卵子冷冻的秘密

对于有生殖问题的女性而言，并不是完全没有希望再次受孕。她们可以通过卵子冷冻程序尝试受孕。Bridge Clinic诊所的临床生殖医生Emmanuel Owie博士介绍了该项技术的相关知识。

年龄或更年期对于想要受孕的女性而言可能不再是一个障碍。由于卵母细胞冷冻保存技术已被广泛采用，女性可以在适当的时候将体内的卵子取出、冷冻并且储存直到她觉得想要怀孕的那一天。冷冻后的卵子可以重新被解冻、受精并被移植回子宫。在低于零度的储存环境中，冷冻的卵细胞或者胚胎细胞将停止几乎所有的生物活动，并能够长期保留以备未来之需。

Bridge Clinic诊所的临床生殖医生Emmanuel Owie博士指出，卵子冷冻技术可以巧妙地绕过女性体内随时都在运行的生物钟。因为当女性年龄增长时，更容易产生卵子染色体异常，并可能使她们怀孕和足月妊娠变得困难。“但有了卵子冷冻的技术手段，在低于零度的储存温度下，冷冻的卵子细胞或者胚胎组织将停止几乎所有的生物进程，从而增加女性在未来成功受孕的机会。人卵母细胞冷冻技术是一种提取、冷冻和储存卵子的过程。当采取了卵子冷冻技术的女性在未来准备怀孕时，可以解冻卵子并使其正常受精，再将胚胎移植到子宫内”，Owie博士说，“此外，对于在化疗期间有可能失去生育能力的女性癌症患者而言，我们特别推荐采用卵子冷冻技术。对于那些有早期绝经家族病史的女性，或者由于宗教或道德的原因反对储存冷冻胚胎的妇女以及想要推迟生育的女性而言，卵子冷冻也是一个不错的选择。我们诊所的卵子冷冻技术采用了尖端的玻璃化冷冻技术，这一技术也被称为“快速卵子冷冻技术”。在采用玻璃化冷冻技术时，卵子或卵母细胞被脱水，而且在冷冻前卵子内残留的水份会被“防冻”溶液（DMSO）代替。这可以防止冰晶的形成，而冰晶会破坏细胞。”

卵子冷冻技术的原理其实很简单，与精子或者胚胎冷冻的原理相同。但是虽然精子和胚胎都很容易被冷冻，而卵子因为是人体内最大的细胞，含有大量的水成份，因此在冷冻过程中，冰晶很容易形成并破坏卵细胞。因此在卵子冷冻过程中，卵子必须经过脱水，并且用DMSO替换卵子内残余水份以防止冰晶的形成。此外，因为卵子细胞膜会在冷冻过程中变硬，因此必须使用标准的浆内单精子注射技术（ICSI卵胞）将精子注射到卵子内以便让其受精。为了获取卵子以便冷冻，患者在取卵之前会接受与其它IVF疗法相同的激素促排卵疗程。与胚胎冷冻技术唯一的区别就是患者的卵子在受精之前便被直接储存到冷冻环境中。

当被问到女性何时应该冷冻她的卵子时，Owie博士说如果女性采用她20多岁或30岁出头时的卵子进行冷冻，其在以后成功怀孕的机会将更大。由于和胚胎冷冻类似，卵子是零下196摄氏度进行冷冻保存，因此它的保存时间可长达十年以上，而且长期储存的冷冻卵子不会有任何质量上的下降。至于女性进行卵子冷冻时需要保存几个卵子，Owie博士说，根据研究，女性一直到38岁之前，其冷冻卵子成功解冻的百分率为75%，而成功解冻后的卵子成功受精率也为75%。因此，如果选择冷冻10个卵子，则预计其中七个能够成功解冻，而这10个卵子中应该有五至六个卵子可以成功受精并发育成胚胎。由于在一个IVF周期内通常有3至4个胚胎被植入患者体内。因此，当女性在38岁之前进行卵子冷冻时，应该为未来每次受孕尝试储存10个卵子。

Fertility: How egg freezing method works, by expert

For fertility challenged women, all hope is not lost.They can become pregnant through the oocyte (egg) freezing producure, which is now available in the country. The Bridge Clinic used the process to deliver a baby on February 16. A fertility physician with the clinic, Dr Emmanuel Owie, takes OYEYEMI GBENGA-MUSTAPHA, through the producure’s rudiments.

Age or menopause may no longer be a barrier to a woman having a child, thanks to oocyte cryopreservation, which is available in the country. Human oocyte cryopreservation (egg freezing) is a process where a woman’s eggs (oocytes) are extracted, frozen and stored to be used when she is ready to become pregnant.The ‘frozen’ eggs can be thawed, fertilised, and transferred to the uterus as embryos. The cooling of cells and tissues to sub-zero temperatures stops all biological activities and preserves the eggs for future use.

The Bridge Clinic is the first fertility clinic to record the feat in the country. A male child, Tiwatope, was delivered in the clinic on February 16, through the process.

According to Dr Emmanuel Owie, a Fertility Physician with the Bridge Clinic, egg freezing is a way of “thwarting” the ticking biological clock’ of women, who when they grow older, are more likely to produce eggs that will have chromosomal abnormalities that can make it harder for them to conceive and carry pregnancies to term.

“But with Cryopreservation, which is the cooling of cells and tissues to sub-zero temperatures in order to stop all biological activities and then preserve the eggs from future use, a woman’s chances at child bearing, is increased. Human oocyte cryopreservation (egg freezing) is a process in which a woman’s eggs (oocytes) are extracted, frozen and stored. Later, when she is ready to become pregnant, the eggs can be thawed, fertilised, and transferred to the uterus as embryos,” said Dr Owie

He said “egg freezing is particularly recommended for the women diagnosed with cancer that may lose their fertility during chemotherapy, women with a family history of early menopause, women with objections to storing frozen embryos for religious and/or moral reasons and women who want or need to delay childbearing in order to pursue some personal goals such as career building”.

Explaining the procedure, using the clinic’s Tiwatope’s accomplishment, Dr Owie said the baby’s birth is significant in many respects, as it has put the country on the global map as regards the practice of oocyte cryopreservation; a new offering in the in-vitro fertilisation (IVF) space.

He said: “Before Tiwa’s birth this new practice seemed to be an exclusive preserve of the developed world of Europe and North America. It is even more significant, considering the fact that since the report of the first pregnancy through this protocol in 1986, the practice has resulted in the birth of only about 5,000 babies worldwide. And Nigeria has added  one with Tiwa’s birth.

“Tiwatope’s mother had her eggs frozen using the vitrification, also known as flash-freezing, process. This is the cutting edge technology in cryobiology, where the eggs or oocytes of a woman is dehydrated and the water content is replaced with ”anti-freeze” solution (cryoprotectants) before freezing. This prevents the formation of ice crystals, which could destroy the cell.”

Tiwa’s parents had battled infertility for eight years, but had the mother had her eggs frozen for two months and on her readiness for pregnancy.

“We fertilised the eggs, using a standard technique known as intracytoplasmic sperm injection (ICSI) in order to overcome the egg shell, which normally gets hardened with freezing. The fertilised egg was subsequently transferred into her womb, resulting in the conception of Tiwa,” “She had her ante natal care in her family hospital and delivered the baby boy through caesarian section (SC),” Dr Owie added.

Explaining the process further, Dr Owie said: “Egg freezing works in a simple way. Though basically sperm and embryos have proved easy to freeze, the egg is the largest cell in the human body and contains a large amount of water. When frozen, ice crystals form that can destroy the cell. We must dehydrate the egg and replace the water with an “anti-freeze” (cryoprotectants) prior to freezing in order to prevent ice crystal formation. We also learned that because the shell of the egg hardens when frozen, sperm must be injected with a needle to fertilise the egg, using a standard technique known as ICSI (Intracytoplasmic Sperm Injection).

“And in order to retrieve eggs for freezing, a patient undergoes the same hormone-injection process as in-vitro fertilization (IVF). The only difference is that following egg retrieval, they are frozen for a period of time before they are thawed, fertilised and transferred to the uterus as embryos.”

Asked when a woman should freeze her eggs, Dr Owie said the chances for success (pregnancy) are greater if a woman uses ‘younger’ eggs—meaning either eggs she froze in her 20s or early 30s, rather than later on. And for how long can the eggs remain frozen? He said eggs are frozen in the same manner as embryos, utilising a freezing temperature of -196 degrees Celsius. Eggs could be preserved for more than ten years. Long-term storage of frozen eggs does not result in any decrease in quality. And how many eggs should a woman store to achieve pregnancy? He said, based on studies, egg thaw rates of 75 per cent and fertilisation rates of 75 per cent are anticipated in women up to 38 years of age. Thus, if 10 eggs are frozen, seven are expected to survive the thaw, and five to six are expected to fertilise and become embryos. Usually three to four embryos are transferred in women up to 38 years of age. It is recommended that 10 eggs be stored for each pregnancy attempt.

Coordinator, Corporate Marketing/Communication and Client Relations, The Bridge Clinic, Dr Ekundayo Omogbehin said aspiring women can be rest assured that the babies born through this medium are normal, as the case of Tiwa has shown, “The baby and the mother are in good health to the delight of the family and friends. We could not put faces (photos of them) to the names due to the sensitivity that still goes with novel developments like IVF, understandably. They have, however, given us permission to use the real name of the baby boy (not surname) as well as the photographs of the new baby.

“We hope these will suffice in the given circumstances. We also hope that, one day, Tiwa’s parents will overcome these sensitivities and come out to encourage other women, who may be in need of this offering to come for it,” he said, adding that the costs for egg freezing are identical to those of routine IVF.

（文章转自沈阳九州医院官方网站）

作者： OYEYEMI GBENGA-MUSTAPHA

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