Its not clear how much screen time she would have had, but its clear that the original Mutants are the first to go when it comes to X-Men: Days of Future Past, with director Bryan Singer focusing more on the X-Men: First Class cast in telling this story.
An onset source revealed the news to New York Daily, saying:
Halle Berry learned of her pregnancy just as shooting started on X-Men: Days of Future Past, which saw her role being cut down considerably. The actress herself revealed that there would be limitations to her performance.
The actress had gone onto tease that fans would learn something new and shocking about Storm X-Men: Days of Future Past., but now we'll have to wait for the Blu-ray to see these deleted scenes, to know what this secret is. Bryan Singer has promised that we will be seeing quite a lot of cut footage when the movie finishes its theatrical run and heads for home entertainment venues.
X-Men: Days of Future Past was released May 23rd, 2014 and stars Hugh Jackman, James McAvoy, Michael Fassbender, Jennifer Lawrence, Halle Berry, Nicholas Hoult, Anna Paquin, Ellen Page. The film is directed by Bryan Singer.