What are the steps for an ART cycle using fresh nondonor eggs or embryos?

Figure 5 presents the steps for an ART cycle using fresh nondonor eggs or embryos and shows how ART users in 2005 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 (e.g., GIFT, 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.

Figure 5: Outcome of ART Cycles Using Fresh Nondonor Eggs or Embryos, by Stage, 2005.

Why are some ART cycles discontinued?

In 2005, 11,729 ART cycles (about 12%) were discontinued before the egg retrieval step (see Figure 5). Figure 6 shows reasons that the cycles were stopped. For approximately 83% of these cycles, there was no or inadequate egg production. Other reasons included too high a response to ovarian stimulation medications (i.e., potential for ovarian hyperstimulation syndrome), concurrent medical illness, or a patient’s personal reasons.

Figure 6: Reasons ART Cycles Using Fresh Nondonor Eggs or Embryos Were Discontinued in 2005.

How is the success of ART measured?

Figure 7 shows ART success rates using six different measures, 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 9).
   
• 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 a live-born infant 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. In 2005, about 12% of all cycles using fresh nondonor eggs or embryos were canceled for a variety of reasons (see Figure 6). 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 the highest of these six measures of ART success.
   
• Percentage of ART cycles started that resulted in a singleton live birth: Overall, 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.

What percentage of ART cycles results in a pregnancy?

Figure 8 shows the results of ART cycles in 2005 that used fresh nondonor eggs or embryos. Most of these cycles (65%) did not produce a pregnancy; a very small proportion (0.6%) resulted in an ectopic pregnancy (the embryo implanted outside the uterus), and 34% resulted in clinical pregnancy. Clinical pregnancies can be further subdivided as follows:

• 20.5% resulted in a single-fetus pregnancy.
• 11.2% resulted in a multiple-fetus pregnancy.
• 2.3% ended in miscarriage before the number of fetuses could be accurately determined.

Figure 8: Results of ART Cycles Using Fresh Nondonor Eggs or Embryos, 2005.

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.

Figure 9: Outcomes of Pregnancies Resulting from ART Cycles Using Fresh Nondonor Eggs or Embryos, 2005.

Using ART, what is the risk of having a multiple-fetus pregnancy or multiple-infant live birth?

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 10 shows that among the 33,101 pregnancies that resulted from ART cycles using fresh nondonor eggs or embryos, 60% were singleton pregnancies, 28% were twins, and about 4% were triplets or more. Seven percent of pregnancies ended in miscarriage in which the number of fetuses could not be accurately determined. Therefore, the percentage of pregnancies with more than one fetus might have been higher than what was reported (about 33%).

In 2005, 5,812 pregnancies resulting from ART cycles ended in either miscarriage, stillbirth, or induced abortion, and 239 pregnancy outcomes were not reported. The remaining 27,047 pregnancies resulted in live births. Part B of Figure 10 shows that approximately 32% of these live births produced more than one infant (30% 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 the total rates for multiples were similar between pregnancies and live births, there were more triplet-or-more pregnancies than births. Triplet-or-more 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.

Figure 10: Risks of Having Multiple-Fetus Pregnancy and Multiple-Infant Live Birth from ART Cycles Using Fresh Nondonor Eggs or Embryos, 2005.

Low-birth–weight infants (less than 2,500 grams, or 5 pounds, 9 ounces) are at increased risk for death and short- and long-term disabilities such as cerebral palsy, mental retardation, and limitations in motor and cognitive skills.

Figure 12 presents percentages of low-birth–weight infants resulting from ART cycles that used fresh nondonor eggs or embryos, by number of infants born. For singletons, it shows separately the rates of 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 born through ART, the percentage of low-birth–weight infants was higher for those from multiple-fetus pregnancies (17%) than those from single-fetus pregnancies (9%). In the general U.S. population, where singletons are almost always the result of a single-fetus pregnancy, 6% of infants born in 2004 (most recent available data) had low birth weights.

Approximately 56% of twins and 92% of triplets or more had low birth weights. Comparing rates of low birth weight between ART twins and triplets or more and the general population is not meaningful because the vast majority of multiple births in the United States are due to infertility treatments (both ART and non-ART).

These data indicate that the risk for low birth weight is higher for infants conceived through ART than for infants in the general population. The increase in risk is due, in large part, to the higher rate of multiple-infant pregnancies resulting from ART cycles.

Figure 12: Percentages of Low Birth Weight Infants from ART Cycles Using Fresh Nondonor Eggs or Embryos, by Number of Infants Born, 2005.

Figure 13 presents ART cycles using fresh nondonor eggs or embryos according to the age of the woman who had the procedure. About 12% of these cycles were among women younger than age 30, 68% were among women aged 30–39, and approximately 21% were among women aged 40 and older.

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 the percentages of pregnancies, live births, and singleton live births for women of different ages who had ART procedures using fresh nondonor eggs or embryos in 2005. The 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 34). Among women in their 20s, the percentages of ART cycles resulting in pregnancies, live births, and singleton live births were relatively stable; however, success rates declined steadily from the mid-30s onward. For additional detail on success rates among women aged 40 or older, see Figure 15.

Figure 14: Percentages of ART Cycles Using Fresh Nondonor Eggs or Embryos That Resulted in Pregnancies, Live Births, and Singleton Live Births, by Age of Woman, 2005.

Success rates decline with each year of age and are particularly low for women 40 or older. Figure 15 shows the percentages of pregnancies, live births, and singleton live births in 2005 for women 40 or older who used fresh nondonor eggs or embryos. The average chance for pregnancy was 23% for women age 40; the percentage of ART cycles resulting in live births for this age was about 16%, and the percentage of ART cycles resulting in singleton live births was about 13%. All percentages dropped steadily with each 1-year increase in age. For women older than 44, the percentages of live births and singleton live births were both a little less than 1%. Women 40 or older generally have much higher success rates using donor eggs (see Figure 45).

Figure 15: Percentages of ART Cycles Using Fresh Nondonor Eggs or Embryos That Resulted in Pregnancies, Live Births, and Singleton Live Births Among Women Aged 40 or Older, 2005.

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