Eating potatoes or chips on most days of the week may increase a woman's risk of diabetes during pregnancy, say US researchers.
This is probably because starch in spuds can trigger a sharp rise in blood sugar levels, they say.
Their study in the BMJ tracked more than 21,000 pregnancies.
But UK experts say proof is lacking and lots of people need to eat more starchy foods for fibre, as well as fresh fruit and veg.
The BMJ study linked high potato consumption to a higher diabetes risk.
Swapping a couple of servings a week for other vegetables should counter this, say the authors.
UK dietary advice says starchy foods (carbohydrates) such as potatoes should make up about a third of the food people eat.
There is no official limit on how much carbohydrate people should consume each week.