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演讲者：Nassim Assefi and Brian A. Levine

演讲题目: How in vitro fertilization (IVF) works

In 1978, Louise Brown became the worlds first baby to be born by in vitro fertilization, or IVF. Her birth revolutionized the field of reproductive medicine. Given that approximately one in eight heterosexual couples has difficulty conceiving, and that homosexual couples and single parents often need clinical help to make a baby, the demand for IVF has been growing. IVF is so common, that more than 5 million babies have been born through this technology.

1978年，路易丝·布朗成为世界上第一个通过体外受精（IVF）出生的婴儿。她的出生彻底改变了生殖医学领域。考虑到大约八分之一的异性恋夫妇怀孕困难，而且同性恋夫妇和单亲父母通常需要临床帮助才能生育，体外受精的需求一直在增长。体外受精非常普遍，通过这项技术已经有500多万婴儿出生。

IVF works by mimicking the brilliant design of sexual reproduction. In order to understand IVF, we first need to take a look at the natural process of baby making. Believe it or not, it all starts in the brain. Roughly fifteen days before fertilization can happen, the anterior pituitary gland secretes follicle stimulating hormone, FSH, which ripens a handful of follicles of the ovary that then release estrogen.

体外受精的工作原理是模仿有性生殖的卓越设计。为了理解试管婴儿，我们首先需要了解一下婴儿生育的自然过程。信不信由你，一切都是从大脑开始的。大约在受精前15天，垂体前叶分泌促卵泡激素FSH，FSH使卵巢的一小部分卵泡成熟，然后释放雌激素。

Each follicle contains one egg, and on average, only one follicle becomes fully mature. As it grows and continues to release estrogen, this hormone not only helps coordinate growth and preparation of the uterus, it also communicates to the brain how well the follicle is developing. When the estrogen level is high enough, the anterior pituitary releases a surge of luteinizing hormone, LH, which triggers ovulation and causes the follicle to rupture and release the egg.

每个卵泡包含一个卵子，平均只有一个卵泡完全成熟。随着卵泡的生长并持续释放雌激素，这种激素不仅有助于协调子宫的生长和准备，还可以向大脑传达卵泡的发育情况。当雌激素水平足够高时，垂体前叶会释放大量的促黄体生成素（LH），从而触发排卵，导致卵泡破裂并释放卵子。

Once the egg leaves the ovary, it is directed into the Fallopian tube by the finger-like fimbriae. If the egg is not fertilized by sperm within 24 hours, the unfertilized egg will die, and the entire system will reset itself, preparing to create a new egg and uterine lining the following month.

一旦卵子离开卵巢，它就会被手指状的菌毛引导进入输卵管。如果卵子在24小时内未被精子受精，未受精的卵子将死亡，整个系统将自行复位，准备在下个月产生新卵子和子宫内膜。

The egg is the largest cell in the body and is protected by a thick, extracellular shell of sugar and protein called the zona pellucida. The zona thwarts the entry and fusion of more than one sperm, the smallest cell in the body.

卵子是人体内最大的细胞，由一层厚厚的、由糖和蛋白质组成的细胞外外壳（称为透明带）保护。透明带阻碍了不止一个精子的进入和融合，精子是身体中最小的细胞。

It takes a man two to three months to make sperm, and the process constantly renews. Each ejaculation during sexual intercourse releases more than 100 million sperm. But only 100 or so will ultimately make it to the proximity of the egg, and only one will successfully penetrate through the armor of the zona pellucida.

一个男人需要两到三个月的时间来制造精子，而且这个过程不断更新。性交过程中每次射精都会释放出1亿多精子。但最终只有100个左右能够接近卵细胞，只有一个能够成功穿透透明带的盔甲。

Upon successful fertilization, the zygote immediately begins developing into an embryo, and takes about three days to reach the uterus. There, it requires another three or so days to implant firmly into the endometrium, the inner lining of the uterus. Once implanted, the cells that are to become the placenta secrete a hormone that signals to the ovulated follicle that there is a pregnancy in the uterus.

受精成功后，受精卵立即开始发育成胚胎，大约需要三天时间到达子宫。在那里，还需要三天左右的时间才能牢固地植入子宫内膜，即子宫内膜。一旦植入，将成为胎盘的细胞分泌一种激素，向排卵卵泡发出信号，表明子宫中有妊娠。

This helps rescue that follicle, now called the corpus luteum, from degenerating as it normally would do in that stage of the menstrual cycle. The corpus luteum is responsible for producing the progesterone required to maintain the pregnancy until six to seven weeks of gestation, when the placenta develops and takes over, until the baby is born approximately 40 weeks later.

这有助于挽救卵泡，现在称为黄体，从退化，因为它通常会在该阶段的月经周期。黄体负责产生维持妊娠所需的孕酮，直到妊娠6至7周，胎盘发育并接管，直到大约40周后婴儿出生。

Now, how do you make a baby in a lab? In patients undergoing IVF, FSH is administered at levels that are higher than naturally occuring to cause a controlled overstimulation of the ovaries so that they ultimately produce multiple eggs. The eggs are then retrieved just before ovulation would occur, while the woman is under anesthesia, through an aspirating needle that is guided by ultrasound. Most sperm samples are produced by masturbation.

现在，你如何在实验室里制造婴儿？在接受IVF的患者中，FSH的使用水平高于自然发生的水平，从而导致卵巢的受控过度刺激，从而最终产生多个卵子。在妇女处于麻醉状态时，通过超声波引导的抽吸针在排卵前取出卵子。大多数精子样本是通过自慰产生的。

In the laboratory, the identified eggs are stripped of surrounding cells and prepared for fertilization in a petri dish. Fertilization can occur by one of two techniques. In the first, the eggs are incubated with thousands of sperm and fertilization occurs naturally over a few hours. The second technique maximizes certainty of fertilization by using a needle to place a single sperm inside the egg. This is particularly useful when there is a problem with the quality of the sperm.

在实验室中，将已鉴定的卵子从周围的细胞中剥离出来，准备在皮氏培养皿中受精。受精可以通过两种技术之一进行。首先，卵子与成千上万的精子一起孵化，在几个小时内自然受精。第二种技术通过使用针头将单个精子放入卵子中，最大限度地提高受精的可靠性。当精子质量出现问题时，这一点特别有用。

After fertilization, embryos can be further screened for genetic suitability, frozen for later attempted pregnancies, or delivered into the womans uterus via catheter. Common convention is to transfer the embryo three days after fertilization, when the embryo has eight cells, or on day five, when the embryo is called a blastocyst, and has hundreds of cells.

受精后，可以进一步筛选胚胎的遗传适合性，冷冻以备以后尝试怀孕，或通过导管将其送入女性子宫。通常的做法是在受精后三天移植胚胎，此时胚胎有八个细胞，或者在第五天移植胚胎，此时胚胎被称为胚泡，并且有数百个细胞。

If the womans eggs are of poor quality due to age or toxic exposures, or have been removed due to cancer, donor eggs may be used. In the case that the intended mother has a problematic uterus, or lacks one, another woman, called the gestational carrier or surrogate, can use her uterus to carry the pregnancy.

如果妇女的卵子因年龄或接触有毒物质而质量较差，或因癌症而被取出，可以使用捐赠卵子。如果计划生育的母亲有问题的子宫，或缺少子宫，另一名妇女，称为妊娠携带者或代孕者，可以使用她的子宫进行妊娠。

To increase the odds of success, which are as high as 40% for a woman younger than 35, doctors sometimes transfer multiple embryos at once, which is why IVF results in twins and triplets more often than natural pregnancies. However, most clinics seek to minimize the chances of multiple pregnancies, as they are riskier for mothers and babies.

为了提高成功的几率（35岁以下的女性成功率高达40%），医生有时会同时移植多个胚胎，这就是为什么IVF比自然怀孕更容易产生双胞胎和三胞胎的原因。然而，大多数诊所寻求将多胎妊娠的机会降至最低，因为多胎妊娠对母亲和婴儿的风险更大。

Millions of babies, like Louise Brown, have been born from IVF and have had normal, healthy lives. The long-term health consequences of ovarian stimulation with IVF medicines are less clear, though so far, IVF seems safe for women. Because of better genetic testing, delayed childbearing, increased accessibility and diminishing cost, its not inconceivable that artificial baby making via IVF and related techniques could outpace natural reproduction in years to come.

数以百万计的婴儿，如路易丝·布朗，通过体外受精出生，过着正常、健康的生活。体外受精药物刺激卵巢的长期健康后果尚不清楚，尽管到目前为止，体外受精似乎对女性是安全的。由于更好的基因检测、推迟生育、增加可及性和降低成本，通过体外受精和相关技术制造人工婴儿在未来几年可能会超过自然繁殖，这并非不可想象。

Remark：一切权益归TED所有，更多TED相关信息可至官网www.ted.com查询！

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