June 19, 2006
Japan experts devise new human egg freezing method
By Patricia Reaney
PRAGUE (Reuters) - A new method of freezing human eggs
could enable many more women, particularly young cancer
patients, to have children, Japanese fertility experts said on
Unlike sperm which can be easily frozen, thawed and used in
fertility treatments, women's eggs are very fragile and are
often damaged when they are thawed.
Only about 150 babies worldwide, including three in
Britain, have been born from eggs that have been frozen and
But Japanese researchers told a fertility meeting they have
devised a rapid freezing method that is more effective than the
"By using this method we can obtain a very high thawing
rate," Dr Masashige Kuwayama, of the Kato Ladies clinic in
Tokyo, Japan, told a news conference.
"This technology opens up new horizons for medically
assisted reproduction in women, enabling them to have the
option of having children at a later date by freezing eggs
rather than embryos," he added.
Kuwayama and his team froze 111 eggs and successfully
thawed 94.5 percent of them using their Cryotop method. They
achieved a pregnancy rate of 41.9 percent following in-vitro
fertilization (IVF), compared to 42.5 percent with fresh eggs.
"The Cryotop method is very efficient," he added.
The technique could allow young cancer patients to freeze
their eggs before having treatments which could damage their
Career women who want to delay having children could also
freeze their eggs for use in fertility treatments at a later
date. But fertility experts advise women not to delay pregnancy
until it may be too late.
A woman's fertility declines rapidly after the age of 35
until she reaches the menopause, which usually occurs around
The new technique involves freezing the egg very rapidly in
a tiny amount of a special solution before it is stored in
liquid nitrogen. Kuwayama said it prevents ice crystals, which
can damage the structure of the egg, from forming.
Professor Arne Sunde, a former chairman of the European
Society of Human Reproduction and Embryology (ESHRE), said
until now freezing human eggs, which is known as
cryopreservation, has been difficult and only 50 percent
With the new method it has risen to 90 percent, he added.
"This is a major improvement, and for the first time,
cryopreservation of oocytes (eggs) represent a realistic option
for the preservation of fertility in women who are in need of
aggressive treatment for malignant diseases," Sunde said.
Nearly 6,000 scientists, researchers and fertility experts
are attending the 4-day ESHRE meeting.