How in vitro fertilization (IVF) works - Nassim Assefi and Brian A. Levine

翻译人员: Jin Wu 校对人员: Mengyu Zheng

In 1978, Louise Brown became

1978年 路易斯·布朗 成为世界上第一个

the world's first baby to be born by in vitro fertilization, or IVF.

通过体外受精 诞生的婴儿 即试管婴儿

Her birth revolutionized the field of reproductive medicine.

他的诞生革新了生殖医学领域

Given that approximately one in eight heterosexual couples

由于大概八分之一的异性恋夫妇

has difficulty conceiving,

会遭遇受孕困难

and that homosexual couples and single parents

以及同性伴侣和单身父/母亲

often need clinical help to make a baby,

通常都需要医学帮助来生宝宝

the demand for IVF has been growing.

对试管婴儿的需求一直在增长

IVF is so common, that more than 5 million babies have been born through this technology.

试管婴儿已经常见到 超过五百万的婴儿由此诞生

IVF works by mimicking the brilliant design of sexual reproduction.

试管婴儿技术模拟了 有性繁殖的高明设计

In order to understand IVF,

为了理解什么是试管婴儿技术

we first need to take a look at the natural process of baby making.

我们首先需要看一下 自然的婴儿诞生过程

Believe it or not, it all starts in the brain.

无论你信不信， 一切都是从大脑开始的

Roughly fifteen days before fertilization can happen,

大概在可以受孕的十五天前

the anterior pituitary gland secretes follicle stimulating hormone, FSH,

脑垂体前叶腺体 会分泌促卵泡激素 FSH

which ripens a handful of follicles of the ovary

它会使卵巢内壁的几个卵泡成熟

that then release estrogen.

然后卵泡会分泌雌性激素

Each follicle contains one egg,

每个卵泡中含有一个卵子

and on average, only one follicle becomes fully mature.

通常而言 只会有一个卵泡充分成熟

As it grows and continues to release estrogen,

随着卵泡的成长并持续 释放雌性激素

this hormone not only helps coordinate growth and preparation of the uterus,

这种激素不仅有助于 协调子宫的生长和预备

it also communicates to the brain how well the follicle is developing.

还会与大脑沟通 卵泡的发展状况如何

When the estrogen level is high enough,

当雌性激素的水平足够高

the anterior pituitary releases a surge of luteinizing hormone, LH,

脑垂体前叶会急剧释放 大量促黄体生成激素 LH

which triggers ovulation

这种激素会触发排卵

and causes the follicle to rupture and release the egg.

导致卵泡破裂并释放卵子

Once the egg leaves the ovary,

卵子一旦离开卵巢

it is directed into the Fallopian tube by the finger-like fimbriae.

就会被手指状的纤毛导入输卵管

If the egg is not fertilized by sperm within 24 hours,

如果卵子没有在二十四小时之内受精

the unfertilized egg will die,

未受精的卵子会消亡

and the entire system will reset itself,

然后整个系统会恢复原状

preparing to create a new egg and uterine lining the following month.

准备好在下个月产生 一个新的卵子和子宫内膜

The egg is the largest cell in the body

卵子是身体内最大的细胞

and is protected by a thick, extracellular shell of sugar

由一个厚厚的、糖和 蛋白质构成的细胞外壳保护

and protein called the zona pellucida.

这层细胞外壳叫做透明带

The zona thwarts the entry and fusion of more than one sperm,

透明带阻隔超出一个的 多余精子进入，并将其融化

the smallest cell in the body.

而精子是身体内最小的细胞

It takes a man two to three months to make sperm,

男人需要两到三个月 来生成精子

and the process constantly renews.

这个过程不断持续更新

Each ejaculation during sexual intercourse releases more than 100 million sperm.

性交过程中的每次射精 会释放超过一亿个精子

But only 100 or so will ultimately make it to the proximity of the egg,

但是只有一百个左右 会最终接近卵子

and only one will successfully penetrate through the armor of the zona pellucida.

而且只有一颗精子能够 成功的穿透透明带的铠甲

Upon successful fertilization,

一旦受精成功

the zygote immediately begins developing into an embryo,

受精卵即刻开始发育成胚胎

and takes about three days to reach the uterus.

然后大概要用三天的时间抵达子宫

There, it requires another three or so days

在这里，它还需要大约三天时间

to implant firmly into the endometrium, the inner lining of the uterus.

才能牢固的在宫内膜 即子宫内膜上着床

Once implanted, the cells that are to become the placenta

一旦着床 未来变成胎盘的细胞

secrete a hormone that signals to the ovulated follicle

会释放激素来通知卵泡

that there is a pregnancy in the uterus.

子宫内已经有了受精卵

This helps rescue that follicle, now called the corpus luteum,

这会使得卵泡，现在称为黄体

from degenerating as it normally would do in that stage of the menstrual cycle.

免于像往常一样在月经 周期的某个阶段退化

The corpus luteum is responsible for producing the progesterone

黄体负责产生孕酮

required to maintain the pregnancy until six to seven weeks of gestation,

而孕酮可以维持孕期 到六至七个星期

when the placenta develops and takes over,

这时候胎盘会发育好并接管 孕期的维持

until the baby is born approximately 40 weeks later.

一直到大概40周后婴儿出生

Now, how do you make a baby in a lab?

那么在实验室里如何培养婴儿呢？

In patients undergoing IVF,

进行体外受精的病人

FSH is administered at levels that are higher than naturally occuring

会被给予高于自然水平的 卵泡刺激素

to cause a controlled overstimulation of the ovaries

来保持对于卵巢的可控过度刺激

so that they ultimately produce multiple eggs.

从而最终产生多个卵子

The eggs are then retrieved just before ovulation would occur,

在排卵发生之前这些卵子

while the woman is under anesthesia,

会在母体麻醉的状态下

through an aspirating needle that is guided by ultrasound.

通过由超声波引导的吸针被采集

Most sperm samples are produced by masturbation.

大部分精子样本会通过自慰产生

In the laboratory, the identified eggs are stripped of surrounding cells

在实验室筛选出来的 卵子会剥去细胞外壁

and prepared for fertilization in a petri dish.

在培养皿里等待受精

Fertilization can occur by one of two techniques.

受精可以通过两种技术之一来实现

In the first, the eggs are incubated with thousands of sperm

第一种方法中，卵子会同几千个精子一起培养

and fertilization occurs naturally over a few hours.

在几个小时之内受精会自然发生

The second technique maximizes certainty of fertilization

第二种技术会使得受精的确定性最大化

by using a needle to place a single sperm inside the egg.

这种技术使用探针将单个精子置入卵子内

This is particularly useful when there is a problem with the quality of the sperm.

当精子质量有问题时，这种方式尤其有用

After fertilization, embryos can be further screened for genetic suitability,

受精之后，胚胎可以 继续筛查基因适宜性

frozen for later attempted pregnancies,

可以冷冻用来今后怀孕

or delivered into the woman's uterus via catheter.

也可以直接通过导管置入子宫

Common convention is to transfer the embryo three days after fertilization,

惯常做法是在受精三日之后植入胚胎

when the embryo has eight cells,

这个时候胚胎会有八个细胞

or on day five, when the embryo is called a blastocyst,

或者在第五天植入 这个时候胚胎叫做胚囊

and has hundreds of cells.

已经有了数百个细胞

If the woman's eggs are of poor quality due to age or toxic exposures,

如果女性的卵子因为年龄或者有毒环境接触 而质量不高

or have been removed due to cancer,

或者因为癌症而摘除了卵巢

donor eggs may be used.

则可以使用捐赠的卵子

In the case that the intended mother has a problematic uterus, or lacks one,

如果想要怀孕的母亲子宫 存在问题或者缺失

another woman, called the gestational carrier or surrogate,

另一个女人，作为受孕载体或者代孕者

can use her uterus to carry the pregnancy.

可以用她的子宫来孕育婴儿

To increase the odds of success,

为增加成功几率

which are as high as 40% for a woman younger than 35,

在35岁以下的女性中 会高达40%

doctors sometimes transfer multiple embryos at once,

医生有时候会一次植入多个胚胎

which is why IVF results in twins and triplets

这就是为什么试管婴儿出现 双胞胎或者三胞胎的几率

more often than natural pregnancies.

会远远高于自然怀孕

However, most clinics seek to minimize the chances of multiple pregnancies,

然而大部分诊所都在 试图将多胞胎的几率最小化

as they are riskier for mothers and babies.

因为对于母亲和孩子来说 多胞胎的风险会更高

Millions of babies, like Louise Brown, have been born from IVF

数以百万计的宝宝， 比如路易斯·布朗，通过试管婴儿技术出生

and have had normal, healthy lives.

过着正常健康的生活

The long-term health consequences of ovarian stimulation

关于试管婴儿技术进行卵巢刺激的

with IVF medicines are less clear,

长期健康后果目前还不清晰

though so far, IVF seems safe for women.

尽管直到目前 试管婴儿看起来对女性是安全的

Because of better genetic testing,

因为有更好的基因测试

delayed childbearing,

推迟的分娩，

increased accessibility and diminishing cost,

更高的便捷度和降低的花费

it's not inconceivable that artificial baby making via IVF and related techniques

通过体外受精及相关技术来人工 培育婴儿，在未来可能会超过自然生育

could outpace natural reproduction in years to come.

也不会是多么难以置信的事情