The oversight angered would-be mothers, many of whom didn't find out about the April 22 incident until they made appointments with their doctors to have embryos implanted.
An official at La Paz Hospital in Madrid told ThinkSpain the freezer's nitrogen levels are checked twice a week to ensure it's cold enough to keep the embryos frozen. Records show the freezer had last been checked five days before the leak was discovered.
ThinkSpain said only 70 of the women whose embryos were lost have been notified.
La Paz has offered to allow the women to go through the egg harvesting process again free of charge, though some said they'd prefer other options. Egg harvesting requires an in-patient stay and a procedure done under general anesthetic.