Image copyright Kensington Palace/PA Media Image caption The Duchess of Cambridge visited a maternity ward in London last month

The Duchess of Cambridge has commended the UK's midwives for their "amazing work bringing new life into our world" in an open letter to those in the profession.

In the letter, Catherine says: "You are there for women at their most vulnerable; you witness strength, pain and unimaginable joy on a daily basis."

It comes after the duchess spent two days shadowing healthcare workers at a maternity unit in London in November.

She also praised the staff's kindness.

In the letter, the duchess told midwives: "Your work often goes on behind the scenes, and away from the spotlight.

"Recently however, I was privileged enough to witness a small section of it first hand, spending several days at Kingston Hospital's maternity unit.

"Although this was not my first encounter with the care and kindness provided by midwives across the country, it gave me a broader insight into the true impact you have on everybody you help."

Image copyright Kensington Palace/PA Media Image caption Catherine spent time with staff at Kingston Hospital's maternity unit

The letter was published ahead of the World Health Organization's international Year of the Nurse and Midwife in 2020, which will celebrate the work of nurses and midwives and highlight "the challenging conditions they often face".

Kensington Palace also released four pictures of her time on the maternity unit.

Image copyright Kensington Palace/PA Media Image caption The Duchess of Cambridge took part in home visits during her time on the unit

She told the midwives: "The help and reassurance you provide for parents-to-be and parents of newborns is just as crucial.

"It goes a long way in building parents' confidence from the start, with lifelong impact on the future happiness of their children.

Catherine has advocated the improvement of early years support for children and their parents, believing it can help mitigate "many of society's greatest social and health challenges".

The duchess has three children under the age of seven - six-year-old Prince George, four-year-old Princess Charlotte, and 20-month-old Prince Louis.

Image copyright AFP Image caption The Duchess of Cambridge gave birth to her third child, Prince Louis, in April 2018

As part of her work at her and her husband's charity, the Royal Foundation, the duchess brought together a group of academics, practitioners and charities last year to look at how to provide children with the best start in life.

The foundation's website says the steering group plans to produce "significant new body of work".

Catherine's letter, to be posted on the Royal College of Midwives' website, goes on to say: "The founder of modern nursing, Florence Nightingale - whose 200th anniversary we celebrate next year - once said, 'I attribute my success to this: I never have or took an excuse' and it is that mantra that I have seen time and time again in all of my encounters with you.

"You don't ask for praise or for recognition but instead unwaveringly continue your amazing work bringing new life into our world.

"You continue to demonstrate that despite your technical mastery and the advancement of modern medicine, it is the human to human relationships and simple acts of kindness that sometimes mean the most."

Image copyright Kensington Palace/PA Media

Professor Jacqueline Dunkley-Bent, England's chief midwifery officer, who helped deliver Catherine's children, said: "Around 650,000 babies were born this year with our fantastic NHS midwives on hand to provide care to women and their families.

"It is a huge honour for the duchess to recognise the importance of our profession and, as we look ahead to 2020, her support will no doubt be a massive boost for all those working in maternity services as we celebrate the year of the nurse and the midwife."