Is there any difference between osmotic fragility of fetal red blood cells and adult red blood cells?

Yes.: Fetal red cells are larger, and with extra surface area to volume and therefore a bit more resistant to osmotic injury than adult red cells.

Osmotic fragility: Osmotic fragility testing is commonly used to screen for hereditary spherocytosis (hs). This test can give a false negative if testing in newborns (that is, you can have hs as a newborn and the test comes back saying you don't). There are new tests using facs (fluorescence activated cell sorting) analysis that can diagnose hs in a newborn.