Data Murky on Fertility Rates

Here’s the question on the minds of people who spend tens of thousands of dollars on fertility treatments: What are my chances of having a healthy baby?

As it turns out, it’s not always easy to tell.

Since 1992, clinics have been required to report their success rates, defined as the number of live births per in vitro fertilization cycle, to the Centers for Disease Control and Prevention. They are also supposed to report how many cycles they perform and whether the cycles involve the woman’s own eggs or donor eggs, among other factors.

But there is little regulatory enforcement of these requirements by either the C.D.C. or the Society for Assisted Reproductive Technologies, the association that forwards this data to the agency. Roughly 10 percent of clinics do not report at all.

This is a multibillion-dollar industry, and there is financial pressure for clinics to claim frequent success. “Clinics are competing with each other based on pregnancy and live birthrates,” said Dr. Vitaly Kushnir, a reproductive endocrinologist in New York who researches success rates. The clinics do not want...