A decidual cast is rare, and there's nothing you can do to prevent it. A decidual cast is a possible side effect for some contraceptives. You should be aware of the side effects of any hormonal contraceptives you use.

Why did I have a decidual cast?

2 Decidual cast formation can be associated with ectopic pregnancy or, less commonly, exogenous progesterone. Decidual casts have been attributed to use of oral contraceptives, injectable progesterone, or an implantable progesterone delivery system (Nexplanon).

Are decidual casts bad?

A decidual cast isn't a signal of a serious condition. There's no record of long-term negative side effects, and there's also very little risk that you'll have another one.