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Factors to Consider When Interpreting IVF Success Rates

Daniel E. Stein, MD, Co-Director and IVF Medical Director
Continuum Reproductive Center, New York City

Many couples in need of fertility care are fortunate to have several practices to choose from. Information about different fertility centers is typically obtained from referring physicians, friends, family members, co-workers, and the internet. Some information can be very helpful; however, pregnancy and birth rates from IVF procedures are subject to influences that may vary from clinic to clinic, making success-rate comparisons between clinics problematic for consumers. These issues are outlined in this article and include: physician criteria for recommending IVF; age of patients; physician policy concerning prior failed IVF; policy regarding ovarian reserve markers; cycle-cancellation policies; number of embryos transferred; and economic factors. In most cases, these differences reflect the philosophies and clinical practices of the physicians, not sinister or purposely deceptive manipulations. Nonetheless, consumers need to be aware of these differences when comparing success rates, and also, put success rates in perspective when choosing a clinic. Even the Society for Assisted Reproductive Technologies, the organization to which IVF practices report their pregnancy rates, cautions consumers that IVF success rate data should “not be used for comparing clinics.”

Instead, consumers should choose a center with board-certified or board-eligible reproductive endocrinologists and several years of experience in the evaluation and treatment of a variety of fertility and reproductive hormonal disorders. Consumers should look at how a program has performed over several years rather than in one particular year. Patients and couples should speak with their obstetrician-gynecologists about their experiences with various programs. Consumers who choose a program simply by its name or reported success rates might be disappointed with their choice.

Centers with IVF programs are required by law to report statistical information to the Centers for Disease Control (CDC). Most reputable practices are also members of the Society for Assisted Reproduction (SART) to which they submit annual statistical data regarding IVF cycles performed at that center. Data published by the CDC and SART generally represent pregnancy rates from two years earlier; therefore, the clinic’s performance may have changed.

IVF success rates are expressed in a number of ways. Programs report the number of IVF cycles initiated as well as the number of cycles cancelled in a given year. Practices also report the number of single and multiple pregnancies that occurred and the number of pregnancies that achieved a live birth (i.e. those not lost to early and late miscarriages). Pregnancy rates are expressed using different denominators (e.g. pregnancies per cycle initiated, pregnancies per egg retrieval or per embryo transfer). The number of embryos transferred per case is reported as well. Data from fresh cycles using a woman’s own eggs, cycles using a donor’s eggs, and cycles using frozen embryos are all reported. All of these statistics can be subject to bias.

While IVF success rates might indeed reflect the skill and technical abilities of the center involved, they also reflect the ways by which patients are selected to participate in the IVF program.

Physician criteria for recommending IVF

One essential factor frequently omitted from discussions on IVF success rates is how a patient or couple ever came to do IVF in the first place.  Infertility and sub-fertility are caused by a host of factors including sperm and/or egg abnormalities, ovulation disorders, pelvic disease, fallopian tube abnormalities and unexplained factors. While IVF is appropriate for many infertile couples, it is often unnecessary for others. Oral and injectable medications, lifestyle changes, intrauterine inseminations and operative procedures help many infertile patients achieve success effectively and safely. While most fertility practices are responsible and honorable in their recommendations to patients, others might urge patients to enter the IVF arena prematurely. The pool of patients who do not require IVF is often inherently more fertile (and thus more likely to conceive) than the pool that does ultimately need IVF.  Some centers include in their IVF pool many patients who might very well conceive with less invasive techniques; such programs are likely to enhance their overall success rates without actually being “better” centers. As an extreme example, if Program A enters all patients into IVF before treating its patients with more conservative measures, and Program B recruits patients into IVF only after these patients have failed to conceive with multiple cycles of ovarian stimulation and insemination, Program A is likely to post higher IVF success rate than Program B.  The most fertile patients in Program B might have become pregnant with more conservative treatments leaving only the most challenging and difficult-to-conceive patients in the IVF group. The quality of the physicians and laboratory team from Program B might be comparable or even superior to those of Program A despite lower reported pregnancy rates.

Age of patients

As IVF success rates diminish markedly with age, analyzing statistics by the age of the woman has helped to reduce the statistical advantage some programs had in the past by selecting only young patients for IVF. Classification by age, however, does not completely abolish age-bias. For example, in the 38-40 age group (one of the arbitrary age classifications used by SART), 80% of the patients in Program A might be 38 years of age, 10% age 39  and 10% age 40. Program B might have 10% patients at age 38, 10% age 39 and 80% age 40. The IVF consumer does not have this information and therefore might unjustifiably think more favorably of Program A than Program B.

Physician policy concerning prior failed IVF

A well-established prognostic factor for a couple’s chances to succeed in IVF is its experience in a prior ovarian stimulation or IVF cycle. Some women who have failed to conceive in a prior cycle, or who have had a poor response to stimulation medications in the past, are advised to undergo egg donation. This advice is appropriate in many but not necessarily all cases. If a couple declines egg donation and desires to attempt another IVF cycle despite low chances of success, some programs will allow the couple to undergo additional IVF cycles using the woman’s own eggs. Other programs are less flexible and refuse to consider any treatments other than egg donation. Again, as an extreme example, if Program A includes few or no patients with a history of prior failed cycles or a prior poor response to medications, and Program B is willing to make one or more attempts for success in poor-prognosis patients, Program A is likely to report markedly higher pregnancy rates than Program B, regardless of the quality of the program.

Policy regarding ovarian reserve markers

Reproductive endocrinologists try earnestly to predict which patients or couples have a good chance for success with IVF and which do not. Ovarian reserve markers are blood tests or ultrasound characteristics used to predict if a woman will produce a sufficient number of high-quality eggs in an IVF cycle.  Reproductive specialists use the results of these tests to counsel patients regarding their chances of success and to help select a medication protocol for that patient. Some of the markers familiar to patients include Follicle Stimulating Hormone (FSH) levels, Antimullerian Hormone (AMH) levels, Antral Follicle Counts, Inhibin B levels and others. None of these markers are absolute predictors of the chances of pregnancy in a given IVF cycle. Some practices are very strict in their criteria for inclusion in their IVF program and set arbitrary “cut-off” values for some of the ovarian reserve markers – in some of these programs a patient will not be allowed to participate in IVF using their own eggs. Such patients are given the option of using donated eggs. Other programs, however, are far more liberal in their cut-off values or set no arbitrary cut-off values at all. Such programs are far more likely to allow patients with less-than-optimal ovarian reserve markers (and thus lower chances of success) to undergo one or more fresh IVF cycles. If Program A utilizes very strict criteria and Program B does not, Program A will likely report higher pregnancy rates than Program B, again in no way accurately reflecting the quality of the medical and laboratory team in either program.

Cycle-cancellation policies

During an IVF cycle, physicians monitor the response of the patient to ovarian stimulation medications. In the event that a patient produces very few follicles the physician might cancel (i.e. discontinue) that cycle. The physician might believe that to cancel such a cycle is in the best interests of the patient, perhaps allowing the patient to initiate a new cycle with a different stimulation protocol. The physician might also be concerned that the chance of pregnancy will be greatly diminished in such a cycle and have a negative impact on the program’s success rates. If, for example, Program A cancels cycles in which there appear to be three or less developing follicles, and Program B allows patients with at least one follicle to go to egg retrieval, Program B will naturally assume more risk than Program A for obtaining few or no healthy eggs.  As such, Program B might have lower pregnancy rates despite being an excellent quality program.

Number of embryos transferred

Over the past decade, reproductive endocrinologists have made a significant effort to reduce the incidence of multiple gestations (twin, triplets or more). Such pregnancies are associated with a higher rate of premature births, cesarean sections, obstetrical hemorrhage, and maternal disorders such as gestational diabetes and pregnancy-induced hypertension.  The primary means to reduce multiple gestations is by reducing the number of embryos transferred to the uterus. The American Society for Reproductive Medicine publishes guidelines for the number of embryos to transfer based on a woman’s age, the stage of embryo development, and whether or not the patient has extra embryos to freeze. Some centers encourage appropriate candidates to consider elective single embryo transfers even if this practice might compromise pregnancy rates for some couples. One program might increase its success rates by transferring a higher number of embryos to a patient than another program might do. If Program A routinely transfers three high-quality embryos to women between ages 35-37, and Program B transfers only two high-quality embryos in such cases, it is likely that Program A will report slightly higher pregnancy rates despite placing its patients at a greater risk of multiple gestations.

Economic factors

Practices in different communities or even different neighborhoods often have patients or couples of dissimilar economic means. Patients that require insurance coverage in order to do IVF are subject to the restrictions placed upon them by their insurer. For example, some insurers require patients to undergo a certain number of non-IVF cycles before proceeding with IVF. The most fertile patients might become pregnant with less invasive methods. As such, the pool of patients who end up requiring IVF might be less fertile (with a poorer prognosis) in insurance-dominant, less-affluent practices than in practices in more affluent communities, those in which patients and couples can afford to proceed with IVF without insurance funding.

These are some of the principle issues that make it hard to compare IVF pregnancy and birth rates between clinics. Again, when comparing success rates, consumers need to be aware that these differences may exist. When reviewing the fertility centers available, consumers are likely to make more effective choices if they consider several factors, such as the reproductive endocrinologist’s board certification and other qualifications; the center’s number of years experience in the evaluation and treatment of a variety of fertility and reproductive hormonal disorders, and the recommendations of trusted physicians.

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