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

Figure 3 presents the steps for an ART cycle using fresh nondonor eggs or embryos and shows how ART users in 2003 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 progresses 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 3: Outcome of ART Cycles Using Fresh Nondonor Eggs or Embryos, by Stage, 2003.

Why are some ART cycles discontinued?

In 2003, 11,430 ART cycles (about 13%) were discontinued before the egg retrieval step (see Figure 3). Figure 4 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 4: Reasons ART Cycles Using Fresh Nondonor Eggs or Embryos Were Discontinued in 2003.

How is the success of an ART procedure measured?

Figure 5 shows ART success rates using six different measures, each providing slightly different information about this complex process. The vast majority of rates have increased slightly each year since CDC began monitoring them in 1995 (see Section 5).

• Pregnancy per cycle rate: the percentage of ART cycles started that produced a pregnancy. This rate is higher than the live birth per cycle rate because some pregnancies end in miscarriage, induced abortion, or stillbirth (see Figure 7).

• Live birth per cycle rate: the percentage of ART cycles started that resulted in a live birth (a delivery of one or more live-born infants). This rate is the one many people are most interested in because it represents the average chances of having a live-born infant by using ART. Throughout this report, live birth rate means live birth per cycle rate unless otherwise specified.

• Live birth per egg retrieval rate: the percentage of ART cycles in which eggs were retrieved that resulted in a live birth. It is generally higher than the live birth per cycle rate because it excludes cycles that were canceled before eggs were retrieved. In 2003, about 13% of all cycles using fresh nondonor eggs or embryos were canceled for a variety of reasons (see Figure 4).

• Live birth per transfer rate: includes only those ART cycles in which an embryo or egg and sperm were transferred back to the woman. This rate is the highest of these six measures of ART success.

• Singleton live birth per cycle rate: the 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.

• Singleton live birth per transfer rate: the percentage of ART cycles that resulted in a singleton live birth among ART cycles in which an embryo or egg and sperm were transferred back to the woman.

Figure 5: Success Rates for ART Cycles Using Fresh Nondonor Eggs or Embryos, by Different Measures, 2003.

What percentage of ART cycles results in a pregnancy?

Figure 6 shows the results of ART cycles in 2003 that used fresh nondonor eggs or embryos. Most of these cycles (65%) did not produce a pregnancy; a very small proportion (0.7%) resulted in an ectopic pregnancy (the embryo implanted outside the uterus), and slightly more than 34% resulted in clinical pregnancy. Clinical pregnancies can be further subdivided as follows:

• 20.3% resulted in a single-fetus pregnancy.
• 12.0% resulted in a multiple-fetus pregnancy.
• 2.1% ended in miscarriage before the number of fetuses could be accurately determined.

Figure 6: Results of ART Cycles Using Fresh Nondonor Eggs or Embryos, 2003.

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 7: Outcomes of Pregnancies Resulting from ART Cycles Using Fresh Nondonor Eggs or Embryos, 2003.

Using ART, what is the risk of having a multiple-fetus pregnancy or multiple-infant 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 8 shows that among the 31,348 pregnancies that resulted from ART cycles using fresh nondonor eggs or embryos, 59% were singleton pregnancies, 29% were twins, and about 6% were triplets or more. Six 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 35%).

In 2003, 5,298 pregnancies resulting from ART cycles ended in either miscarriage, stillbirth, or induced abortion, and 275 pregnancy outcomes were not reported. The remaining 25,775 pregnancies resulted in live births. Part B of Figure 8 shows that approximately 34% of these live births produced more than one infant (31% twins and approximately 3% 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 pregnancies than triplet 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. Information on medical multifetal pregnancy reductions is incomplete and therefore is not provided here.

Figure 8: Risk of Having Multiple-Fetus Pregnancy and Multiple-Infant Live Birth from ART Cycles Using Fresh Nondonor Eggs or Embryos, 2003.

A woman’s age is the most important factor affecting the chances of a live birth when her
own eggs are used. Figure 10 shows the pregnancy rates, live birth rates, and singleton live
birth rates for women of different ages who had ART procedures using fresh nondonor eggs or embryos in 2003. Live birth rates and singleton live birth rates are different because of the high percentage of multiple-birth deliveries counted among the total live births. The percentage of multiple births is particularly high among younger women (see Figure 29). Among women in their 20s, pregnancy rates, live birth rates, and singleton live birth rates were relatively stable; however, success rates declined steadily from the mid-30s onward as fertility declined with age. For additional detail on success rates among women aged 40 years or older, see Figure 11.

Figure 10: Pregnancy Rates, Live Birth Rates, and Singleton Live Birth Rates for ART Cycles Using Fresh Nondonor Eggs or Embryos, by Age of Woman, 2003.

Success rates decline with each year of age and are particularly low for women 40 or older. Figure 11 shows pregnancy rates, live birth rates, and singleton live birth rates for women 40 or older who used fresh nondonor eggs or embryos. The average chance for pregnancy was nearly 23% for women age 40; the live birth rate for this age was about 16%, and the singleton live birth rate was 12%. All rates dropped steadily with each 1-year increase in age. For women age 43, the live birth rates and the singleton live birth rates were both approximately 5%. For women older than 43, the live birth rates and singleton live birth rates were both about 2%. Women 40 or older generally have much higher success rates using donor eggs (see Figure 39).

A woman’s age not only affects the chance for pregnancy when her own eggs are used, but also affects her risk for miscarriage. Figure 12 shows miscarriage rates for women of different ages who became pregnant using ART procedures in 2003. Miscarriage rates were below 13% among women younger than 34. The rates began to increase among  women in their mid-to-late 30s and continued to increase with age, reaching 29% at age 40 and 48% at age 43.

The miscarriage rates observed among women undergoing ART procedures using fresh nondonor eggs or embryos appear to be similar to those reported in various studies of
other pregnant women in the United States.

In 2003, a total of 91,032 cycles using fresh nondonor eggs or embryos were started:

• 39,852 in women younger than 35
• 20,056 in women 35–37
• 18,660 in women 38–40
• 8,185 in women 41–42
• 4,279 in women older than 42

Figure 13 shows that a woman’s chance of progressing from the beginning of ART to pregnancy and live birth (using her own eggs) decreases at every stage of ART as her age increases.

• As women get older, the likelihood of a successful response to ovarian stimulation and progression to egg retrieval decreases.
• As women get older, cycles that have progressed to egg retrieval are slightly less likely to reach transfer.
• The percentage of cycles that progress from transfer to pregnancy also decreases as women get older.
• As women get older, cycles that have progressed to pregnancy are less likely to result in a live birth because the risk for miscarriage is greater (see Figure 12).

Overall, 37% of cycles started in 2003 among women younger than 35 resulted in live births. This percentage decreased to 30% among women 35–37 years of age, 20% among women 38–40, 11% among women 41–42, and 4% among women older than 42. As noted in Figures 10 and 11, the proportion of cycles that resulted in singleton live births is even lower for each age group.

Figure 13: Outcomes of ART Cycles Using Fresh Nondonor Eggs or Embryos, by Stage and Age Group, 2003.

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