Britain's Catherine, Duchess of Cambridge
Britain's Catherine, Duchess of Cambridge speaks with museum director Michael Dixon as they leave the Natural History Museum in London October 21, 2014. Reuters

Kate Middleton's return to public appearances after her bout of Hyperemesis Gravidarum was marked with "sexy style choices" for her maternity wardrobe. However, a report claims the Duchess of Cambridge has a "strict style guide" she needs to adhere to during her second pregnancy.

According to Huffington Post's Anne Chertoff, being a member of the Royal Family requires Kate Middleton to adhere to a "strict style guide." Chertoff supposed the Duchess of Cambridge will stick to her "main style tenants" wardrobe for her maternity wear including a winter wardrobe. The latter is reportedly reminiscent of the fashion style she wore when she was pregnant with Prince George.

Additionally, Chertoff claims there are fashion rules Kate Middleton won't break. Citing Myka Meier, founder of Beaumont Etiquette, the number one rule the Duchess' style guide won't break is the length of the hemline. Meier claims the hemlines need to just fall slightly above the knee. "During this royal pregnancy, you'll find the Duchess predominately in dresses, less form-fitting than her norm," she said.

Chertoff claims the Duchess of Cambridge will never wear a mini skirt since she is quite conservative with her dress and skirt. However, New Zealand's Life and Style posted a photo of Kate Middleton wearing a thigh-slit Jean Packham dress that showed her enviable legs. The skirt on her dress was even described as having a "mini hemline."

Additionally, another style guide the Duchess supposedly must adhere to during pregnancy involves the showing of cleavage. Myka adds Kate Middleton is not likely to break another rule of showing her cleavage while she is pregnant. But then again, dubbed by Life and Style as a "pregnant fashion rebel," the 32-year-old could be seen revealing a bit of cleavage with her Jean Packham dress. According to the International Business Times, the Duchess wore the blue dress on Oct. 21 for an evening event since her return to royal engagements.

Kate Middleton has reportedly been experimenting on some sexy and sophisticated new styles for her second pregnancy. A source claimed her personal assistant, Natasha Archer, has been influential in her choices for maternity wardrobe. She has supposedly persuaded the Duchess of Cambridge to break some of her strict style guide, especially with the length of the hemlines. However, per IBTimes, the Duchess has the final decision when it comes to her wardrobe. The sexy dresses are believed to even be Kate Middleton's own choices.