Lighter and 35. Eighteen stone is a lot, regardless of height, unless you're a seriously muscular athlete. I've just had my first baby at almost 41 and 3 stone overweight. I was active beforehand, I cycled 18 miles a day, swam regularly, and walked a lot, but I really love food.
Fortunately, my pregnancy was straightforward, bar a touch of diabetes right at the end. But I was very lucky, and my active lifestyle probably helped. It would've been even easier if I'd been a healthier weight beforehand.
Pregnancy puts a huge strain in your body, and getting in shape afterwards is difficult due to the demands of having a small baby.
I watched what I ate whilst pregnant and was back to my pre-pregnancy weight 3 weeks after birth, but I still have those three stone to lose before I try to get pregnant again.
Get into good habits now and it will help you bounce back, but also it will help you model a healthier lifestyle for your child.
If you diet, toxins are freed in the body. So if you diet when pregnant, those toxins will affect the baby.
By the way, the above is utter, utter, bollocks.