The year 1948 yielded one of history’s great non-announcements: an opaque statement from Buckingham Palace that Queen Elizabeth II would undertake “no public engagements after the end of June.” That she was pregnant with her first child, Prince Charles, went wholly unmentioned.

In the intervening decades, things have gotten a bit more explicit — and lucrative. The news that a public figure is pregnant often comes directly from the source, in a post that may also be an #ad.

The most obvious brand partners in this area are purveyors of pregnancy tests. Clearblue has worked with upward of 70 celebrities and influencers on endorsements of its products since 2013. First Response has sponsored pregnancy announcements, too, including ones by the singer Kelis and the ballroom dancer Karina Smirnoff.

Other companies, like Belly Bandit (which sells maternity wear), Enfamil (the formula maker) and CBR (a cord-blood banking company), also make deals with celebrities around pregnancy and other parenting milestones.

When Audrina Patridge of “The Hills” announced her pregnancy on Twitter in 2015, her words were accompanied by a photo reminiscent of a 1950s advertisement for laundry detergent: pleasant partial smile, product (a Clearblue pregnancy test) positioned on a diagonal with the model’s shiny eyes and, of course, some copy to hammer the point home (#babyontheway).

“It was a very clear, easy way to announce to the world and let everybody know at the same time that you’re pregnant, because it says ‘pregnant.’ You’re holding it,” Ms. Patridge said. (Still, it seemed to confuse her reality co-star Spencer Pratt, who was unsure whether the post was an ad or personal announcement. Today, we take for granted that celebrity baby posts can be both.)

Iskra Lawrence, a British model with four million Instagram followers, told her management team that she’d seen the paid announcement posts and was interested in doing one herself. She shared her news in late 2019 with First Response and donated $20,000 — most of the fee, she said — to two followers experiencing infertility; the post was, at once, a P.R. blast, an ad and an awareness campaign.

The amount of exposure a brand will get by sponsoring a pregnancy announcement is “exponential,” said Sarah Boyd, a vice president at Socialyte, which brokers marketing deals for influencers and celebrities. The fee depends on “their fame and their relevance at the time,” she said, and likely diminishes after their first child. Ms. Boyd estimated that someone like Kylie Jenner could ask for more than $1 million.

But for many stars, the decision to post at all is fraught with questions about control, influence, labor and privacy.

‘People Want More and More of You’

These brand partnerships reinforce the idea of motherhood as defined by consumption and spending, said Renée Cramer, a professor of law, politics and society at Drake University and the author of “Pregnant With the Stars: Watching and Wanting the Celebrity Baby Bump.”

In her book, she explains the way celebrity mothers become “branded exemplars of how ordinary people can and should live.” When we see a celebrity holding up a certain brand of pregnancy test or diapers, Dr. Cramer said in an interview, it reminds “average people that, well, this company belongs in your nursery, even if there’s no good reason for it.”

Ellis Cashmore, a visiting professor of sociology at Aston University in Birmingham, England, and the author of “Kardashian Kulture: How Celebrities Changed Life in the 21st Century,” noted that celebrities have already licensed their names to perfume lines, turned their lives into smartphone apps and sold their time on apps like Cameo. “It’s only logical to expect that they are monetizing a life before it becomes a life,” he said.

Nicole Polizzi, who came to fame as Snooki on the MTV show “Jersey Shore,” has watched the tide shift on celebrities navigating this part of their public lives. She announced her first pregnancy in 2012 on the cover of People magazine. “Back then it was such a big deal,” she said. “By the third, you’re just like, ‘Right, Instagram post. Here it is.’”

The public once wrestled with the notion of celebrity moms oversharing. Now, fans want to know the sex, the name, the due date. Paparazzi are stationed outside of maternity wards. In a world that is always on baby bump watch, the celebrity has two options, Dr. Cramer said: “I can try and control the image, or I can profit some way.”

Babies are expensive, said the actress Danielle Brooks (best known for her role on “Orange Is the New Black”), who ultimately felt joyful about teaming up with Clearblue to announce her pregnancy to the world in late 2019. “You have to do what is right for your family.”

There is also pressure as an online figure to “keep creating content” to build your following, said Ms. Lawrence, the model. After birth, she said she felt a “tug of war” between wanting to be present with her baby and wondering: “Is this something that I should capture just in case?”

“People want more and more of you,” said the author and actress Jenny Mollen, who is married to the actor Jason Biggs. She has talked about postpartum bladder leakage, Grave’s disease, Botox and her placenta; she announced her second pregnancy with a baby product company in a five-figure deal, she said.

Dr. Cramer said this continuing sharing is “double performative labor.” The celebrity not only carries out the reproductive and care-taking labor of motherhood, but also transmits a performance of that identity to followers.

Even celebrities who keep a lid on their pregnancies must strategize the eventual rollout of their child. On Aug. 26, UNICEF announced the birth of a baby to Katy Perry and Orlando Bloom on Instagram. (Ms. Perry had announced her pregnancy in a music video.) Ms. Perry then reposted the Unicef link; her post was liked by more than 5.5 million people.

The Private Becomes Public

Pregnant people famous and not grapple over the timing of these announcements. Conventional wisdom is to wait until at least 12 weeks before revealing a pregnancy, though second- or third-trimester pregnancy loss is still possible. When a publicly announced pregnancy is lost, it becomes a much bigger story, said Dr. Cashmore.

Takiema Bunche-Smith woke up in her Brooklyn home on Oct. 1 to direct messages from friends warning her that she may find social media triggering that day. Chrissy Teigen had just posted photos portraying the loss of her third child with John Legend, and social media was overflowing with both sympathy and criticism.

Ms. Bunche-Smith’s first child was stillborn at 37 weeks and two days in 2003; at the time, talking about such a loss felt taboo. She found Ms. Teigen’s post powerful. “The photos were so poignant and bittersweet and such a clear example of what every one of us experiences,” she said. (Ms. Teigen noted in a Medium essay that the responses she received from followers were overwhelmingly kind, and that they helped her through an impossible time.)

“You worry about upsetting other pregnant women, you worry about how your loss will affect them,” said Georgina Brackstone, a 40-year-old jewelry designer in London who lost her first daughter 33 weeks into pregnancy nine years ago. She said public figures like Ms. Teigen had “allowed people like me to talk about their experiences.”

Elizabeth Cordero, a Los Angeles hairdresser who has had multiple miscarriages and lost her baby seven days after birth, said there is no “safe” date after which to announce. She is halfway through a pregnancy and said that “this time around, we’ve decided that we’re just going to celebrate every damn day.”

In situations where there are birth complications, difficulties breastfeeding, perinatal mood and anxiety disorders, or bladder leakage, celebrities now seem more inclined to share this too, with the hope that their openness may help someone else.

“If they are doing a public service, or they believe that they are, in talking about a product, there are women who will benefit from that message, whether or not it’s paid,” Dr. Cramer said.

It is assumed that the sharing also benefits the author, something Ms. Mollen has begun to question. “The more of ourselves we give away, the more the more we’re sort of rewarded for it, and that’s a slippery slope,” she said. “It’s all performance, even the stuff that you’re saying: ‘This is real. This is my real life.’”

In April, Ms. Lawrence welcomed her baby with her partner, Philip Payne, who is a music executive. When her followers wanted to know about her at-home water birth, she shared a video of that. It seemed important, she said.

Now, she’s not as sure about putting it all on Instagram. “The aim is to be more in control of my life and future and career,” she said. “Having it so much reliant on social media feels unstable.”