Section 2: ART Cycles Using Fresh, Nondonor Eggs or Embryos (Part C)

Figure 27 shows the relationship between the success of ART cycles performed in 2008 using fresh nondonor eggs or embryos and a history of both previous ART cycles and previous births. We do not have information on whether the previous births were the result of ART or were conceived naturally. However, among women with previous births, percentages of ART cycles that resulted in live births among women who did not undergo a previous ART procedure were comparable to percentages among women who had undergone previous ART cycles.

Although Figure 26 shows that having undergone previous ART cycles may be related to the success of the current ART cycle, it is also important to consider the outcomes of previous cycles and whether the woman has given birth in the past, as demonstrated in this figure.

Figure 28 presents the types of ART procedures performed in 2008 among women using fresh nondonor eggs or embryos. For about 36% of ART procedures that used fresh nondonor eggs or embryos in 2008, standard IVF (in vitro fertilization) techniques were used: eggs and sperm were combined in the laboratory, the resulting embryos were cultured for 2 or more days, and one or more embryos were then transferred into the woman’s uterus through the cervix.

For most of the remaining ART procedures (about 64%), fertilization was accomplished using intracytoplasmic sperm injection (ICSI). This technique involves injecting a single sperm directly into an egg; the embryos are then cultured and transferred as in standard IVF.

For a small proportion of ART procedures, unfertilized eggs and sperm (gametes) or early embryos (zygotes) were transferred into the woman’s fallopian tubes. These procedures are known as gamete and zygote intrafallopian transfer (GIFT and ZIFT). Some women with tubal infertility are not suitable candidates for GIFT and ZIFT. GIFT and ZIFT are more invasive procedures than IVF because they involve inserting a laparoscope into a woman’s abdomen to transfer the embryos or gametes into the fallopian tubes. In contrast, IVF involves transferring embryos or gametes into a woman’s uterus through the cervix without surgery.

Figure 29 shows the percentage of egg retrievals that resulted in live births for each type of ART procedure started in 2008. ART procedures that used a combination of IVF had the highest percentage (40%) of egg retrievals that resulted in live births and the percentage for the two predominant types of ART, IVF without ICSI and IVF with ICSI, was similar (34% and 33% respectively). See Figures 30–32 and Figures 52–54 for further details on IVF procedures that used ICSI.

ICSI was developed to overcome problems with fertilization that sometimes occur in couples diagnosed with male factor infertility. Figure 30 shows the percentage of fresh nondonor cycles using ICSI in 2008 among couples with and without diagnoses of male factor infertility. In 2008, 67,258 ICSI cycles were performed. Slightly less than half of the ICSI cycles were performed for couples with a diagnosis of male factor infertility. However, diagnostic procedures may vary from one clinic to another, so the categorization of causes of infertility may also vary.

ICSI was developed to overcome problems with fertilization that sometimes occur among couples diagnosed with male factor infertility. In 2008, 83% of couples diagnosed with male factor infertility used IVF with ICSI. Because ICSI can only be performed when at least one egg has been retrieved, Figure 31 presents percentages of retrievals that resulted in live births for these ICSI procedures among couples diagnosed with male factor infertility. For comparison, these percentages are presented alongside percentages for ART cycles that used standard IVF without ICSI among couples with all diagnoses except male factor infertility.

For every age group, when ICSI was used for couples diagnosed with male factor infertility, percentages of retrievals that resulted in live births were similar to those achieved by couples who used standard IVF without ICSI and were not diagnosed with male factor infertility. Please note, however, the definitions of infertility diagnoses may vary from clinic to clinic and that a review of select clinical records revealed that reporting of infertility causes may be incomplete. (See Findings from Validation Visits for 2008 ART Data in Appendix A for additional information.) Therefore, differences in success rates by causes of infertility should be interpreted with caution.

As shown in Figure 30, a large number of ICSI procedures are now performed even when couples are not diagnosed with male factor infertility. Figure 32 presents percentages of egg retrievals that resulted in live births for those cycles compared with ART cycles among couples who used IVF without ICSI. For every age group, the ICSI procedures were less successful. Please note, however, the definitions of infertility diagnoses may vary from clinic to clinic and that a review of select clinical records revealed that reporting of infertility causes may be incomplete. (See Findings from Validation Visits for 2008 ART Data in Appendix A for additional information.) Additionally, information was not available to determine whether this finding was a direct effect of the ICSI procedure or whether the patients who used ICSI were somehow different from those who use IVF alone. Therefore, differences in success rates by causes of infertility should be interpreted with caution.

Figure 33 shows that approximately 38% of ART cycles that used fresh nondonor eggs or embryos and progressed to the embryo transfer stage in 2008 involved the transfer of three or more embryos, about 13% of cycles involved the transfer of four or more, and approximately 4% of cycles involved the transfer of five or more embryos.

Figure 34 presents the relationship between the implantation percentage (see Implantation rate in Glossary of Terms) for fresh nondonor embryos transferred and a woman’s age. The percentage of embryos transferred that resulted in implantation was highest (34%) among women younger than 35. However, the implantation percentage decreased steadily as the age of the woman increased. Specifically, the implantation percentage was lowest (2%) among women older than 44 compared with the implantation percentage among women in each of the other age groups.

Figure 35 shows the relationship between the number of embryos transferred during an ART procedure in 2008 and the number of live births as a result of that procedure. The percentage of transfers that resulted in live births increased when two or more embryos were transferred; however, transferring multiple embryos also poses a risk of having a multiple-infant birth. Multiple-infant births cause concern because of the additional health risks they create for both mothers and infants. Also, pregnancies with multiple fetuses are potentially subject to multifetal reduction. This can happen naturally (e.g., fetal death), or a woman and her doctor may decide to reduce the number of fetuses using a procedure called multifetal pregnancy reduction. CDC does not collect information on multifetal pregnancy reductions.

The relationships between number of embryos transferred, percentages of transfers resulting in live births, and multiple-infant births are complicated by several factors, such as the woman’s age and embryo quality. See Figure 36 for more details on women most at risk for multiple births.

Although, in general, transferring more than one embryo tends to improve the chance for a successful ART procedure (see Figure 35), other factors are also important. Previous research suggests that the number of embryos fertilized and thus available for ART is just as, if not more, important in predicting success as the number of embryos transferred. Additionally, younger women tend to have both higher percentages of live births and higher likelihood of multiple-infant births. Figure 36 shows the relationship between the number of embryos transferred, percentages of transfers resulting in live births, and multiple-infant births for a subset of ART procedures in which the woman was younger than 35 and the couple chose to set aside some embryos for future cycles rather than transfer all available embryos at one time.

For this group, the chance for a live birth using ART was about 49% when only one embryo was transferred. If one measures success as the percentage of transfers resulting in singleton live births, the highest likelihood of live birth was observed with only one embryo transferred.

The proportion of live births that were multiple-infant births was about 42% with two embryos and 48% with five or more embryos transferred. In summary, as the number of embryos transferred increased, the proportion of live births that were multiple-infant births also increased.

Once an ART cycle has progressed from egg retrieval to fertilization, the embryo(s) can be transferred into the woman’s uterus in the subsequent 1 to 6 days. Figure 37 shows that in 2008 approximately 56% of embryo transfers occurred on day 3. Day 5 embryo transfers were the next most common, accounting for about 35% of ART procedures that progressed to the embryo transfer stage.

As shown in Figure 37, in the vast majority of ART procedures, embryos were transferred on day 3 (56%) or day 5 (35%). Figure 38 compares percentages of day 3 embryo transfers that resulted in live births with those for day 5 embryo transfers. In all age groups, percentages were higher for day 5 embryo transfers than for day 3 transfers. However, some cycles do not progress to the embryo transfer stage because of embryo arrest (interruption in embryo development) between day 3 and day 5. These cycles are not accounted for in percentages of day 5 transfers that resulted in live births. Therefore, differences in percentages of day 3 and day 5 transfers that result in live births should be interpreted with caution.

Figure 39 shows the number of embryos transferred on day 3 and day 5. Overall, fewer embryos were transferred on day 5 than on day 3. Approximately 50% of day 3 embryo transfers and 20% of day 5 embryo transfers involved the transfer of three or more embryos. The decrease in the number of embryos transferred on day 5; however, did not translate into a lower risk for multiple-infant births. See Figure 40 for more details on the relationship between multiple-infant birth risk and day of embryo transfer.

Multiple-infant births are associated with greater problems for both mothers and infants, including higher rates of caesarean section, prematurity, low birth weight, and infant disability or death.

Part A of Figure 40 shows that among the 15,124 live births that occurred following day 3 embryo transfer, about 72% were singletons, 26% were twins, and 2% were triplets or more. Thus, approximately 28% of these live births produced more than one infant.

In 2008, 13,892 live births occurred following day 5 embryo transfer. Part B of Figure 40 shows that approximately 36% of these live births produced more than one infant (34% twins and 2% triplets or more).

As shown in Figure 39, fewer embryos were transferred on day 5 than on day 3. However, the proportion of live births resulting in twins is higher among transfer procedures performed on day 5 than on day 3. Thus, the risk of having a multiple-infant birth was higher for day 5 embryo transfers. The likelihood of multiple-infant births for both day 3 and day 5 embryo transfers is much higher overall than for multiple-infant births in the general U.S. population (about 3%).

As shown in Figures 39 and 40, embryos transferred on day 5 result in more multiple-infant births compared with embryos transferred on day 3, despite the smaller number of embryos transferred on day 5. Figure 41 shows the relationship between the number of embryos transferred, the percentage of transfers resulting in live births, and the percentage of multiple-infant births for day 5 embryo transfer procedures in which the woman was younger than 35 and the couple decided to set aside some embryos for future cycles rather than transfer all available embryos at one time.

The percentage of transfers resulting in live births was the highest (about 60%) when two embryos were transferred; however, the proportion of live births that were multiples (twins or more)—which present a higher risk for poor health outcomes—was 46%. The percentage of live births that were higher-order multiples (triplets or more) was much higher when three or more embryos were transferred on day 5 (approximately 9%) than for those involving the transfer of just two embryos on day 5 (approximately 1%).

If one measures success as the percentage of transfers resulting in singleton live births, the highest percentage (53%) was observed with the transfer of a single embryo on day 5.

In some cases a woman has trouble carrying a pregnancy. In such cases the couple may use ART with a gestational carrier, sometimes called a surrogate. A gestational carrier is a woman who agrees to carry the developing embryo for a couple with infertility problems. Gestational carriers were used in about 1% of ART cycles using fresh nondonor embryos in 2008 (915 cycles). Figure 42 compares percentages of transfers that resulted in live births for ART cycles that used a gestational carrier in 2008 with cycles that did not. In all age groups, percentages of transfers that resulted in live births for ART cycles that used gestational carriers were higher than for those cycles that did not.