I just heard basil seeds could cause contractions, is it possible that a vietnamese dessert made with tons of basil seeds could cause miscarriage?

Basil seeds: Using basil as a spice is safe in pregnancy. An essential oil is sometimes made from the leaves and seeds -- and this contains a high concentration of the constituent estragole. Estragole can cause uterine contractions, thus may not be safe in pregnancy unless you're already in labor. The essential oil probably uses a lot more of these seeds than you ate in your dessert. If concerned, see ob.