Frozen embryos were used in approximately 15% of all ART cycles performed in 2005 (20,657 cycles). Figure 42 compares the success rates for frozen embryos with the success rates for fresh embryos among women using their own eggs. Because some embryos do not survive the thawing process, the percentage of thawed embryos that resulted in live births is usually lower than the percentage of transfers resulting in live births. In 2005, the success rates for frozen embryos were lower than the success rates for fresh embryos. However, the average number of embryos transferred was similar for cycles using both frozen embryos and fresh embryos (see the national summary table for information on the average number of embryos transferred for these cycles). It is important to note that cycles using frozen embryos are both less expensive and less invasive than those using fresh embryos because the woman does not have to go through the fertility drug stimulation and egg retrieval steps again.

Figure 42: Success Rates for ART Cycles Using Frozen Embryos and Fresh Embryos, 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.

Part A of Figure 43 shows that among the 6,721 pregnancies that resulted from ART cycles using frozen nondonor embryos, 68% were singleton pregnancies, 20% were twins, and 3% were triplets or more. Nine percent of pregnancies ended in miscarriage 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 (23%).

In 2005, 5,275 pregnancies from ART cycles that used frozen nondonor embryos resulted in live births. Part B of Figure 43 shows that approximately 23% of these live births produced more than one infant (21% twins and 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 for 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.