Section 2: ART Cycles Using Fresh, Nondonor Eggs or Embryos (Part A)
Section 2 it is broken up into three parts. Part A contains Figures 6–15.
Figure 6 presents the steps for an ART cycle using fresh nondonor eggs or embryos and shows how ART users in 2010 progressed through these stages toward pregnancy and live birth.
An ART cycle is started when a woman begins taking medication to stimulate the ovaries to develop eggs or, if no drugs are given, when the woman begins having her ovaries monitored (using ultrasound or blood tests) for natural egg production.
If eggs are produced, the cycle then progresses to egg retrieval, a surgical procedure in which eggs are collected from a woman’s ovaries.
Once retrieved, eggs are combined with sperm in the laboratory. If fertilization is successful, one or more of the resulting embryos are selected for transfer, most often into a woman’s uterus through the cervix (IVF), but sometimes into the fallopian tubes (GIFT, or ZIFT).
If one or more of the transferred embryos implant within the woman’s uterus, the cycle then may progress to clinical pregnancy.
Finally, the pregnancy may progress to a live birth, the delivery of one or more live-born infants. (The birth of twins, triplets, or more is counted as one live birth.)
A cycle may be discontinued at any step for specific medical reasons (e.g., no eggs are produced, the embryo transfer was not successful) or by patient choice.
In 2010, 10,583 ART cycles (about 10% out of all 100,824 cycles using fresh nondonor eggs or embryos) were discontinued before the egg retrieval step (see Figure 6). Figure 7 shows reasons that the cycles were discontinued. For approximately 84% of these cycles, there was no or inadequate egg production. Other reasons included a too-high response to ovarian stimulation medications (i.e., potential for ovarian hyperstimulation syndrome), concurrent medical illness, or a patient withdrawal for other reasons.
Figure 8 shows success rates using six different measures for ART cycles using fresh nondonor eggs or embryos in 2010, each providing slightly different information about this complex process. The vast majority of success rates have increased slightly each year since CDC began monitoring them in 1995 (see Section 5).
- Percentage of ART cycles started that produced a pregnancy: This is higher than the percentage of cycles that resulted in a live birth because some pregnancies end in miscarriage, induced abortion, or stillbirth (see Figure 10).
- Percentage of ART cycles started that resulted in a live birth (a delivery of one or more live-born infants): This is the one many people are most interested in because it represents the average chance of having one or more live-born infants by using ART. This is referred to as the basic live birth rate in the Fertility Clinic Success Rate and Certification Act of 1992.
- Percentage of ART cycles in which eggs were retrieved that resulted in a live birth: This is generally higher than the percentage of cycles that resulted in a live birth because it excludes cycles that were canceled before eggs were retrieved. This is referred to as the live birth rate per successful oocyte (egg) retrieval in the Fertility Clinic Success Rate and Certification Act of 1992.
- Percentage of ART cycles in which an embryo or egg and sperm transfer occurred that resulted in a live birth: This is one of the highest of these six measures of ART success because it excludes cycles that did not proceed to embryo transfer.
- Percentage of ART cycles started that resulted in a singleton live birth: This is important because singleton live births have a much lower risk than multiple-infant births for adverse infant health outcomes, including prematurity, low birth weight, disability, and death.
- Percentage of ART cycles in which an embryo or egg and sperm transfer occurred that resulted in a singleton live birth: This is higher than the percentage of ART cycles started that resulted in a singleton live birth because not all ART cycles proceed to embryo transfer.
Figure 9 shows the outcomes of ART cycles in 2010 that used fresh nondonor eggs or embryos. Most of these cycles (approximately 62%) did not produce a pregnancy; a very small proportion (less than 1%) resulted in an ectopic pregnancy (the embryo implanted outside the uterus), and about 37% resulted in clinical pregnancy. Clinical pregnancies can be further subdivided as follows:
- 63% of clinical pregnancies resulted in a single-fetus pregnancy.
- 31% resulted in a multiple-fetus pregnancy.
- 6% ended before the number of fetuses could be accurately determined.
Figure 10 shows the outcomes of pregnancies resulting from ART cycles using fresh nondonor eggs or embryos in 2010. Approximately 82% of the pregnancies resulted in a live birth (57% in a singleton birth and about 25% in a multiple-infant birth). About 18% of pregnancies resulted in miscarriage, stillbirth, induced abortion, or maternal death prior to birth. For less than 1% of pregnancies, the outcome was unknown.
Although the birth of more than one infant is counted as one live birth, multiple-infant births are presented here as a separate category because they often are associated with problems for both mothers and infants. Infant deaths and birth defects are not included as adverse outcomes because the available information for these outcomes is incomplete.
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 11 shows that among the 37,191 pregnancies that resulted from ART cycles using fresh nondonor eggs or embryos, approximately 63% were singleton pregnancies and 31% were multiple-fetus pregnancies (28% were twins and 3% were triplets or more). Approximately 6% of pregnancies ended before the number of fetuses could be accurately determined. Therefore, the percentage of pregnancies with more than one fetus might have been higher than what was reported (about 31%).
In 2010, 6,613 pregnancies resulting from ART cycles ended in either miscarriage, stillbirth, induced abortion, or maternal death, and 153 pregnancy outcomes were not reported. The remaining 30,425 pregnancies resulted in live births. Part B of Figure 11 shows that approximately 30% of these live births produced more than one infant (29% twins and approximately 2% triplets or more). This compares with a multiple-infant birth rate of slightly more than 3% in the general U.S. population.
Although total percentages for multiples were similar for pregnancies and live births, there were more triplet or higher order pregnancies than births. Triplet or higher order pregnancies may be reduced to twins or singletons by the time of birth. 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.
Preterm birth occurs when a woman gives birth before 37 full weeks of pregnancy. Low-birth-weight infants are born weighing less than 2,500 grams or 5 pounds, 9 ounces. Infants born preterm or with low birth weight are at greater risk of death in the first few days of life, as well as other adverse health outcomes, including visual and hearing impairments, intellectual and learning disabilities, and behavioral and emotional problems throughout life. Preterm births and low-birth-weight infants also cause substantial emotional and economic burdens for families.
Figure 12 shows percentages of preterm births and low-birth-weight infants resulting from ART cycles that used fresh nondonor eggs or embryos in 2010, by number of infants born. For singletons, it shows separately the percentage of preterm birth and low birth weight among infants born from pregnancies that started with one fetus (single-fetus pregnancies) and with more than one fetus (multiple-fetus pregnancies). Among singletons, the percentage of preterm births and low-birth-weight infants was higher for those from multiple-fetus pregnancies. In the general U.S. population, where singletons are almost always the result of a single-fetus pregnancy, 12% were born preterm and 8% had low birth weights in 2008 (most recent available data).
Taking the number of preterm births or low-birth-weight infants in the general population and comparing it with multiple-fetus pregnancies resulting from ART is not meaningful because a substantial proportion of multiple-infant births are due to infertility treatments (both ART and non-ART). These data indicate that the risks of preterm birth and low birth weight are higher among infants conceived through ART than for infants in the general population. The increased risks are due, in large part, to the higher percentage of multiple-fetus pregnancies resulting from ART cycles.
Figure 13 presents ART cycles using fresh nondonor eggs or embryos in 2010 according to the age of the woman who had the procedure. About 12% of these cycles were among women younger than age 30, almost 66% were among women aged 30–39, and approximately 23% were among women aged 40 or older.
Do percentages of ART cycles that result in pregnancies, live births, and singleton live births differ among women of different ages?
A woman’s age is the most important factor affecting the chances of a live birth when her own eggs are used. Figure 14 shows percentages of pregnancies, live births, and singleton live births among women of different ages who had ART procedures using fresh nondonor eggs or embryos in 2010. Percentages of ART cycles resulting in live births and singleton live births are different because of the high percentage of multiple-infant deliveries counted among the total live births. The percentage of multiple-infant births is particularly high among women younger than 35 (see Figure 33). Among women in their 20s, percentages of ART cycles resulting in pregnancies, live births, and singleton live births were relatively stable; however, percentages declined steadily among women in their mid-30s onward. For additional detail on percentages of ART cycles that resulted in pregnancies, live births, and singleton live births among women aged 40 or older, see Figure 15.
How do percentages of ART cycles that result in pregnancies, live births, and singleton live births differ among women aged 40 or older?
Figure 15 shows percentages of pregnancies, live births, and singleton live births among women aged 40 or older who used fresh nondonor eggs or embryos in 2010. The percentage of ART cycles resulting in pregnancy was nearly 27% among women aged 40; the percentage of ART cycles resulting in live births for this age was about 18%, and the percentage of ART cycles resulting in singleton live births was about 15%. All percentages dropped steadily with each 1-year increase in age. Among women older than 44, percentages of live births and singleton live births were both 1% or less. Women aged 40 or older generally have much higher percentages of live births using donor eggs (see Figure 44).