Marvel Studies has released several superhero films in the past six years. None has had a female lead character, with Scarlett Johansson's Black Widow coming closest.

Black Widow has been in a number of superhero movies. She first appeared in "Iron Man 2" as a S.H.I.E.L.D. agent sent by Nick Fury to keep an eye on lead character Tony Stark, played by Robert Downey Jr. In "The Avengers," she got her own story arc. She next appeared in "Captain America: The Winter Soldier." The latest in the Marvel superheroes series is "The Avengers: Age of Ultron," in which Black Widow is said to have a big part.

There might be a catch: Scarlett Johansson is pregnant. She and fiancé Romain Dauriac are expecting their first child, leaving fans to wonder whether her pregnancy will affect the shooting of the second Avengers movie.

Her pregnancy is affecting production of "The Avengers: Age of Ultron," but Marvel is reportedly working around things by fast-tracking her scenes. With the production team's penchant for going back to where it left off or showing scenes that had been skipped over, movie-goers can expect to see flashbacks to scenes from the previous film.

According to director Joss Whedon, the filming schedule and script have not changed. In April, when Johansson started shooting, she was four or five months pregnant but still not showing much. There was still the question of stunt work -- a major part of the Black Widow. While many filming tactics could help hide the pregnancy, getting her into that tight leather suit must have been more difficult.

"The Avengers: Age of Ultron" hits theaters May 1, 2015. James Spader will play the villain Ultron, and new characters to be introduced include Elizabeth Olsen (Scarlet Witch), Aaron Taylor-Johnson (Quicksilver), Paul Bettany (The Vision), Don Cheadle (Colonel James Rhodes / War Machine) and Thomas Kretschmann (Baron Wolfgang von Strucker).