Three months after Meghan Markle married Prince Harry on May 19, British booking agencies are offering super short odds – around one to five – that the new duke and duchess will become parents in 2019.

If that happened, 37-year-old Meghan would be one of the oldest first-time royal mothers in history, which has made Windsor watchers expect a baby announcement sooner rather than later.

Desperate to get the jump on any news, the Express newspaper has claimed “there could be one telltale sign in the Duchess of Sussex’s appearance if and when she is expecting a baby”.

A more obvious one would be a baby bump, but the Express went with Meghan’s hair suddenly reverting to its natural state, described by the former Suits star herself as “densely curly”.

To counteract that, she admitted in 2011 to using a semi-permanent hair straightening treatment to achieve her signature bouncy look.

“My mum is black and my dad is Dutch and Irish, so the texture of my hair is densely curly,” Meghan said.

“I’ve been getting Brazilian blowouts for a couple of years.”

A Brazilian blowout is a semi-permanent professional straightening technique.

It’s just one tool in Meghan’s war on curls, which seemingly began when she was in her mid-teens, if her high school photos are any guide.

Earlier this year, her former stylist Lydia F Sellers told Refinery29 the duchess augments her Brazilian blowout regimen with the Kérastase Oleo Relax collection for frizzy hair, Oribe’s volumising spray and Kevin Murphy’s Smooth Again lotion.

If Meghan is using a chemical treatment now, “As soon as she gets pregnant she will no longer be able to use those same products, which could be very interesting,” according to royals watcher and etiquette expert Myka Meier in The Sun.

Intriguing theory – bun watch rather than bump watch – but probably not true, according to Australian hairdressers.

“Treatments like that used to have a cancer-causing agent called formaldehyde in them, which isn’t allowed to be used anymore,” Tess Wilks, senior stylist at Rubi Hair in Melbourne’s Malvern, told The New Daily.

The salon specialises in straightening treatments, which cost between $250 and $450.

“We have something called a keratin straightening treatment, which is definitely OK to have done during pregnancy,” Ms Wilks said.

The basic procedure that Meghan may be having takes up to three hours.

It includes washing the hair with a special shampoo and a treatment that is left on “for up to an hour, depending on the frizziness of the hair,” Ms Wilks said.

There is an alternative, slightly stronger treatment.

The Duchess of Sussex at an August 4 wedding in the UK. Photo: Getty

According to Ms Wilks, Meghan might be having a keratin treatment every three to four months, and probably has a hot blow dry every day or two “to keep her hair nice and pristine”.

“That would smooth it out quite nicely,” she said.

“Her hair looks quite manageable and it definitely looks like she has a lot of blowouts rather than using a hot tool.”

But while some treatments have cleaned up their act, in 2011 the Environmental Working Group published on its eponymous site a warning into Brazilian blowouts and similar treatments during pregnancy.

Called ‘Flat Out Risky’, the report claimed that of 16 companies it investigated, 15 brands “admit to little or no formaldehyde. Tests show their products contain substantial amounts”.

Last year, US cancer foundation Live Strong claimed on its website that keratin products temporarily change the structure of hair and “may have an effect on your unborn child”.

The choice to use any products on your hair during pregnancy “is a very personal preference,” a staffer at Melbourne’s Saint Louie Hair – which doesn’t do Brazilian blowouts – told The New Daily.

“Some women decide not to colour their hair, for example, but some are fine with it.”

When contacted by The New Daily for comment, a spokesperson for the the Royal Australian and New Zealand College of Obstetricians and Gynaecologists said the college had “no guidelines” relating to hair products.

“I don’t think we have any research and definitely nothing we have published that says it’s safe or unsafe to use hair products,” the spokesperson said.