Posts Tagged ‘frozen embryos’

Freezing Embryos May Result in Healthier IVF Babies

More evidence that using frozen embryos may result in healthier IVF babies than using fresh embryos comes from a new British study.

The researchers found that babies born following IVF using frozen embryos may be born later and weigh more than babies born from fresh embryos, according to a presentation at the British Fertility Society last week.

They looked at nearly 400 babies born after fresh embryo transfer and just more than 100 born after frozen embryo transfer.

On average, babies born from frozen embryos weighed 253g more and were born 4 to 5 days later than babies born from fresh embryos.

“This is important because prematurity and low birth weight are both risk factors for poorer health later in life and are linked to higher rates of behavioral and learning difficulties,” said Suzanne Cawood, who led the study at the Centre for Reproductive and Genetic Health in London.

“This means that resulting babies may potentially be healthier if frozen embryos are transferred rather than fresh embryos.”

She hypothesizes that the difference may be in the uterine environment between fresh cycles when embryos are transferred soon after the eggs have been collected compared to frozen cycles when the uterus has not been stimulated in the days before transfer.

This hypothesis needs to be tested further, she said.

Previously, Danish scientists had found that babies from frozen embryos were heavier and suggested this could be due to only top quality embryos surviving the freezing procedure.

Early-stage Thawed Frozen Embryos Lead to Fewer Miscarriages

Most IVF clinics have embraced freezing embryos as a way to enhance a couple’s chances of achieving a pregnancy.

Better ovulation induction protocols now allow the harvesting of 10 or more mature eggs from a woman from one cycle of hormonal stimulation.

Freezing embryos allows couples to have several IVF treatment cycles from the same egg collection, reducing the number of times that the ovaries are stimulated and, therefore, reducing the costs.

The most costly part of an IVF cycle is the ovulation induction, egg retrieval, and fertilization stages.

Frozen embryos can also be used during a natural cycle IVF without any hormonal stimulation.

Natural cycle replacement is an easier procedure, and is usually recommended for a woman who ovulates regularly and normally.

Thawed Embryo Transfer

The thawed embryos are placed into the uterus three to five days after ovulation in exactly the same way as fresh embryos.

The transfer is timed to the stage of development of the embryo.

Embryos frozen at the 8-cell stage are transferred earlier than those frozen at the blastocyst stage.

For a natural cycle, the fertility team will thaw earlier embryos one day after ovulation (two days after the LH peak) and make the transfer on the day of the thaw.

Blastocysts are thawed five days after the LH peak and transferred on the day of the thaw.

About 75% of frozen embryos survive the thawing at Weill Cornell in New York, says Zev Rosenwaks, MD, director and physician-in-chief of the Center for Reproductive Medicine at the Weill Cornell Medical Center.

“Our pregnancy rates are slightly higher – more than 50% – when blastocysts are thawed and transferred compared to earlier stage embryos.”

A new study in the December issue of Reproductive BioMedicine Online (www.rbmonline.com) states that miscarriage is less likely to occur after the transfer of fresh embryos compared with frozen-thawed embryos, but also that the age of the embryos at the time of freezing could influence the miscarriage rate.

The retrospective analysis of more than 52,000 clinical pregnancies recorded on the Australian and New Zealand Assisted Reproduction Database between 2004 and 2008 showed that a woman’s age and obstetric history are closely related to the risk of miscarriage, but that the transfer of fresh embryos is associated with fewer miscarriages than transfer of frozen–thawed embryos.

Transferring thawed embryos at an earlier stage of development than the blastocyst stage reduced the likelihood of miscarriage, leading the authors to suggest that transferring fresh blastocysts and freezing of cleavage-stage embryos might reduce miscarriage rates.

However, a retrospective analysis of large national databases is mainly useful to identify trends and generate hypothesis.

“It is interesting that miscarriage rates of frozen blastocysts were higher in the Australian study, particularly since it is well known that blastocysts have a lower frequency of chromosomal anomalies than cleaved embryos,” said Dr. Jacques Cohen, senior editor of Reproductive BioMedicine Online, of the study.

“Blastocyst culture is still a relatively new approach and culture-related factors such as selection for freezing at blastocyst stage may have affected early learning experiences in some clinics.

It is therefore important to repeat a similar analysis of Australian clinic data during subsequent years.”

Frozen Embryos Healthier

Initially, there were some concerns about the health of children born to women who had frozen embryos transfers, but now we know these children are just as normal as those conceived with fresh embryos.

There’s even some evidence that frozen embryos are healthier than fresh embryos.

A Danish study found that women implanted with frozen embryos had babies who weighed slightly more than those implanted with fresh embryos, and they also had fewer multiple births.

The reason for the differences is probably that only top-quality embryos survive the freezing and thawing process, allowing the selection of healthier embryos.