Pippa Middleton has been swimming to keep herself fit throughout her pregnancy. The 34-year-old socialite and author - who is the sister of Duchess Catherine - and her husband James Matthews are set to welcome their first child into the world in just three months' time and, to ensure she's keeping herself nimble ahead of the birth, she's been hitting the pool regularly because it's ''gentle and relaxing.''

Writing for Waitrose's Lifestyle magazine, Pippa said: ''Swimming throughout pregnancy offers a wonderful feeling of weightlessness.

''As the months pass, you feel heavier by the day, but being in water gives that floating, light-as-air feeling that soothes and relieves the body, counteracts increased back strain and stretches the legs from the growing bump.

''It's non-impact, gentle and relaxing. 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.

''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 rounding forwards - a common symptom as your belly expands.

''It can also offset the tendency for your pelvis to be out of alignment. 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 legs.''

Pippa got engaged back in July 2016 and tied the knot with James in May 2017 at St Mark's Church in Englefield, Berkshire, followed by a reception at her family home.