This report marks the tenth consecutive year that CDC has published
an annual report detailing the success rates for ART clinics in the
United States. Having several years of data provides us with the
opportunity to examine trends in ART use and success rates over
time. Because the first year of data collection, 1995, did not
include non-SART member clinics, we limit our examination of trends
to the years 1996–2004.Is the use of ART increasing?
Figure 45 shows the numbers of ART
cycles performed, live-birth deliveries, and infants born using ART from
1996 through 2004. The number of ART cycles performed in the United
States has almost doubled, from 64,681 cycles in 1996 to 127,977 in
2004. The number of live-birth deliveries in 2004 (36,760) was about 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 2004. In 2004, 49,458 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 45: Numbers of ART Cycles
Performed, Live-Birth Deliveries, and Infants Born Using ART, 1996–2004.
Are live birth rates improving?
Figure 46
presents live birth rates for the four primary types of ART cycles.
Live birth rates are presented per transfer rather than per cycle
because that is the only way to directly compare cycles using fresh
embryos with those using frozen embryos.
From 1996 through 2004, the live birth rates for
fresh–nondonor cycles increased 21%, from 28% in 1996 to 34% in
2004. Over the same time period, live birth rates increased 47% for
frozen–nondonor cycles, 30% for fresh–donor cycles, and 66% for
frozen–donor cycles.
Figure 46: Live Births per
Transfer, by Type of ART Cycle, 1996–2004.
Are singleton live birth rates improving?
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 47 presents singleton live birth rates for the four
primary types of ART cycles. Singleton live birth rates are presented
per transfer rather than per cycle because that is the only way to
directly compare cycles using fresh embryos with those using frozen
embryos.
From 1996 through 2004, the singleton live birth rates for fresh–nondonor
cycles increased 34%, from 17% in 1996 to 23% in 2004. Over the same
time period, singleton live birth rates increased 72% for frozen–nondonor
cycles, 33% for fresh–donor cycles, and 47% for frozen– donor cycles.
Figure 47: Singleton Live Births per
Transfer, by Type of ART Cycle, 1996–2004.
Are live birth rates improving for all ART patients or
only for those in particular age groups?
Figure 48
presents live birth rates per transfer, by woman’s age, for ART
cycles using fresh nondonor eggs or embryos.
From 1996 through 2004, the live birth rates for
women younger than 35 increased 27%, from 34% in 1996 to 43% in
2004. Over the same time period, live birth rates increased 22% for
women 35–37, 17% for women 38–40, 29% for women 41–42, and 13% for
women older than 42.
Figure 48: Live Births per Transfer
for ART Cycles Using Fresh Nondonor Eggs or Embryos, by Woman’s Age,
1996–2004.
Are singleton live birth rates improving for all ART
patients or only for those in particular age groups?
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 49 presents singleton
live birth rates per transfer, by woman’s age, for ART cycles using
fresh nondonor eggs or embryos.
From 1996 through 2004, the singleton live birth
rate for women younger than 35 increased about 41%, from 19% in 1996
to 27% in 2004. Over the same time period, live birth rates
increased 33% for women 35–37, 23% for women 38–40, 29% for women
41–42, and 22% for women older than 42.
Figure 49: Singleton Live Births per
Transfer for ART Cycles Using Fresh Nondonor Eggs or Embryos, by Woman’s
Age, 1996–2004.
Has the number of embryos transferred
in fresh–nondonor cycles changed?
Figure 50
presents the trends for number of embryos transferred in fresh–nondonor
cycles that progressed to the embryo transfer stage. From 1996 to
2004, cycles that involved the transfer of one embryo increased
slightly, from 6% to 8%; cycles that involved the transfer of two
embryos increased dramatically, from 10% in 1996 to 39% in 2004.
Cycles that involved the transfer of three embryos increased from
23% in 1996 to 32% in 2004, and cycles that involved the transfer of
four or more embryos decreased from 62% in 1996 to 21% in 2004.
Figure 50:
Percentage of Fresh–Nondonor Cycles That Involved the Transfer of
One, Two, Three, or Four or More Embryos, 1996–2004.
Has the number of embryos transferred in each ART
cycle changed for women younger than 35 who have more embryos available
than they choose to transfer?
As shown in Figure 50, the number of
embryos transferred in fresh–nondonor cycles has decreased during the
past 9 years. Figure 51 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 31).
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; and only 3%, two embryos. 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, and 17% of cycles, two embryos. By 2004, four or more embryos
were transferred in only 5% of cycles, three in 25% of cycles, and two
in more than two-thirds (70%) of cycles.
Figure 51: Percentage of Fresh–Nondonor
Cycles That Involved the Transfer of Two, Three, or Four or More Embryos
in Women Who Were Younger Than 35 and Set Aside Extra Embryos for Future
Use, 1996–2004.
Have there been improvements in
live birth rates, by number of embryos transferred?
Figure 52
presents live birth rates per transfer, by number of embryos
transferred, for ART cycles using fresh nondonor eggs or embryos
from 1996 through 2004. In general, the live birth rate was higher
when two or more embryos were transferred. From 1996 through 2004,
the live birth rate almost tripled, from 14% to 40%, for ART cycles
that involved the transfer of two embryos. The live birth rates also
increased for ART cycles that involved the transfer of either one or
three embryos; however, live birth rates decreased 9%, from 32% to
29%, 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 52: Live
Births per Transfer, by Number of Embryos Transferred, 1996–2004.
Have live birth rates improved
for women younger than 35 who have more embryos available than they
choose to transfer?
Figure 53 shows
changes over time in the relationship between live birth rates and
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 an important predictor of success.
Younger women also tend to have higher success rates (see
Figure 31).
For this group, live birth rates increased over time
for transfers involving any number of embryos. The increase in
success rates was largest when two embryos were transferred. In
1996, the chance for a live birth using ART was highest (41%) when
three embryos were transferred; however, in 2004, the chance for a
live birth using ART was highest (53%) when two embryos were
transferred.
Figure 53: Live
Births per Transfer in Women Who Were Younger Than 35 and Set Aside
Extra Embryos for Future Use, by Number of Embryos Transferred,
1996–2004.
Have multiple-infant birth rates
changed?
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 54
shows the multiple-infant birth rates for the four primary types of
ART procedures.
From 1996 through 2004, the percentage of live-birth
deliveries that were multiple-infant births decreased 15%, from 38%
in 1996 to 33%, for fresh–nondonor cycles. Over the same time
period, the percentage of live-birth deliveries that were
multiple-infant births decreased 10% for frozen–nondonor cycles and
4% for fresh–donor cycles. In all years except 1997, the
multiple-infant birth rates remained stable for frozen–donor cycles.
Figure 54:
Multiple-Infant Births per Live-Birth Delivery, by Type of ART
Cycle, 1996–2004.
Have multiple-infant birth rates
for cycles using fresh nondonor eggs or embryos changed for all ART
patients or only for those in particular age groups?
Figure 55 shows
that the multiple-infant birth rates decreased slightly between 1996
and 2004 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 2004. Among women older than 42, the
multiple-infant birth rates decreased from 14% in 1996 to 8% in
2004.
Figure 55:
Multiple-Infant Births per Live-Birth Delivery, for Fresh–Nondonor
Cycles, by Woman’s Age, 1996–2004.
Have the percentages of
singletons, twins, and triplets or more changed for ART cycles using
fresh nondonor eggs or embryos?
Figure 56
presents the trends in live birth rates and percentage of
multiple-infant births for ART cycles using fresh nondonor eggs or
embryos. Overall, live birth rates per transfer increased from 28%
in 1996 to 35% in 2003 and decreased slightly, to 34%, in 2004. From
1996 to 2004, the percentage of singleton live births increased from
62% to 67%; the percentage of twin births remained stable, ranging
from 30% to 32%; and the percentage of triplet-or-more births
decreased from 7% in 1996 to 3% in 2004.
It is important to note that twins, albeit to a
lesser extent than triplets or more, are still at substantially
greater risk for illness and death than singletons. These risks
include low birth weight, preterm birth, and neurological
impairments such as cerebral palsy. Both the twin and
triplet-or-more birth rates remain significantly higher for ART
births than for births resulting from natural conception.
Figure 56: Live
Births per Transfer and Percentages of Multiple-Infant Births for
ART Cycles Using Fresh Nondonor Eggs or Embryos, 1996–2004.
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