ALEX JONES' description of what happens when you have a baby is pretty blunt. "It's like a bomb going off," she declares, before adding wryly, "in a brilliant way."

The One Show presenter, best known for interviewing celebs live on telly every weeknight, alongside co-host Matt Baker, became a mum for the first time last January, aged 39.

Now 41, she says: "I'd got myself together in terms of career, I know where I am, and then a baby comes. It leaves you in this new-fangled situation where you don't really know where to start," she adds, remembering the sensation of her world being thoroughly scrambled in the wake of pregnancy.

While lots of new mums are trying to piece together some semblance of sleep and get to grips with breastfeeding, Jones also spent the first chunk of her son Teddy's life writing down everything she was going through.

The result is Winging It!, her first - "and last!" - book.

Broken into three portions, it tackles life before the birth, after it, and then what happens to the rest of your world once you've just about got to grips with being responsible for a tiny human.

Jones felt there just wasn't enough information about fertility and pregnancy out there for would-be parents in her and her insurance broker husband Charlie's age-bracket (pushing 40). In 2016, she made a documentary for BBC One called Fertility & Me, and she says the research involved helped inspire her book.

"I wasn't sure how much I believed all the headlines, about how at 35 your fertility falls off a cliff," says Jones. "I do still think it's very much on a case by case basis, everybody's body is different, and some people who are in their Twenties struggle to get pregnant - it's not something that's just confined to people who are older."

However, during filming, a scientist explained to her how eggs deteriorate as a woman ages, and while doing a form of IVF, showed her the moment they introduce the sperm, via injection, to an egg. "In this case, they injected an egg from a 36-year-old woman, and the whole thing just crumbled," Jones recalls. "That was the biggest wake-up call to me, that that could be the case. That was the image that stayed with me and made us definitely think, 'We need to crack on with this if we're serious about having a family'."

Luckily, they didn't have any problems conceiving Teddy. "It was very straightforward. But for a lot of friends, unfortunately, that's not been the case. I thought it was important to open up that conversation," says Jones.

That conversation plays out in the book, with Jones also looking at how a baby affects your relationship, how difficult she found motherhood to begin with, and what it's like - just as you're hitting your career stride - to be a woman and have to "biologically take your foot off the gas, take a step back and actually have the baby".

"At the heart of the book is a lot of honesty," says Wales-born Jones, who has presented The One Show since 2010, and is particularly frank about the decisions she had to make around maternity leave and finding the right time to get back on the BBC's green sofa.

"I have a big respect for the job I do, and what comes with having respect for the job you do is a fear of losing it," she says. "I love my job, and sometimes I think women find it hard to admit they want to go back to work because they like it.

"People assume you should be saying, 'Well, I want to stay at home because I love my baby', and of course that is the case - I absolutely adore Ted - but I do like my job as well.

"There's nothing wrong with saying, 'I've worked hard to get to this point and yes, I want a child, but I also want a career', I think that's fine," she adds powerfully. "Men never have to struggle to say that, I don't think women should either."

She admits that "finding the balance is difficult", but notes: "It's not just about liking your job, it's about necessity; lots of us have to go back because it's necessary for us to earn a living and for lots of families, it does take two wages to bring up a child."

In the end, Jones went back to work three months after Teddy was born. "There were some concerns, mostly from my mum and friends, who said, 'Are you sure, Al, that you're ready to go back, it seems quite soon?' And of course, before you have a baby you don't know how soon that is. I'd made promises before really knowing how I would feel."

Fortunately, she had a "super supportive" boss, who suggested she come back part-time to begin with. "It worked really well, but I'm not scared to say I was worried about taking maternity leave - it's scary taking time out."

While Jones didn't suffer any pressure on the coming-back-to-work front, she says being pregnant, whether inside or outside the studio, did involve an outpouring of advice and opinions - whether they were always welcome or not.

Sure, it was great to have Tom Hanks recommend her hypnobirthing books ("Oh gosh, he was so nice, one of the nicest guests we've ever had"), and Jamie Oliver tell her to stash some takeout menus for ordering from at the hospital ("The guests all gave their two pennies' worth, which was lovely"), there was no escaping the fact that "everyone has an opinion" when there's a baby involved.

"Everybody feels they can give you bits of advice and tips, and most of them, to be fair, are great," Jones notes, "but they do feel they can make comments they probably wouldn't otherwise, in the same way they feel they can touch your bump - you wouldn't normally walk up to someone in the street and touch their stomach, that would just be plain weird, but for some reason when you're pregnant, they feel they can."

Back at work full-time, and having raised almost £800,000 for Sport Relief with her Mother Of All Challenges recently - five days of biking, hiking and open water swimming - her tactic for dealing with unasked-for guidance, no matter the situation is: "Ignore, polite smile, move on."

After all, pushiness isn't solely reserved for pregnant people. "When you get a boyfriend, people ask, 'When are you going to get engaged?' When you're engaged it's, 'When are you going to get married?' Then it's, 'When are you going to have your first child?', and now it's, 'When are you going to have your second?!'

"People are always looking for that next thing, speeding through life," says Jones, sounding slightly incredulous. "There's so much expectation on people, and sometimes that pressure is quite hard to deal with."

Winging It!: Parenting In The Middle of Life! by Alex Jones is published by Lagom, priced £14.99 (ebook £6.47). Available now.