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"What's Your Success Rate?": Understanding IVF Pregnancy Statistics: Part II

Joseph D. Schulman, MD


"The laws of probability, so true in general, so fallacious in particular."
Edward Gibbon

"I'm from the government, and I'm here to help."
Anonymous humorist

This article is intended to be read as a supplement to the main "What's Your Success Rate?" discussion which has been present on our Web site for some time, and which has attracted much favorable comment from patients, statisticians, and infertility experts. In fact, it has been primarily through information from these sources that we have become aware of a number of additional means by which "success rate" data can be manipulated to improve the appearance, but not the substance, of what is offered to the public. Some of these are described below. As in the prior analysis, we here demonstrate only a few of the methods used in some infertility treatment centers for achieving "good looking" statistics. And we again remind our readers that the primary theme behind making infertility therapy statistics look good is not to corrupt the mathematical computation but to select the patients and cycles, and hence the data, going into those calculations.

1. Classify difficult patients as research subjects: Certain IVF centers enhance their statistics dramatically by the simple expedient of classifying their most difficult patients as "research patients", and then failing to include them as part of their "real" clinical statistics. This allows such facilities, of course, to maintain their volume of activity, and do the same type of research that is appropriately done at many IVF facilities, while looking better than their peers. Within any group, or age group cluster, of patients there are very wide variations in the likelihood of pregnancy for individuals. The systematic exclusion of the most challenging patients from the clinical statistics enriches the success rate of the reported subset automatically.

2. Move challenging patients to donor egg services early: There can be no question that donor egg substitution in circumstances where the woman's ovaries show some aging effects or where egg quality appears to be somewhat reduced can be very effective in achieving pregnancy. But at what point should individual patients should be encouraged to consider the alternative of donor egg? Any IVF center that directs candidate patients at a relatively early stage toward the donor egg process, especially if this is reinforced by refusing to further provide conventional IVF services to such women, will be assured of achieving "better" statistics.

3. Discourage embryo cryopreservation: This is powerful, yet subtle. A patient goes through an IVF cycle, produces let us say 6 to 9 embryos, and is advised that her "embryos do not look good enough to freeze". This forecloses the conventional decision to transfer approximately 3 embryos, and cryopreserve the remainder to be used in one or more frozen embryo transfer cycles if the initial embryo transfer is unsuccessful. Consider what happens when freezing is precluded. First, there will usually be a larger number of embryos transferred than would otherwise have been preferred by the couple - and the "success rate" statistics of the IVF facility will thereby be enhanced. But the statistics will be further improved for an additional, more complex reason. Patients vary in the ease with which embryos will implant in their uterus and produce a pregnancy. A patient may be perfectly normal from this perspective, yet fail to become pregnant with her first fresh embryo transfer. There is a substantial probability that such a "good" patient will then conceive on her subsequent frozen transfer cycle(s). If she does so, she is a statistical failure for "success rate" purposes, since this is calculated from non-cryopreserved cycles, and she will not medically reappear for a second fresh IVF cycle. But if freezing is not done, and if a pregnancy does not result from the first fresh embryo transfer, such patients will likely do second full IVF cycles. And many of them will then become pregnant on this second fresh cycle. Thus, the discouragement of freezing leads to a group of patients doing repeat fresh IVF cycles which is predictably enriched for better patients compared to what would happen if embryo freezing had been more broadly utilized. The result is, automatically, "better" statistics in the aggregated fresh cycles. And it need not perhaps be added that such an approach enhances the economic benefit to the IVF center by substituting a full IVF cycle for a much less costly frozen transfer cycle.

4. Attract better patients with a "refund package": Refund or "Pregnancy Guarantee™" packages offer enhanced up-front fees for IVF to selected qualifying patients who receive a rebate if a pregnancy is not attained. Qualifying patients necessarily includes only more favorable patients, and excludes those representing more difficult medical challenges. From a statistics perspective this type of program ensures an enrichment in favorable patients and leads almost automatically to "better" success rates. IVF centers which have a substantial fraction of their patients involved in refund programs are virtually guaranteed to manifest higher average "success rates" than those with fewer such patients or which do not offer refund programs at all.  This apparent improvement in "success rates" when refund programs are prominent is, of course, attained without producing a true improvement in the quality of care provided to anyone.

In concluding this supplement, we would like to express our respect for the integrity of those many physicians in the IVF field who have resisted the extremely strong pressures to modify their programs and policies to optimize apparent "success rates". Predictably, but unfortunately, these pressures have influenced the actions of some other IVF centers very heavily. We once again refer readers to our earlier article with its recommendations for a sound approach to selection of an IVF center. The strategy described there is also effective for identifying high quality physicians and organizations to meet other health needs. Simple formulas, and the reliance on statistics, cannot achieve the desired goals. A system unsound in principle can not, and should not, be relied upon in practice.