IVF Success Rates

IVF Success Rates

The Age Factor

The primary indicators for success in IVF are the age of the woman, an appropriate ovarian response to stimulation and a history of previous pregnancy. In general, women aged 35 or younger produce more eggs of higher quality than women in their late thirties and early forties and have a higher success rate for each IVF cycle that they attempt. Two factors appear to contribute to the decreasing pregnancy and live birth rates that are seen in women of more advanced age. First, as women get closer to menopause their ovaries begin to respond less well to the medications used to stimulate egg production, even though they continue to ovulate on their own each month. This decrease in so-called ovarian reserve can be measured by obtaining blood tests for FSH and estrogen on day three of the menstrual cycle.

Women with abnormally increased FSH, especially in association with advanced age, tend to produce fewer eggs with stimulation and have a statistically lower pregnancy rate. Some younger women may also demonstrate decreased ovarian reserve, however, this does not appear to have as severe an impact on the pregnancy rates of younger women as it does for older women. In some cases, a change in the stimulation regimen, using higher doses of medication and/or a flare protocol of Lupron, may overcome the decreased ovarian response. However, it is important to remember that a high quality embryo may still result when only a small number of eggs are obtained.

The second reason for the lower success rates that are seen as women age beyond 35 years is the increasing tendency to produce embryos with abnormal numbers of chromosomes as women get older. These abnormal embryos fail to develop normally, resulting in a decline in pregnancy rates, an increase in miscarriage rates, and an increase in babies born with chromosomal abnormalities such as Down's syndrome. Unfortunately, there is no way to test for potential embryo quality prior to an IVF cycle. However, preimplantation genetic diagnosis (PGD) can provide information about the chromosomal makeup of individual embryos in selected cases.

Pregnancy Rates and Multiple Pregnancy Rates

The number of embryos transferred to the uterus influences both the overall pregnancy rate and the multiple pregnancy rate. We generally recommend transferring more embryos in older women compared with younger women due to the increased potential for genetically abnormal embryos as women age beyond 35 years. However, transferring more than the recommended number of embryos does not necessarily increase pregnancy rates as much as it increases the potential for high-order multiple pregnancies (triplets and quadruplets). While the presence of twins presents an increased risk of premature delivery, this risk is usually manageable. However, with three or more babies, the risk of premature birth increases dramatically, resulting in a significant risk to the health and survival of the infants.

In order to reduce the number of high-order multiple pregnancies, guidelines for the number of embryos to be replaced have been established based on the woman’s age, ranging from two embryos for younger women up to four embryos for women in their forties. Younger women with high quality embryos may also opt for a single embryo transfer with only a slight reduction in pregnancy rates compared with the transfer of two embryos.

Day Three vs. Day Five (Blastocyst) Transfer

On the third day after egg retrieval, when the embryos should have divided to eight cells, it is difficult to predict which embryos have the best potential to achieve a pregnancy. Thus, some IVF programs performing day three transfers will transfer more embryos, even in younger women, to overcome this embryo selection problem and maintain a high pregnancy rate.

However, embryos that progress to the blastocyst stage, which occurs five days after egg retrieval, have demonstrated that they are capable of continued growth both in the laboratory and also presumably in the uterus. Although only 25 to 30 percent of the fertilized eggs from a specific treatment cycle will progress to the blastocyst stage, a day five transfer allows for the selection of fewer high-quality embryos to transfer. This is also the stage of development when embryos normally implant in the uterus in natural cycles. Both factors are thought to contribute to the higher pregnancy rates that follow blastocyst as compared with day three transfers, along with the reduced risk of high-order multiple pregnancies that results from the transfer of fewer embryos.

Interpretation of Published IVF Success Rates

While group success rate statistics are helpful, they do not necessarily reflect the pregnancy potential for an individual. Due to the differences in patient populations seen among various IVF programs, a comparison of clinic success rates may not be meaningful because patient medical characteristics and treatment approaches may vary from clinic to clinic. Unfortunately, some clinics may also actively manipulate their success rates to present their center in a more favorable light.

For example, certain clinics may actively discourage certain types of couples, such as those with a poor reproductive history or multiple IVF failures, from even participating in their program without the use of donor eggs. Other clinics may list certain cycles as "research" and not count them in their overall success rates.

Some IVF clinics use statistical manipulations to inflate their apparent pregnancy rates. The generally accepted IVF pregnancy rate and live birth rate are based on the number of couples who begin drug treatment for a planned IVF cycle (cycles initiated). However, not all women that begin an IVF cycle will respond well to drug stimulation, resulting in cancellation of their egg retrieval. In some cases, there may be no eggs obtained, no eggs fertilized, or no healthy embryos suitable for transfer, again resulting in a canceled cycle. Many clinics, especially with high cancellation rates, advertise their pregnancy rates based on the number of egg retrievals or embryo transfers that they perform, thus eliminating canceled cycles from their calculations.

Since some clinics are more likely than others to cancel cycles that are not progressing well, the clinic "cancellation rate" can be an important determinant of the accuracy of their reported success rates, depending on the calculation performed. While not always the fault of the clinic because of the normal variation in a woman’s fertility potential, a canceled cycle may reflect a poor choice of stimulation drugs or the failure to maintain proper culture conditions for the embryos. Of course, cancellations would not affect pregnancy or live birth rates based on the number of women starting an IVF cycle. But the exclusion of those patients who do not meet the clinic’s expectations for egg or embryo development and do not have an egg retrieval or embryo transfer will increase apparent "per retrieval" or "per transfer" success rate percentages by decreasing the number of patients that are divided into the number of pregnancies and births. Thus, advertised success rates per egg retrieval or per embryo transfer are artificially increased when compared to the true rate based on all women who start an IVF cycle.

The multiple pregnancy rate and especially the "triplet or more" pregnancy rate is also a good indication of a clinic’s proficiency with the IVF process. As mentioned previously, clinics that transfer more than the recommended number of embryos will generally have higher multiple pregnancy rates overall and an increased number of high-order multiple pregnancies with three or more babies. While this may seem desirable, a multiple pregnancy represents a higher risk to the overall health and survival of the babies due to the potential for premature delivery. Thus, the success rate of the clinic should be balanced by the multiple pregnancy rate, especially the "triplet or more" pregnancy rate.

The following table reflects the experience of my own practice over the past 10 years. Overall pregnancy rates and live birth rates are generally consistent with the national average with a slightly lower cancellation rate and multiple pregnancy rate. Note that, to date, there have been no high-order live births of triplets or more due to careful management of the number of embryos transferred.

Per Cycle Success Rates By Age - January 1999 thru December 2016
(Fresh Embryos From Nondonor Eggs) Age of Woman
<35 35-37 38-40 41-42 43-44
Total Cycles Initiated 154 72 91 28 21
Clinical Pregnancy Rate Per Cycle 41% 36% 25% 29% 14%
Live (Ongoing) Birth Rate Per Cycle 34% 32% 16% 14% 5%
Cancellation Rate (Prior to Retrieval) 4% 7% 4% 0% 9%
Average # of Embryos Transferred 2.3 2.2 2.4 2.9 2.4
Live Births with Twins 26% 26% 20% 7% 0%
Live Births with Triplets or More 0% 0% 0% 0% 0%

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