Pippa Middleton, the sister of the
Duchess of Cambridge, has revealed the "happy news" that she is expecting her first child.
The 34-year-old, who is married to hedge fund manager
James Matthews, said she has passed her first trimester and did not suffer from morning sickness.
That contrasts with her sister
Kate, who suffered from Hyperemesis gravidarum - a very severe form of morning sickness - during all three of her pregnancies.
"I was lucky to pass the 12 week scan without suffering from morning sickness," Mrs Middleton wrote in her Waitrose Weekend magazine column. "That meant I was able to carry on as normal".
The fitness columnist, who promises to chronicle her pregnancy workouts for the magazine, is photographed working out and discusses how she has adapted her exercise routine to her condition.
"This being my first pregnancy, I had so many questions I felt were still unanswered," she wrote.
"I wanted to know things like, would I strain if I served in tennis, are all strokes of swimming safe, can I still do a normal yoga class if I avoided certain positions? Could I still work my abs?
"It's particularly hard in the early months when you don't really want to share the news with everyone, not even your class instructor."
After doing some research, she said she adapted her current routine and worked out for 45 minutes, three to four times a week.
She said she had given up jogging because she "liked the idea of giving my body (and growing baby) a rest from pavement pounding."
Instead, when she wasn't in the gym and taking part in classes such as yoga and Pilates, she would walk, cycle, swim and play tennis.
"I've noticed my body change and weight increase, but through effective exercise and sports I feel that it's being strengthened to support a healthy pregnancy, birth and recovery."
She said she avoided "strenuous abs pull-ups" and instead was "conscious of holding my tummy in (as if giving your baby a hug) to support my back and ensure that post-baby, my old favourite jeans will still fit ... eventually."
Speculation over Ms Middleton's pregnancy first emerged in April, days before the birth of the Duke and Duchess' third child, Prince Louis.
Mrs Middleton married Mr Matthews in May last year, with the cream of high society in attendance.