DailyMail.com has contacted a spokesperson for the Kardashian family for comment.
The two stars shared the baby news at the same time on Friday by posting an emoji of a pregnant Blac Chyna to Instagram, and the mom-to-be was spotted out in LA after the big announcement.
The 27-year-old was seen talking on the phone as she stopped by a gas station with a friend on Friday afternoon.
Pregnant Chyna was wearing pink lip gloss, and kept a low profile in a black jacket and pink baseball cap, while flashing her dazzling diamond engagement ring.
An insider close to the couple told DailyMail.com on Friday that the pair are "very happy and excited", noting that both families have known about the pregnancy for some time.
"Chyna's family is very supportive," the source added.
The insider also revealed that the couple are planning a "very big wedding", but are yet to pin down an exact date.
Chyna's former fiancé Tyga has been dating Rob's half-sister Kylie Jenner since last year, leading to a feud between the model and the Kardashian-Jenner family.
This will be a first child for 29-year-old Rob and a second for Chyna, who has three-year-old son King Cairo with Tyga.
The 26-year-old rapper posted "congratulations" on Chyna's pregnancy emoji on Friday.
The Kardashians are yet to comment on the news, although Kim 'liked' both Rob and Chyna's Instagram posts and Kylie 'liked' Rob's.
Meanwhile Chyna's mother Tokyo Toni shared her excitement in a video posted to Instagram, revealing: "I just got off the phone with my daughter Blac Chyna and son-in-law-to-be Rob.
"Congratulations, guys! They told me, 'You're about to be a grandma.' I'm super excited for them and I cannot wait for this new addition to the family."
She added: "As well, I'd like to congratulate the other side of the family which are the Kardashians and the Jenners. Congratulations guys, we're having a baby! I'm going to be a grandma!"
Rob and Chyna, real name Angela White, went public with their romance on January 25, and they announced their engagement in early April.
The reality star popped the question with a $325,000 7-carat diamond ring in front of his future wife's whole family.
After they got engaged, Chyna's rep said she will be taking Rob's name, sharing: "She's soon to be Angela Kardashian. She's ecstatic."
In February, Rob drove for 26 hours to collect Chyna in Texas after she was arrested for alleged public intoxication and drug possession at Austin airport.
According to legal documents obtained by DailyMail.com, police found two white and gold ecstasy pills inside a sunglasses case in Chyna's handbag, although she insisted she had no idea how the got there.
Rob's romance with Kylie Jenner's love rival caused a huge family feud with the Kardashians, and his famous sisters and mother Kris did not publicly congratulate him on his engagement.
Khloe even kicked Rob out of her home after learning of their romance, noting he'd "burned his last bridge".
A source told People: "Ever since Khloe found out that Rob is dating Blac Chyna, she felt betrayed. This feeling has never changed. After finding out about the engagement, she is furious at the lack of respect."
In a recent episode of Keeping Up With The Kardashians, Kris told daughters Kim and Khloe to 'f*** off' after they said she shouldn't be paying for Rob's home.
The momager splashed out $2.3million on a four-bedroom house in Calabasas for her only son in February, according to Entertainment Tonight, which he is now living in with his future wife.
Last month, Kylie and Chyna put their differences aside and called a truce, sharing selfies to Snapchat while hanging out together.
And Rob was thrilled, posting one of the photos to his Instagram page with the caption: "So happy my girls finally got to talk and make peace! #MyFamily #AllLove."
Meanwhile Kim Kardashian, who is said to have instigated the get-together between Kylie and Chyna, was spotted spending time with her brother and future sister-in-law last week.
In January, Rob taunted his family by pointing out that Chyna would one day give birth to the only baby to carry the Kardashian name.
The star shared a meme of the model which showed her carrying a car seat, along with the words: "Blac Chyna probably out shopping rite [sic] now as she plan to give birth to the only next generation of the Kardashian name."
Chyna's mother said in a recent interview that she expected her daughter to get pregnant right after marrying Rob.
"I want another grandchild, for sure. It's very likely to happen after the wedding," the 45-year-old said, adding that the Kardashians will have to put aside any ill feelings when Chyna has Rob's baby.
"At the end of the day, they're all not going to have a choice if children come into play," Tokyo, real name Shalana Hunter said. 'At that point, Kris and I will be that child's grandmother.'
Chyna chose to announce the pregnancy news with an emoji hours after it was revealed that she is launching her own emoji line, following in the footsteps of Kim Kardashian and Amber Rose.
Her relationship with Rob has clearly had a profoundly positive effect on him.
Before going public with their romance, the sock entrepreneur was reclusive while battling depression and weight gain.
Rob has since slimmed down a huge amount, and his bride-to-be has been putting him through his paces with a strict training regime.
While the happy couple have yet to reveal a wedding date, Us Weekly reports that they plan to tie the knot "at the end of the summer" in a warm climate.
It's unclear if Rob and Chyna will cash in and have a televised wedding, but TMZ has claimed they are considering starring in their own reality series which would see them earn between "$150,000 to $200,000" per episode and $500,000 each for a wedding day special.
