Understanding IVF Success Rates

One of the most frequently asked initial questions to our office is, “What are your success rates?” Knowing a center’s success rate can be quite useful in assisting prospective patients narrow down a center for them; however, it is important to know what posted success rates actually means. Each year, the Centers for Disease Control and Prevention (CDC) compiles and publishes data regarding individual assisted reproductive technology (ART) centers statistics; however, it should be noted that the annual reports are from a period of time two years previous. ART centers are mandated to report their rates to the CDC but some also choose to report statistics to the Society for Assisted Reproductive Technologies (SART).

The CDC does provide some cautionary advice when reviewing and comparing success rates. The following is this cautionary advice and a sample clinic table.

Many people considering ART will want to use this report to find the “best” clinic. However, comparisons between clinics must be made with caution. Many factors contribute to the success of an ART procedure. Some factors are related to the training and experience of the ART clinic and laboratory professionals and the quality of services they provide. Other factors are related to the patients themselves, such as their age, quality of their eggs and sperm, cause of their infertility, genetic factors, and diagnosis. Some clinics may be more willing than others to accept patients with low chances of success or may specialize in ART treatments that attract particular types of patients.

We encourage consumers considering ART to contact clinics to discuss their specific medical situations and their potential for success using ART. Because clinics did not have the opportunity to provide narratives to explain their data in this report, such conversations could provide additional information to help consumers decide whether to use ART

Success Rates May Vary

A clinic’s success rates may vary from year to year even if all determining factors remain the same. The more cycles that a clinic carries out, the less the rate is likely to vary. Conversely, clinics that perform fewer cycles are likely to have more variability in success rates from year to year. As an extreme example, if a clinic reports only one ART cycle in a given category, as is sometimes the case in the data presented here, the clinic’s success rate in that category would be either 0% or 100%. Because success rates may be misleading if they are based on a small number, the rates are shown as fractions rather than percentages when fewer than 20 cycles or outcomes (pregnancies, transfers, births) are reported in a given category.

Some clinics see more than the average number of patients with difficult infertility problems

Some clinics are willing to offer ART to most potential patients, even those who have a low probability of success. Others discourage such patients or encourage them to use donor eggs, a practice that results in higher success rates among older women. Clinics that accept a higher percentage of women who previously have had multiple unsuccessful ART cycles will generally have lower success rates. In contrast, clinics that offer ART procedures to women who might have become pregnant with less technologically advanced treatment will generally have higher success rates.

The percentage of cycles that are canceled varies

Percentages of canceled cycles using fresh nondonor eggs or embryos vary among clinics from less than 1% to, in a few cases, more than 25%. A high percentage of cancellations tends to lower the percentage of cycles resulting in live births but may increase the percentage of embryo transfers resulting in live births.

Percentages of unstimulated (or “natural”) cycles are included with those for stimulated cycles

In an unstimulated cycle, the woman ovulates naturally rather than as the result of the daily injections used in stimulated cycles. Unstimulated cycles are less expensive because they require no daily injections and fewer ultrasounds and blood tests. However, women who use natural or mild stimulation produce only one or two follicles, thus reducing the potential number of embryos for transfer. As a result, clinics that perform a relatively high percentage of unstimulated cycles may have lower success rates. Nationally, 1% of ART cycles using fresh nondonor eggs or embryos in 2012 were unstimulated.

Success rates are calculated per cycle rather than per patient

Success rates shown in this report are presented in terms of cycles, as required by law, rather than in terms of patients. As a result, patients who had more than one ART cycle in a year are represented in multiple cycles that are not linked. In addition, for patients who undergo both fresh and frozen cycles, success rates are calculated separately for each cycle. Clinics that have a very high percentage of cycles resulting in live births with frozen embryos would have higher ART success rates if these births were included as successes from the original stimulated cycle. Consumers should look at both rates (for cycles using fresh embryos and for those using frozen embryos) when assessing a clinic’s success rates.

The number of embryos transferred varies from clinic to clinic

In 2012, the average number of embryos that nearly all clinics transferred to women younger than age 35 ranged from 1 to 3 for fresh nondonor cycles. The American Society for Reproductive Medicine (ASRM) and the Society for Assisted Reproductive Technology (SART) discourage the transfer of a large number of embryos because of the increased likelihood of multiple-fetus pregnancies. Multiple-fetus pregnancies, in turn, increase the probability of premature births and related health problems.