If my husband smoked marijuana regularly for 20 years and during the time we conceived, could this have caused our blighted ovum?

Depends.: No but if he smoked around you and you inhaled the same smoke, this might have some effect. There are no studies i know of that marijuana causes blighted ovum.

No proven link : Blighted ovum is common- about 20% of pregnancies end in miscarriage ; about half are due to blighted ovums, due to chromosomal abnormalities. Some research purported to find marijuana causes chromosomal abnormalities in sperm but that research doesn't hold up to scrutiny- see the teratogenicity section of this review: http://bit.Ly/gfpwqb most with blighted ovums have normal future pregnancies.

No: Smoking marijuana shouldn't have caused a blighted ovum.