Frozen embryos may yield better pregnancy outcomes
Low birth weight (LBW) and preterm birth are more frequent in babies born through assisted reproductive techniques (ART), a study from Australia shows. The study also shows that use of fresh rather than frozen embryos appears to be one risk factor for these outcomes.
The number of births after the use of ART has increased steadily around the world, especially in developed countries, Dr. Michael Chapman of the University of New South Wales and colleagues note in the journal Fertility and Sterility. “The benefits of ART are evident in that almost 1 in 50 births were associated with ART procedures in Australia in 2001,” they write.
However, ART has been tied to an increased number of adverse birth outcomes, most notably multiple births and preterm and LBW deliveries.
Chapman’s team set out to investigate the frequency of premature births following ART pregnancies in Australia, and to identify any maternal characteristics or fertility procedures that might increase the risk.
Their analysis included 17,726 infants born after 15,035 cycles of ART. They compared outcomes to all Australian births for 1999.
Nearly one third of the ART infants were born preterm, and one quarter were LBW, the researchers found. Both preterm birth and LBW were more common in singletons and twins born through ART, and were also more common among nulliparous women (those delivering their first child).
They also observed that preterm birth was 30 percent more likely among infants conceived with fresh compared to frozen embryos, while LBW was 50 percent more common with fresh rather than frozen embryos.
Both LBW and preterm birth were also more common among couples with female-factor infertility compared to male-factor infertility.
The better results seen with frozen embryos may have been due to higher quality embryos being chosen for freezing, the researchers note, as well as the fact that couples having excess embryos available for freezing may have had better-quality eggs to start with.
SOURCE: Fertility and Sterility June 2005.
Revision date: June 14, 2011
Last revised: by David A. Scott, M.D.