Pippa Middleton revealed that she did not battle severe pregnancy sickness, or Hyperemesis Gravidarum (HG), unlike her sister Kate

Pippa Middleton has confirmed she is expecting her first child with husband James Matthews!

Six weeks after reports first surfaced of her pregnancy, Kate Middleton’s younger sister opened up about her first trimester in her latest column for the U.K. supermarket monthly Waitrose Kitchen magazine.

In the column, the mom-to-be, 34, revealed that she did not battle severe pregnancy sickness, or Hyperemesis Gravidarum (HG), unlike Princess Kate.

“I was lucky to pass the 12-week scan without suffering from morning sickness. That meant I was able to carry on as normal,” Pippa wrote, as reported by Hello! magazine.

In September 2017, Kensington Palace announced that Kate was pregnant with her third child — and noted that she was once again battling HG, similar to when she was carrying Prince George, who turns 5 on July 22, and Princess Charlotte, now 3.

Though Kate was unable to carry out her royal duties during the first months of her pregnancies, sister Pippa was able to continue her everyday schedule, though she admitted she had to make some slight changes.

“When I learned the happy news that I was pregnant, I realized I needed to adjust my four to five-day-a-week [fitness] routine,” she wrote, noting that she kept her pregnancy a secret from her gym instructor until the “riskier months” were over.

Pippa and Kate Middleton
| Credit: LEON NEAL/AFP/GettyImages

Pippa also shared how fitness has been an integral part of her pregnancy.

“I’ve noticed my body change, but through exercise I feel it’s being strengthened,” she wrote. “I’m fanatical about sport and have looked at loads of books and websites on exercise during pregnancy, but have been disappointed by the limited technical information what you can and can’t do.”

So the world’s most famous bridesmaid did her own research.

“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 strokes of swimming safe, can I still do a normal yoga class if I avoided certain positions? Could I still work my abs?”

She added, “I’ve noticed my body change and weight increase, but through effective exercise and sports I feel that it’s been strengthened to support a healthy pregnancy, birth and recovery . . . And ensure that post-baby, my old favorite jeans will still fit eventually!”

The wedding of Prince Harry and Meghan Markle, Pre-Ceremony, Windsor, Berkshire, UK - 19 May 2018
Pippa Middleton and James Matthews
| Credit: James Gourley/Shutterstock

Pippa recently stepped out in London on June 2, and she and Matthews, 41, were also in attendance at the May 19 wedding of Meghan Markle and Prince Harry. Just one day after the royal wedding, the parents-to-be celebrated their one-year wedding anniversary.

Middleton and Matthews tied the knot last year on May 20 at St. Mark’s Church in Englefield. The couple then set off for a whirlwind honeymoon in French Polynesia and Australia.

News of Pippa’s pregnancy came just days before older sister Kate was admitted to St. Mary’s Hospital in London in the early stages of labor with Louis on April 23.

A source previously told PEOPLE that Middleton and Matthews are looking forward to settling down and “having children and leading a quiet life.”