Egg freezing is still a relatively new technique that allows eggs to be stored for a long time at temperatures below freezing point. In the UK, 32 centres are licensed by the HFEA to carry out this procedure although fewer than 10 centres offer it to patients at the moment.
Egg freezing can be used successfully for both social and medical reasons. It is becoming more relevant and in demand as many women are facing the real challenge of having successful, healthy pregnancies later in life. This technique offers women planning to have children after the age of 37 the opportunity to effectively slow down their biological clocks by storing their eggs during their reproductive prime. Furthermore, women at risk of premature ovarian failure or those undergoing specific medical treatment that may affect their fertility such as chemotherapy, radiotherapy or surgical removal of the ovaries, may benefit from egg freezing.
The ovarian stimulation protocol is individualised to maximise the chances of success while reducing the risks, complications and possibly the costs of treatment. Daily fertility drugs (hMG or recombinant FSH or recombinant FSH/LH with or without GnRH agonist or antagonist) are necessary to stimulate the ovaries to produce a high number of oocytes (eggs). The recruitment and development of follicles which contain the eggs, is tracked by regular transvaginal ultrasound scans and sometimes blood tests. When at least three follicles are mature (greater than 17mm in diameter) a hormone injection (hCG) is given to ripen the eggs. Egg collection is performed 34-36 hours later. The egg collection procedure takes about 20 minutes. Following egg collection, the eggs can be preserved using either the slow-freeze method or the vitrification method (also known as fast-freeze) before storing them in liquid nitrogen at -196 °C for future use. According to the HFEA eggs can be stored up to a period of 10 years which can be extended only in exceptional circumstances. Not all eggs survive the freezing/thawing process. When required the healthy viable eggs are then fertilised using ICSI.
Egg freezing is still experimental with only a small number of births occuring as a result using this technique in the UK. The live birth rate using frozen eggs is approximately 15%. Data in the literature show that there is no increase in birth defects or chromosomal abnormalities in children born from frozen eggs.
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