Dr. Paul wrote on Instagram: "What does everyone think, boy or girl?!
"Hearing the heartbeat for the first time is such a beautiful experience... Sound On! #SundayFunday"
Last week, the couple announced that they , due in October.
Dr. Paul wrote: "I’m so excited & blessed to announce that my wife @brittanypattakos and I are bringing a new life into this world.. October can’t come soon enough to meet my first baby girl or my fourth baby boy (yes, it’s going to be a surprise for me)!
"All I know is I better get my diaper changing skills polished up.
"There is nothing like the feeling of holding a newborn, especially when it’s my baby."
Brittany recently shared some photos of her baby bump.
She wrote on Instagram: "Baby Bump at 13 weeks and 4 days!
"Thank you @kimkardashian @skims for the lovely outfit!
"So comfy!!!
"Next week I will be doing the gender reveal.
"What do you guys think it is?!"
Paul is famous for co-hosting the E! reality series Botched with Dr. Terry Dubrow.
The couple wed in September 2019 in front of 70 guests at St Nicholas Antiochian Orthodox Church in Los Angeles.
The pair celebrated again in Santorini, Greece, and the medical assistant told E! News: "Paul and I are incredibly grateful to have family and friends from around the world join us in the blessing of our marriage here in Santorini, Greece.
"To have so many loved ones is the greatest gift.
"The Greek people welcomed us with open arms and made us feel truly at home.
"The perfect weather and island made a spectacular backdrop for the moments we will cherish for the rest of our lives.
"This was the most exciting start to our marriage.
"We are so thrilled to share our lives together."
Paul was previously married to star Adrienne Maloof, but they divorced after 10 years of marriage in November 2012.
The couple share three sons together, Colin, Gavin and Christian.