No - I started my diet at 28 weeks.
Mornings would be porridge, or granary bread dipped in egg, fried. Fruit juice - just one glass a day, with breakfast. I ended up eating the same thing every day to make life easier.
Midmorning I'd have a handful of nuts plus a yogurt drink or glass of milk.
Lunch would be vegetable soups, oily fish on granary toast, or baked beans with grated cheese and other veg on the side. Lots of salads with avocados.
Dinner would be any protein foods (eggs, fish, meat) , plus veg in some form. Only very small amounts of potatoes. If rice then it would be a small amount of basmati or wild rice. If I had pasta I had it as a small side dish. Also tried to have wholemeal pasta. One piece of fruit for pudding, but no fruit between meals. No other restrictions on quantities, except on potatoes, pasta and rice, which should only be two or three tablespoonsful, not the basis of a whole meal. I also ate loads of curry made with pulses.
Sounds really boring doesn't it? Oh god, it was. I felt very restricted. Didn't like not being able to each much fruit.
I also supplemented with cinnamon, which is known to reduce blood sugars. I took about a gram a day. It's not recommended for pregancy - in first trimester it's rumoured to be linked to miscarriage, but I felt there was very scant evidence of harm in third trimester and felt it was more important to keep weight of baby down to avoid serious birth injuries.
On the plus side - I lost so much weight on this diet that within 2 weeks of the birth I was able to get into a size 10 pair of trousers. And my little boy is very very robust and healthy. He had the lowest birthweight but is the biggest of the three children in height. He's a very muscly and lean child. Bright too!