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

譯者: Remy Liu 審譯者: Shelley Krishna Tsang

In 1978, Louise Brown became

1978年 路易斯·布朗成為

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

世界上第一位試管嬰兒

Her birth revolutionized the field of reproductive medicine.

她的誕生徹底改變了生殖醫學領域

Given that approximately one in eight heterosexual couples

由于大概八分之一的異性戀夫婦

has difficulty conceiving,

會遭遇受孕困難

and that homosexual couples and single parents

以及同性伴侶和單親父母

often need clinical help to make a baby,

通常都需要醫學幫助來生寶寶

the demand for IVF has been growing.

試管嬰兒的需求一直在增長

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

試管嬰兒已經如此常見

有超過五百多萬嬰兒都透過這項技術誕生

IVF works by mimicking the brilliant design of sexual reproduction.

試管嬰兒技術是模擬傳統的性生殖方式

In order to understand IVF,

為了理解什麼是試管嬰兒技術

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嬰兒製造過程

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

可能難以相信 這一切都是從大腦開始的

Roughly fifteen days before fertilization can happen,

大約受孕前的十五天

the anterior pituitary gland secretes follicle stimulating hormone, FSH,

腦下垂體前葉將釋放促卵泡激素：FSH

which ripens a handful of follicles of the ovary

這會使卵巢內的卵泡變成熟

that then release estrogen.

然後分泌雌激素

Each follicle contains one egg,

每個卵泡內各含一顆卵子

and on average, only one follicle becomes fully mature.

通常而言 只會有一個卵泡發育成熟

As it grows and continues to release estrogen,

隨着卵泡的成長和雌激素的釋放

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

此賀爾蒙不僅有助於協調子宫的生長和預備

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

還會與大腦溝通卵泡的發展狀況

When the estrogen level is high enough,

當雌激素分泌到達高峰時

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

腦垂體前葉會釋放促黄體生成激素：LH

which triggers ovulation

促使排卵

and causes the follicle to rupture and release the egg.

導致卵泡破裂 並釋放卵子

Once the egg leaves the ovary,

卵子一旦離開卵巢

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

就會被手指狀的纖毛導入輸卵管

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

如果卵子没有在二十四小時之内受精

the unfertilized egg will die,

未受精的卵子會自然死亡

and the entire system will reset itself,

整個週期會重新設定

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

做好下個月的新卵子以及子宫内膜的準備

The egg is the largest cell in the body

卵子是體内最大的細胞

and is protected by a thick, extracellular shell of sugar

被糖和蛋白質構成的一種厚厚的

and protein called the zona pellucida.

叫做透明帶的細胞外殼保護

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

透明带阻隔并且融化超出一个的其他精子进入，

the smallest cell in the body.

而精子是体内最小的细胞。

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

生成精子会花费一个男子两到三个月的时间，

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一亿个以上的精子。

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到达卵子近身

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一个胚芽，

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

在哪里，需要另外大概三天时间，

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

会释放荷尔蒙，通知卵泡

that there is a pregnancy in the uterus.

子宫内已经有了身孕

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，而孕酮

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

是使孕期维持并发展到六至七个星期

when the placenta develops and takes over,

这时候胎盘会发育好并接管，

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制造宝宝呢？

In patients undergoing IVF,

进行体外受精的病人体内

FSH is administered at levels that are higher than naturally occuring

卵泡刺激素会控制到高于自然水平，

to cause a controlled overstimulation of the ovaries

来保持对于卵巢的过度刺激

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.

在培养皿里等待受孕。

Fertilization can occur by one of two techniques.

受精可以通过一种或者两种技术来实现，

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

最开始，卵子会同几千个精子一起培养

and fertilization occurs naturally over a few hours.

在几个小时之内受孕会自然发生

The second technique maximizes certainty of fertilization

第二种技术会使得受孕的确定性最大化

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

通过使用探针将单个精子置入卵子

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,

受孕之后，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,

受精三日之后，胚胎会有八个细胞，

when the embryo has eight cells,

这个时候移植是惯常做法。

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

或者在第五天，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,

如果卵子因为年龄或者有毒环境暴露而质量不高时，

or have been removed due to cancer,

或者因为癌症摘除（卵巢），

donor eggs may be used.

可以使用捐赠的卵子。

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

在想要怀孕的母亲子宫有问题，或者子宫缺失的情况下，

another woman, called the gestational carrier or surrogate,

另外的女人，成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。

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,

35岁之前的女性会高达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IVF导致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，大部分诊所都在寻求把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，多胞胎风险会更高。

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

数以百万计的宝宝，就像路易斯·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，IVF似乎对于女性是安全的。

Because of better genetic testing,

因为更好的基因测试，

delayed childbearing,

推后的生子计划，

increased accessibility and diminishing cost,

更高的便捷度和递减的花费，

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制造宝宝，在将来会超过自然生殖，

could outpace natural reproduction in years to come.

也不会是多么难以置信的事情。