The 'Shake It Off' hitmaker – who welcomed the twins with husband Nick Cannon six months ago – has managed to lose significant weight, but admits she was worried she would never be the same again following the pregnancy.
Mariah – who embarked on the Jenny Craig diet plan to shed her excess pounds - said: "In the beginning, when I first had the babies, I had so much edema, water and swelling. Most pregnant women have that just in their feet.
"One day I was doing my thank-yous and I noticed it started rising up the leg, so I had edema. I didn't think I would ever be the same person.
"The first week, I lost 40 lbs of just water. It was just water, initially. When I started with the programme, I lost at least 30 lbs of weight that needs to be lost."
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The 42-year-old star struggled throughout her pregnancy and even had trouble when she was confined to her bed.
Speaking on 'The Rosie Show', she explained: "I had a really tough pregnancy. I was supposed to be on bed rest, but it was so bad then even bed hurt. I learned a lot being pregnant, watching my body change."
Mariah felt particularly "vulnerable" while carrying her children, and is delighted to have her old body back.
She added: "The whole point of this is not just like, 'Oh hey, look at me and my weight loss, I'm fantastic.' It’s really healthy. Like I said, I learned it when I became helpless and felt so vulnerable like never before in my life."