Frozen eggs rival IVF success of fresh eggs

日期:2019-03-02 10:01:06 作者:秘酊涛 阅读:

By Linda Geddes, Prague Women hoping to put their biological clocks on hold by freezing their eggs now stand almost as great a chance of getting pregnant as those using fresh eggs for in vitro fertilisation. Improvements in “cryopreservation” techniques have virtually eliminated the problem of ice crystals forming and causing structural damage to eggs – a major flaw of conventional freeze-thaw techniques. New results show these improvements have resulted in pregnancy rates almost identical to those achieved with IVF using fresh eggs. Masashige Kuwayama of the Kato Ladies Clinic in Tokyo, Japan, developed a technique called Cryotop. It involves snap-freezing eggs in a tiny amount of solution, before storing them in liquid nitrogen. During conventional freeze-thawing, eggs are exposed to protective chemicals and slowly frozen over the course of several hours. Kuwayama froze 111 eggs, of which 94.5% survived subsequent thawing. These were fertilised by intra-cytoplasmic sperm injection and 29 of the resulting embryos were implanted into women. The result was 12 pregnancies – a success rate of 41.9% compared with 42.5% using fresh eggs. Eleven healthy babies were born, including one set of twins, while two of the pregnancies miscarried. The results were presented at the European Society of Human Reproduction and Embryology (ESHRE) conference in Prague, Czech Republic, on Monday. “This is a major improvement, says Arne Sunde, former chairman of ESHRE. “Previously around one child was born for every hundred oocytes cryopreserved, now it is more like 10 children for every hundred. If these results can be replicated by other clinics then cryopreservation of human oocytes may for the first time be a viable option for the preservation of fertility in women.” Conventional freeze-thawing has been used to store human embryos and eggs since the 1980s, but so far only around 150 babies have been born worldwide using eggs that have been frozen. In another development, Italian researchers have shown that eggs can be screened for chromosomal abnormalities that might reduce IVF success rates. A common problem in IVF, particularly in women over 35, is that many of the eggs are “aneuploid” – they contain the wrong number of chromosomes. This can result in birth defects like Down’s syndrome, or embryos that fail to implant or later miscarry. Ana Pia Ferraretti and colleagues at SISMER (Società Italiana Studi di Medicina Della Riproduzione) in Bologna, Italy, analysed chromosomes from the “first polar body” to select healthy eggs with the correct number of chromosomes. The first polar body is a small membrane-bound structure that is expelled from the developing egg during cell division and which contains the same number of chromosomes as the egg. They compared 266 women implanted with embryos created after first polar body analysis (PBA) with a control group of 244 women implanted with eggs whose external appearance was normal. The early miscarriage rate was significantly lower in the PBA group, with 11.5% of women experiencing miscarriage, compared to 28.6% of those in the control group. Performing PBA analysis did not affect fertilisation rates, embryo development or implantation potential,