Barcelona, Spain: Children born after a frozen, thawed embryo has been replaced in the womb have higher birth weight than those born where fresh embryos were used, Danish scientists reported to the 24th annual conference of the European Society of Human Reproduction and Embryology today (Tuesday 8 July). The mothers had longer pregnancies, and the children did not show an increased risk of congenital malformations, said Dr. Anja Pinborg, from the Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark.
One possible explanation: freezing of the embryos somehow changes the epigenetic state of the embryos in a way that stimulates growth. I think that explanation unlikely though. The fact that the pregnancies from frozen embryos lasted longer explains at least part of the higher birth weights. But why the longer pregnancies?
The scientists studied all the 1267 children born in Denmark between 1995 and 2006 after frozen embryo replacement (FER). The children were divided into three groups; those born after cryo-preserved IVF (878), those born after cryo-preserved ICSI (310), and 79 where the method of creation of the embryos was unknown. During the same period 17857 children were born after IVF/ICSI treatment using fresh embryos, and these children were used as controls. Data on the children's outcomes, including congenital malformations, were obtained from Danish national registries.
The fact that freezing reduces the need for women to undergo additional hormonal therapies to produce more eggs suggests some other explanations. First off, a woman who receives a thawed embryo is further past the time when her body received the egg release stimulating hormones. That might make a difference in her metabolism where her body starts out the pregnancy in a less stressed out state. Maybe that allows the pregnancy to go longer.
Freezing embryos allows couples to have several cycles of IVF/ICSI from the same egg collection. The embryos are subsequently thawed and replaced three to five days after ovulation in exactly the same way as fresh embryos are used. The technique helps to reduce the number of times ovaries are stimulated and eggs collected.
The fact that the ovaries get stimulated in later attempts with the no-freeze approach might mean that the eggs from the later cycles are more tired. The eggs from the first cycle might be healthier. Again, I'm speculating.
The scientists found similar rates of multiple pregnancies in the FER groups (ICSI 11.7% and IVF 14.2%), but in the fresh embryo groups the rates were considerably higher (ICSI 24.8% and IVF 27.3%). Maternal age was significantly higher in the FER group. Pregnancy duration was significantly longer for these mothers, and birth weight was also higher – about 200 grams – in the FER group. The proportion of low birth weight FER children significantly lower, as was the percentage of pre-term births.
The frozen embryo replacement (FER) group had fewer neonatal ICU admissions.
"Additionally there were significantly fewer children admitted to a neonatal intensive care unit in the FER group," said Dr. Pinborg, "although, when limited to single births, this difference disappeared. Most encouragingly, we found no increased risk of congenital malformations in the FER group; the rate in this group was 7.1% compared to 8.8% where fresh embryos had been used."
When cheap DNA testing technologies can tell us many things about the genetic characteristics of each embryo the motivation for using frozen embryos will go down. Most prospective parents will compare the genetic profiles of a dozen embryos and decide they want one or two of them way more than the rest of them. They might still freeze the embryos not implanted on the first attempt. But if the first embryo implantation attempt does not lead to a pregnancy they'll be motivated to try to create some new embryos in hopes of getting genetic profiles more to their liking.
Frozen eggs strike me as more interesting than frozen embryos. If frozen eggs can be stored for long periods without complications their storage could become popular. A woman in late her teens will be able to freeze young eggs years before she meets Mr. Right. Then in her 30s those frozen eggs will serve as an insurance policy in case the eggs remaining in her ovaries get too old.
Frozen eggs might create a much bigger impact on future human evolution than frozen embryos because the ability to freeze eggs could create a much bigger egg donor market. Egg customers will no longer be limited to only those eggs from women willing to sell at a given moment. Similarly, sellers will be able to bank some eggs and wait for customers to come along who are willing to meet their price. A seller could bank some eggs into a repository freezer when it is convenient. A college student woman won't need to turn down a prospective customer just because it is mid-terms or finals time. Harvest the eggs after finals and they'll be available for sale for months and years to come.
As DNA testing results become more powerful egg donors with sought after genetic profiles will find that banking lots of frozen eggs very profitable. I expect top egg donor prices to rise from the current tens of thousands of dollars to hundreds of thousands of dollars. Women with the right looks, intelligence, personality, and low health risks will be able to sell egg for much more when their genetic profiles show they offer much higher odds for giving prospects parents what they want in their children.
|Share |||Randall Parker, 2008 July 15 10:27 PM Biotech Reproduction|