Figure 49 shows the numbers of ART cycles performed, live-birth deliveries, and infants born using ART from 1996 through 2005. The number of ART cycles performed in the United States has more than doubled, from 64,681 cycles in 1996 to 134,260 in 2005. The number of live-birth deliveries in 2005 (38,910) was more than two and a half times higher than in 1996 (14,507). The number of infants born who were conceived using ART also increased steadily between 1996 and 2005. In 2005, 52,041 infants were  born, which was more than double the 20,840 born in 1996. Because in some cases more than one infant is born during a live-birth delivery (e.g., twins), the total number of infants born is greater than the number of live-birth deliveries.

Figure 50 presents the percentages of transfers that resulted in live births for the four primary types of ART cycles. Percentages of transfers that resulted in live births are presented rather than percentages of cycles that resulted in live births because that is the only way to directly compare cycles using fresh embryos with those using frozen embryos.

From 1996 through 2005, the percentage of transfers resulting in live births for fresh–nondonor cycles increased 22%, from 28% in 1996 to 34% in 2005. Over the same time period, the percentage of transfers resulting in live births increased 68% for frozen–nondonor cycles, 34% for fresh–donor cycles, and 49% for frozen–donor cycles.

Singleton live births are an important measure of success because they have a much lower risk than multiple-infant births for adverse infant health outcomes, including prematurity, low birth weight, disability, and death. Figure 51 presents percentages of transfers that resulted in singleton live births for the four primary types of ART cycles. Percentages of transfers that resulted in singleton live births are presented rather than percentages of cycles that resulted in singleton live births because that is the only way to directly compare cycles using fresh embryos with those using frozen embryos.

From 1996 through 2005, the percentage of transfers that resulted in singleton live births for fresh–nondonor cycles increased 35%, from 17% in 1996 to 23% in 2005. Over the same time period, the percentage of transfers resulting in singleton live births increased 79% for frozen–nondonor cycles, 36% for fresh–donor cycles, and 48% for frozen–donor cycles.

Figure 52 presents percentages of transfers that resulted in live births, by woman’s age, for ART cycles using fresh nondonor eggs or embryos.

From 1996 through 2005, the percentage of transfers that resulted in live births for women younger than 35 increased 29%, from 34% in 1996 to 43% in 2005. Over the same time period, the percentage of transfers that resulted in live births increased 24% for women 35–37, 18% for women 38–40, 30% for women 41–42, and 7% for women older than 42.

Figure 52: Percentages of Transfers That Resulted in Live Births for ART Cycles Using Fresh Nondonor Eggs or Embryos, by Womans Age, 1996–2005.

Singleton live births are an important measure of success because they have a much lower risk than multiple-infant births for adverse infant health outcomes, including prematurity, low birth weight, disability, and death. Figure 53 presents percentages of transfers that resulted in singleton live births, by woman’s age, for ART cycles using fresh nondonor eggs or embryos.

From 1996 through 2005, the percentage of transfers that resulted in singleton live births for women younger than 35 increased about 45%, from 19% in 1996 to 28% in 2005. Over the same time period, the percentage of transfers that resulted in singleton live births increased 36% for women 35–37, 23% for women 38–40, 34% for women 41–42, and 11% for women older than 42.

Figure 54 presents the trends for number of embryos transferred in fresh–nondonor cycles that progressed to the embryo transfer stage. From 1996 to 2005, cycles that involved the transfer of one embryo increased slightly, from 6% to 9%; cycles that involved the transfer of two embryos increased dramatically, from 10% in 1996 to 43% in 2005. Cycles that involved the transfer of three embryos increased from 23% in 1996 to 29% in 2005, and cycles that involved the transfer of four or more embryos decreased from 62% in 1996 to 18% in 2005.

As shown in Figure 54, the number of embryos transferred in fresh–nondonor cycles has decreased during the past 10 years. Figure 55 shows the change over time in the number of embryos transferred for 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. Previous research suggests that the number of embryos available for an ART cycle is important in predicting success. Younger women also tend to have higher success rates (see Figure 14).

Overall, the number of embryos transferred decreased among couples who chose to transfer fewer embryos than were available. In 1996, almost two-thirds (64%) of ART cycles involved the transfer of  four or more embryos; 33%, three embryos; 3%, two embryos; and less than 1%, one embryo. By 1998, the percentage of cycles in which four or more embryos were transferred had decreased to 33%; half of all ART cycles involved the transfer of three embryos; 16% of cycles, two embryos; and less than 1%, one embryo. By 2005, four or more embryos were transferred in only 4% of cycles, three in 20% of cycles, two in more than two-thirds (72%) of cycles, and one in 4% of cycles.

Figure 56 presents success rates by the number of embryos transferred for ART cycles using  fresh nondonor eggs or embryos from 1996 through 2005. In general, success rates were higher when two or more embryos were transferred. From 1996 through 2005, the success rates almost tripled, from 14% to 41%, for ART cycles that involved the transfer of two embryos. The success rates also increased for ART cycles that involved the transfer of either one or three embryos; however, the success rates decreased 13%, from 32% to 28%, for ART cycles that involved the transfer of four or more embryos.

The relationship between number of embryos transferred and success rates is complicated by several  factors, such as the woman’s age and embryo quality. Trends over time may reflect changes in these factors.

Figure 57 shows changes over time in the number of embryos transferred and the percentage of transfers that resulted in live births for ART cycles in which the woman was younger than 35 and chose to set aside some embryos for future cycles rather than transfer all available embryos at one time. Previous research suggests that the number of embryos available for an ART cycle is an important predictor of success. Younger women also tend to have higher success rates (see Figure 14).

For this group of women, the percentage of transfers that resulted in live births generally increased over time, regardless of the number of embryos transferred. The biggest increase was for cycles in which two embryos were transferred. In 1996, the chance for a live birth was highest (41%) when three embryos were transferred; however, in 2005, the chance for a live birth was highest (53%) when two embryos were transferred.

Success rates for cycles involving the transfer of one embryo were comparable to those that involved multiple embryos. Elective single-embryo transfer minimizes the risk for multiple-infant pregnancy and related adverse outcomes. Recently, the Society for Assisted Reproductive Technology (SART) revised its embryo transfer guidelines to encourage single-embryo transfer among patients with good prognoses.

Figure 57: Percentages of Transfers That Resulted in Live Births Among Women Who Were Younger Than 35 and Set Aside Extra Embryos for Future Use, by Number of Embryos Transferred, 1996–2005.

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. Figure  58 shows the percentages of multiple-infant live births for the four primary types of ART procedures.

For fresh-nondonor ART cycles, the percentage of multiple-infant live births decreased 17% since 1996, from 38% of all live births in 1996 to 32% in 2005. Over the same time period, the percentage of multiple-infant live births decreased 16% for frozen–nondonor cycles and 2% for fresh-donor cycles. In all years except 1997, the percentage of multiple-infant live births remained stable for frozen-donor cycles.

Have multiple-infant live births for cycles using fresh nondonor eggs or embryos changed for all ART patients or only for those in particular age groups?

Figure 59 shows that the percentages of multiple-infant live births decreased between 1996 and 2005 for women in all age groups. In 1996, 43% of live-birth deliveries to women younger than 35 were multiple-infant births, compared with 36% in 2005. Among women older than 42, the percentages of multiple-infant live births decreased slightly, from 14% in 1996 to 13% in 2005.