An attorney for more than 1,200 women who say they were injured by the Mirena intrauterine device argued before a federal appeals court on Monday that their lawsuit should be revived based on Bayer's own admissions that its device can perforate the uterus.

But the attorney for Bayer, which successfully argued for summary judgment last year after U.S. District Judge Cathy Seibel of the Southern District of New York disqualified all three of the plaintiffs' causation experts, said the admissions, contained in internal emails, do not meet the burden of proof for causation.

Mirena delivers a hormone called levonorgestrel that prevents pregnancy for up to five years; labels on Mirena warn that perforation of the uterus can occur when the device is inserted.