After a disappointing end to a nine-year trial, the U.S. Food and Drug Administration officially gave AMAG Pharmaceuticals notice of the proposal to withdraw approval of Makena, an injectable progestin treatment to reduce preterm births.  

The U.S. Food and Drug Administration approved South African drugmaker Aspen Pharmacare’s hydroxyprogesterone caproate (HPC), which is used to prevent preterm birth in pregnant women.

Shares of AMAG Pharmaceuticals plunged after the company’s Phase III PROLONG trial of Makena failed to show a statistically significant difference from placebo in preventing preterm births.