Kate Middleton, Pippa Middleton
Pippa Middleton and James Middleton attend day four of the Wimbledon Lawn Tennis Championships at All England Lawn Tennis and Croquet Club on July 5, 2018 in London, England.Getty Images

Kate Middleton's sister Pippa Middleton is expecting her first child with husband James Matthews. While she's already giving us maternity fashion goals, the British royal family member's sister reveals how she has been using swimming to keep herself fit during her pregnancy.

In her latest columns for the UK supermarket monthly Waitrose Kitchen, she revealed that she has been diving into her third trimester one stroke at a time.

"From personal experience, I'd confidently say I find it has been the most enjoyable and rewarding form of exercise since I found out I was expecting. It's comforting to know that it's safe throughout pregnancy, and you don't need to adapt and change too much (unlike most other sports). It's so good for you that you could swim every day – as long as you don't overexert yourself – right up until the end of the third trimester," she wrote.

The 34-year-old added that swimming "offers a wonderful feeling of weightlessness" while helping as a form of a good workout.

"As with other forms of exercise, it boosts oxygen levels and strengthens the heart, enabling you to get more nutrients to your unborn child to help them grow. It's also one of the most therapeutic ways to work out, particularly when you become less mobile, and it helps prevent your shoulders from rounding forwards – a common symptom as your belly expands. It can also offset the tendency for your pelvis to be out of alignment," she said.

Pippa Middleton and James Matthews
Pippa Middleton and James Matthews arrive at the wedding of Prince Harry to Ms Meghan Markle at St George's Chapel, Windsor Castle on May 19, 2018 in Windsor, England.Chris Jackson/Pool via REUTERS

She details other benefits of swimming during pregnancy. "As the summer weather contributes to feelings of bloating and swelling, swimming will keep your body cooler while exercising, something that is a relief in pregnancy, preventing swelling in the arms and leg," she wrote.

But even in the cooler months, temporarily joining a local pool can be worth the investment. If this is the only exercise you do during pregnancy, you're onto a good thing!"

Pippa announced her pregnancy through her column after rumours went wild suggesting that she was gearing up to welcome her firstborn. The Middleton sister hasn't revealed when she's expecting the baby to arrive.