The road to victory for plaintiffs alleging that Pfizer’s antidepressant Zoloft causes birth defects has gotten steeper since a federal judge barred the testimony of one of their key expert witnesses.

After a week of Daubert hearings in April, U.S. District Judge Cynthia Rufe of the Eastern District of Pennsylvania ruled this week that Dr. Anick Bérard’s testimony would be excluded from trial.