Ashley Graham thought she was suffering pre-natal depression during her pregnancy.

The 32-year-old model - who gave birth to her son Isaac on January 18 - experienced dramatic mood swings during her pregnancy, but she's subsequently realised it was ''normal''.

Recalling her first pregnancy experience, Ashley said: ''I was so excited. I knew immediately I was going to be a great mom.

''That was the wildest part. I thought, 'What about the things I've told myself? What about the affirmations I've gone through?' None of these mattered because my body was changing so rapidly. It really took me some time to figure it out mentally, because it was like there was an alien taking over my body.''

At the time, Ashley thought she had pre-natal depression - but she now believes that wasn't the case.

She told Harper's Bazaar UK magazine: ''When you go from laughing to crying in 30 seconds, you do wonder if you are OK. Unbeknown to me, that's pregnancy.

''One of the best things I did for myself was to make pregnant friends, and then I realised I wasn't alone, I was normal, and that calmed me down. I started to enjoy being pregnant in my third trimester.''

Ashley gave birth at her home in Brooklyn, New York.

And her husband Justin Ervin was a helpless - and emotional - onlooker as they welcomed their first child into the world.

The brunette beauty recalled: ''Justin wanted to be as helpful as possible, and the midwife told him: there's nothing you can do, nothing.

''There's a photo of him rubbing my arm as I'm hanging over the edge of the pool, gazing into the eyes of the midwife, who's keeping me focused and helping me count.

''You can tell there's a tear running down his face - it was agonising for him to see me in so much pain and not to be able to do anything about it.

''I was in the pool, and I looked over to see him in the kitchen cutting up meat and adding seasoning, because it was all he could do ...''