Jennifer Lopez is in a simple dress, long bare legs outstretched in front of her. Her voice is creaky with a chest infection, her eyes bleary. But her work ethic is as strong as it was back in the Bronx days she immortalised in her 2001 hit ‘Jenny From the Block’. It’s been a long time – and many blocks – since the tough, determined girl born to Puerto Rican parents danced her way around Manhattan as a backing singer for the likes of Janet Jackson and Paula Abdul, and there seem to have been many Jennys since then too.

We are in a sunny Beverly Hills hotel room. It is not a suite. There are no Diptyque candles. And the thread count on the bed linen is probably not more than 420. It certainly doesn’t meet the stipulations she was alleged to have demanded of her accommodation when she was J Lo the diva, who routinely rode in Bentley convertibles with her fiancé Ben Affleck, or went to gangsta-style clubs with her partner of two and a half years Sean Combs (P Diddy), and was chased by paparazzi.

Life is quieter now, with her husband of five years, Latin singer Marc Anthony, and two-year-old twins Emme and Max, but it’s certainly not simpler.

‘I just did two 24-hour flights back to back for a party in Kazakhstan that I had to perform at.’ Was it worth it? ‘I wouldn’t have gone otherwise. Totally.’ The result is that she’s feeling exhausted and fluey, but she’s a trouper. She’s known worse (such as the trauma of cancelling her wedding to Ben Affleck hours before it was due to take place in 2003).

Her life has certainly changed pace. And her new movie The Back-Up Plan reflects that. It’s about a woman who decides that she doesn’t want to miss out on having children even though she doesn’t have a boyfriend. So she plans to have IVF and a baby on her own, and on the same day as the treatment she meets a man with the kind of romantic possibilities that she’d given up on. They fall in love and everything happens in reverse. Instead of romance, proposal, marriage, baby, it’s – she’s already pregnant with somebody else’s baby, then romance, then relationship.

The movie is cutting-edge funny and a return to form for Jennifer. ‘It couldn’t be more perfect,’ she says, ‘the whole idea, in a romantic comedy, that the pregnancy is the obstacle. It’s always, “Oh, my boyfriend can’t commit, I can’t commit, I’m in love with my best friend.” But this story seemed to me to be about a real problem. “Are you going to take on this child? Is it OK to ask somebody to do that?”

Does she think she would have used IVF to get pregnant if she hadn’t met the right man? She shakes her head. ‘It takes a lot of bravery to have a child on your own. I have a girlfriend who did it and I really admire her. Especially knowing how much help you need. It’s a lot to be a working mum and think, I’m OK on my own. I would like to think that I’m strong enough to do that, but honestly, I don’t know if I could.’ Several aspects of pregnancy come across.

In the movie she gets pregnant with twins – how much like real life is that? ‘Well, that’s very real life. I loved it. The woman who wrote it had just gone through a pregnancy, so it was all very fresh in her mind. And it was very fresh for me – the twins were about a year old.’

Several aspects of pregnancy come across in the movie as funny, gross, horrendous, embarrassing. Were they aspects she related to? ‘All of it. I wanted to put as much in as we could that was real: the overeating, the burping. Why not? It’s funny too. Pregnancy and giving birth are weird, strange. The growing life inside you – it’s like an invasion of the body snatchers.’

Jennifer did not have IVF herself. ‘A lot of people thought I did because I had twins, but what they don’t realise is that when you are over 35 the chance of twins increases, especially if they are in your family, and they are in mine. I was 37 when I got pregnant, so I had both factors going on.’ She knew she was having twins at seven weeks. ‘I didn’t believe I was pregnant, even though I had taken a pregnancy test. The plus sign didn’t look dark enough and I kept thinking that maybe it wasn’t a good test, so I called the doctor, who said I should come in and check. And then she said, “Oh, it looks like you’re having twins.” It was a big shock.’

But also a joy. Jennifer had been broody for years. Almost as soon as she got together with Marc (in 2004, a few months after the broken engagement with Affleck and after Marc’s separation from his first wife, former Miss Universe Dayanara Torres), she realised that their relationship was more bonded and grounded than previous affairs; they came from a similar place, both in touch with their Latin roots. The turbulence that had defined her love life with Affleck and Combs gave way to something else. She had already been married twice, first in 1997 to waiter Ojani Noa (an 11-month marriage that was eclipsed by her huge success with George Clooney in Out of Sight) and then in 2001 to dancer Cris Judd, whom she hoped would provide her with the mix of stability and edge she needed (they divorced in 2003, after Jennifer got involved with Affleck). But with Marc, she says, ‘it was the type of relationship that you dream about. You get to the point where you realise what’s real and what you are imagining to be there. It takes a lot of looking and getting past the disappointments.’ With Marc it seemed right to start a family.

How has she changed since becoming a mother? ‘I think it calms you down a little bit, even though you have less sleep. Everything is at hyper speed, which puts things into perspective: this is important, this is not important, this is something that can wait, this is something I need to take care of. You speed up your decision-making process and you prioritise in a different way.’ Jennifer redefined the way women think about their curves by never being afraid to display her tiny waist and wide, full derrière. She was used to having a dancer’s body – flexible, toned, sculpted. Losing that must have been difficult. ‘Yeah, I do remember distinctly when you don’t fit into your clothes any more. At first it’s cute when you have a little bump. You wear big sweaters. Then one day your jeans don’t fit and you think, oh no, it’s happening. I was on tour until I was six months pregnant, so I didn’t grow the way I would have if I had been sitting at home, but once I was just sitting around, that’s when I got really big.’ How long did it take her to get her body back afterwards? ‘A while, a year. Six months afterwards, I did the Nautica Malibu triathlon and I was still 16lb overweight. Over the next six months I got it back.’ Was there a strict regime? ‘No. I don’t get too crazy any more. There was a time when I really worked out, but I was never manic about it. I did what I could. I’ve got good genes. But I care less now.’

In the movie, her character Zoe craves junk food all the time. ‘I’m not a junk food person. I like food, though. And you do feel very hungry. Your body is asking for food. The baby is asking for food. It’s like a factory. That’s why I made the decision when I was eight months pregnant to do the triathlon after I had the babies. I wanted to know I was the same person as before I had them. I wanted to be that person more than ever for my babies. I wanted them to be proud of me. I wanted them to think, “I’ve got a special mum, she was amazing, look what she did!” I didn’t want to lose my ambition and drive to do amazing things.’

She always defined who she was by how hard she could work and how much she could love. How does she still work so hard and fit that in with the demands of motherhood? ‘I want to be the best at that too. I want to just do it all. When we travel we travel with the babies. I try to rehearse in the house. I’ve adjusted my life so that I can spend as much time with them there. I’m lucky to have that luxury so I’m going to use it to the fullest.’

Is she ready for another baby yet? ‘No. I think I just need to work right now. I do want another baby, because once you have one you realise what a blessing it is; what an amazing miracle and how much they enrich your life. But you still have to be an individual.’

Do the twins have a special connection? ‘They do. Max is always climbing out of his cot to get in Emme’s. But then they fight like cat and dog. And I’ve figured out the difference between men and women by seeing their innate characteristics. She is very careful, and you can see her thinking; men don’t think, they attack and deal with the consequences. We approach life and love in different ways.’

‘He is still that, and I’m the biggest challenge that he’s ever had to deal with, and that’s what keeps it interesting for us both. John Cassavetes [the director and actor] once said that he and Gena Rowlands battled their whole marriage. There was an intensity in their relationship. He said that in some ways they both knew that if the battle was over the.

Her own love life used to be like a roller coaster – enormous highs of passion with lows of betrayal. How does that translate into her relationship with Marc? Did she suddenly settle and find that stability suited her?

‘For all the stability we provide for each other, Marc and I are both artists. We both like intensity. We are both very passionate, and that still exists in our relationship. If we didn’t have that it would be boring. Too boring for me.’

She once told me that her perfect type of man was not a straightforward bad boy but a boy who was a perfect mixture of hard and soft. A little bit stubborn, a little bit of a challenge; you had to work to get to the sweet bit. Does Marc fit into that ideal? Is he still that? Hard and soft? relationship was over. They cared enough to battle.

‘People seem to think that when there’s conflict in a relationship it’s always a bad thing, but I think you need a challenge. The dynamic between us is passionate and that’s why it works. We are compatible, but at the same time we are different enough to make it interesting.’

I tell her that I’ve read a couple of stories recently that said they are different enough to be splitting up. Has she read those? ‘Of course. It doesn’t really matter to me. We know what’s true.’

Jennifer’s relationship with fame has completely changed since the early days. She used to think success equalled fame, which meant a constant accompaniment of paparazzi and tabloid fever. Then she realised artistic credibility came from getting on with it and headlines didn’t make a relationship work. But she’s used to controversy, to stories spiralling out of control, and seems pretty unflustered by it.

She hasn’t read the story about her first husband selling their wedding photos, she says (although there have been reports in the press that she’s suing him over it). ‘Somebody asked me about it recently but I didn’t see it. I’m not in touch with him at all.’ Is that your decision or his? ‘It’s just your life goes into different chapters. It’s like the first grade. You just get past it.’

What she doesn’t want to get past is the experience of love. All the different kinds of love she’s had – fierce, warm, treacherous; how to keep love going; how to stub it out if it’s bad. ‘I’m putting all that into a new album called Love?, because I still find love very confusing and challenging. I also feel it’s time to open up the dialogue about what that word ‘love’ means, what do people do in love? Should we have better standards in love, [agree that] it’s not OK to be dishonest, to cheat, or be pointlessly cruel?’

Isn’t it becoming more and more difficult to juggle children, acting, music? Does she feel she should decide to go in one direction?

‘Oh no, I’m not ready to do that.’ What about the crop of new girls that are storming the charts – does she feel threatened by them? ‘No, I love all the girls out there now – Beyoncé, Rihanna, Carrie Underwood, Pink – all of them. I don’t feel in competition with them. I just want to be me. And that’s always been good enough.’

Was reaching 40 last year a watershed birthday? ‘It was the best party of my life and the best year so far.’ So she doesn’t worry about body parts moving in the wrong direction? ‘Not yet.

Somebody told me 45 is when that stuff happens. So maybe I can hold on for a while.’ What she’s really holding on for at the moment is a small part on the hit TV show Glee. ‘I’d just like to do an appearance because I love the show so much. It’s one of my favourites.’ But as well as her new movie, her new album and her ambitions for television, her social life in Miami is pretty full-on. Her husband owns part of the Miami Dolphins American football team, and they are also soccer fans and friendly with the Beckhams. Victoria commented recently that they were the same dress size. Jennifer’s eyes widen in shock at this. ‘I don’t think I could fit into her dresses. She’s a tiny thing,’ she says. ‘But she could certainly fit into mine.’

Jennifer Lopez