My sister told me she started taking Prenatal pills before she got pregnant to help her get pregnant and ended up pregnant with my niece. Has anyone else heard of this? If so please comment. Do you think it work?

Back story: I've been TTC since January of 2014 after getting off the mirena after 5 years and haven't been able to get pregnant. Before getting it put in I was able to get pregnant within a snap lol my son and my daughter are 10 months apart which made me decide to get the Mirena. Now I'm ready for another baby and haven been so lucky. So with that being said any advice is greatly appreciated.