When Arielle Haspel posted a photo of her baby bump to her 20,000 followers on Instagram in September, it didn’t take long for the business opportunities to start rolling in.

The 33-year-old wellness blogger, who’s currently six months pregnant and lives in the Flatiron District, regularly nets anywhere from $250 to $5,000 to promote health and fitness brands on her blog and social media accounts. But since her announcement, she’s received more offers than ever.

“Now, there’s a new highchair company, a baby-stroller company and an organic baby food brand that have reached out to me [for potential partnerships],” says Haspel.

While celebrities with huge followings are getting paid big bucks for their bumps, a growing legion of lifestyle bloggers and social-media influencers are also experiencing a windfall of cash. According to BET, Blac Chyna and Rob Kardashian were reportedly paid more than a million dollars to let E! document daughter Dream’s November birth for a TV special, which will air on Dec. 18.

Haspel is still negotiating the terms of her upcoming sponsorships, but other moms-to-be have received gifts, trips and more just by showing off their growing bumps.

“It’s actually crazy, because I never thought I’d be getting job offers while I’m nine months pregnant,” says Marisa Megan, a 28-year-old wellness-travel blogger who works under the name the Hotel Yogini.

Last week, the Far Rockaway native posted a photo of her and her bump surfing at Encuentro Beach in the Dominican Republic. Megan saw a 330 percent spike in web traffic on her platforms (where she has up to 15,000 visitors every day), and since then has been contacted by family-friendly hotels and maternity brands for possible collaborations. She’s received more than $2,000 in gifts, including complimentary stays at both the Hotel Villa Serena in the Dominican Republic ($110/night) and Fazenda Catuçaba in Brazil ($300/night), and 15 yoga mats from B Yoga, which retail for about $80 each.

Small-business owners like Stephanie Manganelli, founder of Hoboken, NJ-based maternity-wear brand Stowaway Collection, say that it’s more cost-effective to dress a mommy blogger than a pregnant celebrity, since customers are more likely to relate to the former.

Manganelli gifts social-media influencers her dresses, which range in price from $65 to $125, in exchange for posting the outfits on their Instagram feeds.

“It’s the best advertising because you have real-life people looking fabulous in your clothing,” Manganelli, 32, tells The Post.

“It’s not a fashion model on a screen, it’s someone who is relatable, who has shared her whole life. If they’re wearing the clothes, you can picture yourself wearing the clothes too.”

But not everyone with a bun in the oven and an Instagram handle can make bank. Manganelli says that the mom bloggers she’s worked with all have at least 1,000 followers on Instagram.

And while it may look like these moms-to-be do nothing but take pretty pictures for free stuff, the work that comes with curating your life for an audience can be exhausting.

Jordan Rhodes, who owns online travel guide Glimpse and is eight months pregnant, spends up to 30 minutes taking and editing the perfect image to keep her more than 4,800 followers entertained. In return, she’s received up to $500 worth of bump-influenced gifts, including a $74 dress from fashion boutique CPC Childrenswear and a $275 wrap from clothing brand Covey Charleston.

“One bad photo could mean people will stop following you,” Rhodes tells The Post. “I have to take dozens of photos to get the perfect one.”

But she says that the pros of building your brand and making money on Instagram outweigh the cons.

“I think we’re also helping other women find ways to get through their own pregnancies,” Rhodes tells The Post. “If someone is having a tough time with her pregnancy, it gives her motivation to live her life and enjoy the pregnancy . . . no one wants to sit and stare at their TV all day.”

Which begs the question: Are these pregnant women exploiting their kids for monetary gain and social-media fame before they’re even out of the womb?

Megan, for one, thinks it’s “quite silly” for people to criticize mommy bloggers for cashing in on their pregnancies.

“Until paid maternity leave is available to every freelancer in the world, I think it’s a fantastic opportunity to continue to work while pregnant and do something authentic.”