"More commonly pregnant women will retain fluid in the legs and the ankles and feet, but they can also retain it in the hands and the face."
Dr Nestor adds: "It is not uncommon for women, particularly those in their second and third trimester to wake up one morning with swollen lips."
Fans have been commenting that the star's pout looked "different" while one joked that they had gone "from Cameron Diaz to Jay Z".
Twitter user Tiara wrote: "Wow Beyoncé's pregnancy lips. She gotta figure out how to keep them without getting fillers."
Beyoncé recently cancelled her upcoming Coachella performance in April leading some to speculate that she is further along than previously thought.
Previous estimates had put her due date at anywhere between April and July, and the couple, who are already parents to Blue Ivy, five, have yet to announce the twins' gender.
Beyoncé and Jay Z, 47, broke the internet with news of their new arrival on February 1 by way of an Instagram picture of the expectant mother cradling her baby bump.
She wrote: "We would like to share our love and happiness. We have been blessed two times over. We are incredibly grateful that our family will be growing by two, and we thank you for your well wishes. - The Carters."
In 2013, Beyonce revealed she had suffered a miscarriage prior to the arrival of her daughter.
Speaking in her TV show Life Is But a Dream, Beyonce said: "Being pregnant was very much like falling in love. You are so open. You are so overjoyed.
"There's no words that can express having a baby growing inside of you, so of course you want to scream it out and tell everyone."
