Pfizer Inc scored a key victory Friday when it was cleared of liability in the first U.S. trial involving claims that its antidepressant Zoloft can cause birth defects in children born to women who take the drug while pregnant. Plaintiff Kristyn Pesante claimed that Pfizer failed to warn that using Zoloft during pregnancy could cause birth defects and sought damages after her son was born with a rare, serious congenital heart problem.