And just to add, gummy vitamins shouldn't be taken by anyone for anything. It's just candy. There are always better supplements than gummy anything. But the above is correct about all supplements -- taking too much is taking too much. Whether it can cause stillbirth is probably unlikely but probably also unknown.
Taking too much of them can cause serious side effects and problems for you and your baby. According to the Dartmouth-Hitchcock Norris Cotton Cancer Center.