2007 ART Report Section 3-ART Cycles Using Frozen Nondonor Embryos

Frozen embryos were used in approximately 16% of all ART cycles performed in 2007 (23,133 cycles). Figure 42 compares percentages of transfers that resulted in live births and singleton live births for frozen embryos with those for fresh embryos among women using their own eggs. Because some embryos do not survive the thawing process, the percentage of thawed embryos that result in live births is usually lower than the percentage of transfers resulting in live births. In 2007, percentages for frozen embryos were lower than for fresh embryos. However, the average number of embryos transferred was similar for cycles using frozen embryos and those using fresh embryos (see the national summary 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.

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 8,111 pregnancies that resulted from ART cycles using frozen nondonor embryos, approximately 66% were singleton pregnancies, 21% were twins, and 3% were triplets or more. Almost 10% 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 (24%).

In 2007, 6,365 pregnancies from ART cycles that used frozen nondonor embryos resulted in live births. Part B of Figure 43 shows that approximately 24% of these live births produced more than one infant. 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.