Can prenatal vitamins lessen your chance of miscarriage?

No: No evidence to support this.

Probably but...: Prenatal vits have Folic Acid which significantly reduces risk of neural tube defects so one would expect they reduce miscarriage. A 2009 study confirmed this- see http://miscarriage.about.com/b/2009/05/25/could-prenatal-vitamins-reduce-risk-of-miscarriage.htm However, a recent study in Denmark suggests taking prenatal vits before pregnancy increased risk. This makes no sense.More research needed.

Only if: you are deficient in vitamin B12 and folate (folic acid)