At a conference of perinatalogist attended by
my perinatalogist, he said that most cases of extreme sizes in gestational
sac, whether too small or too large for the gestational age, the fetus has a weak heartrate (which mine did not) and will end in miscarriage. There is no known cause for the sac sizes that they have been able to pinpoint as of yet.
Again, if I find out anything that may be useful at my appointment tomorrow I will be sure to pass it along.