(CNN) An Ohio fertility clinic says more than 4,000 eggs and embryos were affected by a freezer malfunction, double the number previously thought -- and that it's unlikely any of them are viable.

The University Hospitals Fertility Clinic also said about 950 families were affected by the storage tank failure earlier this month . At the time, the facility in Cleveland said it believed about 700 families were affected.

In a letter sent to the families, dated Monday and obtained by CNN on Tuesday, University Hospitals said it was sharing the updated information with a "heavy heart."

"The technical manner in which the eggs and embryos are stored in these freezers complicated our initial determination of how many patients and specimens were affected," the letter stated.

At the time of the failure, the clinic said it was unable to determine right away whether any of the eggs and embryos were still viable. In the letter this week, it said, "We are heartbroken to tell you that it's unlikely any are viable."

Read More