When Black Widow and Hulk are figuring out the status and future of their relationship in Avengers: Age Of Ultron, the former dropped a rather significant bombshell: she is incapable of having children.
This may not be something that specifically comes up in the Black Widow solo film, but it’s a standout detail that could wind up informing elements of the character – such as her relationship with her spy “family” who we’ll meet in the movie.
It’s a horrible part of her story that extends from her time in the Red Room, as it was believed by her Russian handlers that becoming pregnant would be a distraction from her life as a killer, so the option was surgically taken away from her.