Lorna Fulton, 44, was size 24 and was trying for a baby when doctors advised her to lose weight if she wanted to conceive naturally.
So the Glaswegian went on a diet and soon lost two stone. But then she was baffled when she started to put on weight again and she went up to 19st.
She was referred to specialists, who discovered a huge and deadly ovarian cyst.
She said: "I joined a diet class and started eating a healthier and within a few months I'd lost two stone.
"I went out to buy a new outfit to celebrate. I had been a size 24 so I picked up a size 22, hoping it would now fit comfortably - but I couldn't get into it as around my middle was too big and I had to go up to a size 26.
"It was so noticeable that people at work thought I was pregnant and kept asking when I was due. So I went to see my GP, who was convinced at first I was pregnant. But when a pregnancy test proved negative I knew there was something more sinister lurking.
"I was referred to hospital where I had a biopsy, a CT scan and an ultrasound. Finally a specialist told me that I had a huge ovarian cyst, which from the scan they could see was filled with fluid.
"They told me if I didn't have it removed I could die."
Lorna had a full hysterectomy at Glasgow's Royal Infirmary during which doctors drained over 32 litres of fluid from her stomach.
She said: "The doctors said it was too risky to remove it whole so it had to be drained. Plus there was a chance it could come back in my other ovary. I had to have my operation in the maternity unit. It was horrible.
"I was really sad, but I knew I just had to deal with the fact I wouldn't be having children. I knew what was involved in the operation, but I just wanted it gone.
"I went under the knife and said goodbye to having children once and for all. Waking up from the op, I felt much better and the following day weighed myself.
"At that point I'd been 19 stone and after having the lump removed I was now down to 14. It was unbelievable I'd been carrying around all that weight.
"I've now accepted that children are not on the cards for me. But things could have been so much worse. I'm lucky to be alive."
The NHS advises that ovarian cysts, fluid-filled sacs that develops on ovaries, are common but usually harmless and disappear without the need for treatment. They only cause symptoms if they rupture, are larger than normal or block blood supply to the ovaries.