Amag Pharmaceuticals Inc., of Waltham, Mass., announced the pricing of an upsized underwritten public offering of $300 million worth of convertible senior notes, due 2022. The original offering sought to raise $250 million. J.P. Morgan Securities LLC and Morgan Stanley & Co. LLC are acting as book-running managers. Amag has granted them the option to purchase up to an additional $45 million principal amount of notes solely to cover overallotments. The offering is expected to close on May 10.