"She is entered into several events, but as with any rider, they treat each event on a case-by-case basis and if she pulls out of an event it will be because the horse isn't ready, rather than her."
But she later warned: "As you can imagine she is following all medical advice from her doctors. She is being sensible about this and is listening to what the doctors are telling her.
"She couldn't be happier about the baby and would never put her pregnancy in jeopardy."
Miss Phillips is well aware of the dangers of riding. She broke her collarbone in 2008 after she came off her horse at an event in France. The animal, Tsunami II, broke its neck and was killed in the fall.
Two years previously her close friend, world-class rider Sherelle Duke, died when her horse fell on top of her during a competition.
The Queen was said to be "delighted" about another addition to her family, as were the parents of Miss Phillips and Tindall.
A spokesman for David Cameron said he would "send his very, very best wishes to the happy couple:".
Later Tindall, a former England rugby captain, joked on Twitter: "Thanks for all the kind messages, we are very excited and I agree with you all that hopefully he/she won't have my nose."
The child will be 16th in line to the throne following the birth of the Duke and Duchess of Cambridge's first baby later this month. It is believed Miss Phillips's mother, Princess Anne, rode until she was 34 weeks pregnant.
- DAILY MAIL