I do not have any experience with yellows, but I have fed gravid greens very small meals (~ 25% of normal) on a once per month basis. They will usually fed over roughly the first half or two-thirds of the gestation period. They will usually refuse after that, but I would not recommend trying to feed them later than this in the gestation period anyway. I think this probably does help them somewhat with the drain on their reserves. I believe the standard gestation for yellows is about 5 or 6 months, and there are some yellow breeders here that could give you more accurate figures from personal experience.
Kelly