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  • In 1978, Louise Brown became

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

  • Her birth revolutionized the field of reproductive medicine.

  • Given that approximately 1 in 8 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.

  • 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 15 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.

  • 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.

  • 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.

  • 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.

  • It takes a man 2 to 3 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.

  • Upon successful fertilization,

  • the zygote immediately begins developing into an embryo,

  • and takes about 3 days to reach the uterus.

  • There, it requires another 3 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.

  • 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 6 to 7 weeks of gestation,

  • when the placenta develops and takes over,

  • until the baby is born approximately 40 weeks later.

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

  • In patients undergoing IVF, FSH is administered at levels that are higher than naturally occurring 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.

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

  • and prepared for fertilization in a petri dish.

  • Fertilization can occur by 1 of 2 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.

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

  • frozen for later attempted pregnancies,

  • or delivered into the woman's uterus via catheter.

  • Common convention is to transfer the embryo 3 days after fertilization, when the embryo has 8 cells, or on day 5, when the embryo is called a blastocyst, and has hundreds of cells.

  • If the woman's 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.

  • 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.

  • 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,

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

  • could outpace natural reproduction in years to come.

In 1978, Louise Brown became

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C1 高級 中文 TED-Ed 寶寶 實驗室 製造 番茄 番紅花

TED-Ed】如何製造一個嬰兒(在實驗室裡)--納西姆-阿塞菲和布萊恩-A-萊文。 (【TED-Ed】How to make a baby (in a lab) - Nassim Assefi and Brian A. Levine)

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    稲葉白兎 發佈於 2021 年 01 月 14 日
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