Hi clemenceko,
SBD-22 the mother got morning sickness and she run into the restroom (after having sex with her son - cum inside)
SBD-26 the mother touched her belly when taking bath; in other scene, she and her son touching her belly (at the end of the movie)
SBD-33 the mother got morning sickness when she and her son start making love (at the end of the movie)
SBD-44 the mother fondles her belly and show her son that she got pregnant by him (at the end of the movie)
All of the 4 SBD movies that I already posted were considered as incest movies with content (drama), so I think they are better than other movies without content.
Cheers