has decided to cancel the rest of her entries for the year.
"She is feeling fine and is following all medical advice from her doctors. She is just being sensible about this. If there is no reason for her to ride, then she won't."
Last year, Zara and her fellow GB Equestrian teammates won a silver medal for show jumping at the London 2012 Olympics.
The daughter of Princess Anne and England rugby champ Mike revealed last week that they are expecting their first baby together.
The couple married at Canongate Kirk, in Edinburgh, in July 2011.
See who else is expecting in our gallery below!
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