Now, the girls are preparing to release their fourth album On Your Radar before embarking on their first ever UK arena tour.
Digital Spy caught up with Rochelle, Mollie and a now-visibly pregnant Una to talk maternity tour costumes and those US TV deal rumours.
Are you pleased with the reaction to 'My Heart Takes Over'?
Rochelle: "Everyone seems to be loving it!"
Mollie: "Yeah, really good. Sometimes with our videos people tell us they don't like them, but with this one everyone has been positive."
Una: "I think it was time for us to go back to ballads because we had released two uptempos."
The video looks seriously cold...
Una: "It was! There was severe wind and rain. Sometimes when it's freezing you can just cover up, but when there's that wind it's awful."
Rochelle: "It was really slippy. I was watching Frankie on set and she fell on the floor!"
You're releasing the track in a busy week - are you confident about its chances?
Rochelle: "The schedule is busy every week up until Christmas. If we had released it a week earlier we'd have been up against my boyfriend (Marvin Humes - JLS) and I don't fancy that!"
Una: "It's such a competitive week, but we have such a great fanbase and I'm sure people like the song. It's not always based on chart position. We're delighted every time we get a top ten. We just hope the single entices people to buy the album."
How would you describe your new album On Your Radar?
Mollie: "I would say it's very Saturdays, but there's evidence of a progression. At the minute there is quite a lot of dance music around and I think that's reflected on the album. There are also some great ballads, so it's a great pop album."
Rochelle: "We don't shy away from that mixture. The album is a progression and we co-wrote over half the album."
Having given it a few spins ourselves, there are quite a few different genres on there...
Rochelle: "That's why it's great making pop music because you're not limited to one sound. The album is not samey. We made an effort to keep it pop, but with variation."
Mollie: "When we were making this album we were really aware that we were taking it on tour and so we had to imagine what would go down well in an arena. That's what helped us pick our tracks."
Is there a particular track on the album you're looking forward to performing live?
Rochelle: "There are a few for different reasons. Ballad-wise we like 'Last Call'."
Mollie: "That will be really stripped back."
Una: "I think when it comes to the tour it's the singles that the crowd are going to get excited about and we already have 12 of those! It will be a good way of introducing our new album, though."
Mollie: "I'm really looking forward to 'Get Ready, Get Set' as it's outgoing and really fun."
There's a song called 'Faster' that appears third on the tracklist - does that mean it's a likely future single?
Rochelle: "No, not necessarily. It's a song that we really like. Before we pick our singles we want feedback from the album. We'll release one while we're on tour so we'll judge from the audience reaction."
Mollie: "We get a lot of feedback from the fans on Twitter, which is so interesting for us. We've worked with this material for a while, so it's nice to get a completely new opinion from the fans."
How did the collaboration with Travie McCoy come about?
Mollie: "Travie sent the track in and we were like, 'Oh my God! Travie knows about us?'"
Rochelle: "Me and Vanessa were saying earlier that we get sent a lot of tracks and it came through with all of the others and as soon as I heard the intro, 'Yeah, it's Travie', I was like, 'Sold!' So that decision was an instant for me as there's something about his voice. You know straight away that it sits."
Do you have your sights set on cracking the States? There are rumours of a US TV deal...
Rochelle: "There has been so much press flying around for weeks. It was literally us five girls thinking, 'We've done a reality show here - how fun would it be to do one Stateside?' And that's not necessarily us cracking America. Maybe it would be about us taking our material to a different environment. We literally had it down as an idea and then all of a sudden the press are saying we've got a channel that it's on. It was an idea, but all the confirmed stuff is untrue."
Una: "Mind you there are more grains of truth in this than there are in the two-year break rumours."
Una, congratulations on your pregnancy - how are you planning for 2012?
Una: "Aww, thank you! I'm just planning for now, at the moment. I haven't even bought a single item of clothing for the baby. I'm not due until the end of March next year, so it's still a way off. There's lots going on at the moment with the tour and the album and it's only growing quite slowly, so I'm just taking each day as it comes. I'll do what I can, but I definitely intend to become a working mother.
"I was sat in the doctor's the other day and spotted loads of magazines that I have never even thought about reading like 'Mother and Baby'. I picked one up and saw a feature about all the celebrity mums and how much maternity leave they gave themselves. It said Victoria Beckham took like two weeks, so that will probably be what it's like for me."
Rochelle: "It has fallen at a good time because next year - believe it or not - we'll be working on releasing another album. So it will be writing and recording time out of the public eye."
Have you had to make any special tour preparations around the pregnancy?
Una: "We still have to sort a few things out, but all the stylists and choreographers are excited to work with me because I won't be able to do full-on routines and my costumes will have to be maternity ones!"
The Saturdays release On Your Radar on November 21. The single 'My Heart Takes Over' is out now. Watch the official music video below: