July 1, 2005
Frozen embryos may yield better pregnancy outcomes
NEW YORK (Reuters Health) - 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
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
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
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.