If you use a eGFP/WT female crossed to a WT/WT male, half of the pups should be WT/WT. In those embryos any GFP expressing cells will have a presumably maternal origin.

John Hardy Lockhart thank you for your answer! I am already using this methodology to obtain the contrast between maternal cells in the embryo's brain. But, sometimes there are pregnancies where the majority of embryos is eGFP. In that case, I was looking for a way to use the eGFP embryos through immunohistochemistry instead of wasting all this rich biological material. I appreciate your attention!