The weather presenter says colleagues on the show, including Dr Hilary Jones, kept it from her that she was going into labour and helped keep her calm before her delivery at 27 weeks. Her daughter Charlotte is now four.
Tobin said because she felt 'superstitious' about buying any clothes or doing any decorating before her third trimester, her ASOS delivery of maternity clothes arrived on a day she began feeling a bit ill.
Tobin told her husband: "'I'm gonna go to bed and have a bath, I feel a bit tired and bit achy.' And then the next day I had her. So I never even wore any of my maternity clothes."
WATCH: Laura Tobin on going into premature labour at Good Morning Britain
Saying she was 'lucky' she had gone in to work the next morning because she ended up at St Thomas's hospital with the 'best' staff, she told Kate Thornton on White Wine Question Time that on first seeing her, the show's stylist Debbie Harper told her she looked 'terrible'.
Convinced she was having Braxton Hicks contractions — or false contractions that some women experience — Tobin told colleagues she wanted to have her hair and make up done and record some weather segments but they called her 'crazy'.
Harper — who Tobin called 'the infamous Debbie Dresses' — called Dr Hilary who was on his way in to the studio as well and told Harper not to tell Tobin that he thought the baby was coming, that he would phone the hospital and 'sort it all out'.
Tobin said: "And then Piers [Morgan] came running past and he was like: 'Oh my god, it looks like she's gonna have this baby today.' And I'm just like: 'Shut up, go away. You're not helping.'"
By the time she arrived at the hospital — where she had a 'lovely midwife' all to herself because there was no one else on the ward — she said: "Dr Hilary, had kept me so calm. And I think that was the right way to be.
"I remember going: 'Okay, fine. It's coming today.' I don't even know why I was not fazed or fussed by it.
"But I had Debbie Dresses by my side and then just call my husband and said: 'Oh, you need to come, bring an overnight bag and then when he walked in the room I was like: 'Baby's coming today!'"
The presenter, who joined ITV in 2012, said her science background was helpful when she was in the hospital, but also that 'it was a bit annoying for some of the doctors'.
She and her husband, who met when they were both doing a physics degree, often had more scientific explanations from the doctors, but also questioned the doctors when they felt they needed to.
Tobin said: "It also meant that sometimes we would really question them. And obviously they're doctors and they know their stuff. But we would say: 'Right, you're thinking this, but actually could it be this? Or could it be that?'
"And luckily, we have someone in the family who knows quite a lot about this sort of stuff as well. So we just kept putting, different scenarios forward."
WATCH: Laura Tobin on climate change, being competitive and getting her daughter interested in science