Photos of the Duchess of Cambridge's visit to a London maternity unit in November were released Friday along with an open letter addressed to midwives in which she praised their "amazing work" of improving "the lives of others."

The photographs show the duchess meeting with staff and checking in on a couple's baby.

Catherine, the wife of Prince William, spent two days at Kingston Hospital Maternity Unit in southwest London, according to a November 27 Court Circular, which is the official record of royal engagements.

The duchess explained in the letter that she accompanied community midwives during the visit, where she was welcomed into people's homes, and spent time in post-natal wards and hospital clinics.

"I was truly touched by the trust that people placed in me, sharing their experiences and voicing their fears openly," she wrote.

"No matter the setting, I was continually struck by the compassion that those of you I spent time with showed, and the incredible work ethic you demonstrated on behalf of your entire profession — not only performing your rounds but working tirelessly through the night to support people that were at their most vulnerable."

The visit was part of Catherine's focus on "Early Years," which she explains in the letter as being the "pivotal period of development between pregnancy and the age of 5 where children build crucial foundations for life."

"Even before we are born, our mother's emotional and physical health directly influences our development and by the age of 5 a child's brain has developed to 90% of its adult size," she wrote, adding that midwives' role at "the very start of this period is therefore of fundamental importance."

According to the website of the Royal Foundation, the principal charitable vehicle for the Duke and Duchess of Cambridge, Catherine aims to "develop a significant new body of work that will ultimately support all efforts to provide children with the best possible start in life" via her Early Years project.