This might seem hard to believe,
這聽上去令人難以置信，
but right now, 300 million women across the planetare experiencing the same thing: a period.
但是現在全球近3億的女性正在經歷著同樣的事情：一段特殊的時期。
The monthly menstrual cycle that leads to the periodis a reality most women on Earth will go through intheir lives.
這就是每月一次的月經期，是一個全球婦女在她們的一生中必然要面對的現實。
But why is this cycle so universal? And what makes it a cycle in the first place?
但為什麼這個周期如此普遍呢？最開始的周期是怎樣形成的呢？
Periods last anywhere between two and seven days, arising once within in a 28-day rotation.
月經會持續2-7天，每28天循環發生。
That whole system occurs on repeat, happening approximately 450 times during a woman'slife.
月經現象會重複不斷地出現，女人的一生大概會有450次的月經。
Behind the scenes are a series of hormonal controls
表象之下，這一切都是由人體激素進行調控的，
that fine tune the body's internal workings to make menstruation start or stop during those 28 days.
激素精密地控制著身體內部的運作，在這28天裡控制經期的起始。
This inner machinery includes two ovaries stocked with thousands of tiny sacks called follicles
這套內部機制包含兩個卵巢，卵巢內存有成千上萬的微小袋子，叫做卵泡，
that each contain one oocyte, an unfertilized egg cell.
每個卵泡內都含有一個卵母細胞，即未受精卵細胞。
At puberty, ovaries hold over 400 thousand egg cells,
青春期時期，卵巢內含有超過40萬的卵細胞，
but release only one each month, which results in pregnancy or a period.
但每個月只會釋放出一個卵細胞，正是這個卵細胞決定著女性是受孕還是月經。
Here's how this cycle unfolds.
接下來我們來看看這個循環過程是如何產生的。
Each month beginning around puberty,
青春期的每個月初時候，
the hormone-producing pituitary gland in the brain starts releasing two substances into the blood:
大腦中的腦下垂體會分泌激素向血液中釋放兩種物質：
follicle stimulating hormone and luteinizing hormone.
促卵泡激素和黃體化激素。
When they reach the ovaries, they encourage the internal egg cells to grow and mature.
當它們到達卵巢後，會促進子卵巢內卵泡的發育和成熟。
The follicles respond by pumping out estrogen.
卵泡的成熟，會進一步促進雌性激素的分泌。
The egg cells grow and estrogen levels peak, inhibiting the production of FSH, and telling thepituitary to pump out more LH.
伴隨著卵細胞的成長，雌性激素的分泌也將達到峰值，同時抑制促卵泡激素，促進垂體釋放更多的黃體化激素。
That causes only the most mature egg cell from one of the ovaries to burst out of the follicleand through the ovary wall.
結果就是，只有其中一個卵巢中發育最為成熟的卵細胞，才能衝出卵泡，穿越子房壁。
This is called ovulation, and it usually happens ten to sixteen days before the start of a period.
這就是排卵現象，排卵通常發生在月經前的10到16天。
The tiny oocyte moves along the fallopian tube.
微小的卵母細胞沿輸卵管運動。
A pregnancy can only occur if the egg is fertilized by a sperm cell within the next 24 hours.
只有當卵母細胞（卵子）和精子結合後女性才會受孕，這需要在排卵後24小時之內發生。
Otherwise, the egg's escapade ends, and the window for pregnancy closes for that month.
否則，意味著卵子使命的終結，女性在該月受孕的窗口也會關閉。
Meanwhile, the now empty follicle begins to release progesterone,
與此同時，空虛的卵泡開始釋放孕酮，
another hormone that tells the womb's lining to plump up with blood and nutrients
另一種激素以刺激子宮內膜產生血液和營養物質，
in preparation for a fertilized egg that may embed there and grow.
為受精卵的著床和生長做準備。
If it doesn't embed, a few days later, the body's progesterone and estrogen levels plummet,
如果沒有受精卵著床，幾天後，身體的孕酮和雌性激素驟降，
meaning the womb stops padding out and starts to degenerate, eventually falling away.
刺激子宮停止補充養分，內膜開始退化壞死，漸漸脫落。
Blood and tissue leave the body, forming the period.
血液和脫落的子宮內膜離開身體，形成月經。
The womb can take up to a week to clear out its unused contents, after which, the cycle beginsanew.
子宮清理內部無用物質的過程常常會持續一周，之後一個新的周期又開始了。
Soon afterwards, the ovaries begin to secrete estrogen again,
很快，卵巢又開始分泌雌性激素，
and the womb lining thickens, getting ready to accommodate a fertilized egg or be shed.
子宮內膜開始變厚，為受精卵著床最準備或再一次脫落。
Hormones continually control these activities by circulating in ideal amounts delivered at justthe right time.
激素長期控制著整個活動過程，通過在精確的時間輸送理想的量。
The cycle keeps on turning, transforming each day and each week into a milestone along itscourse towards pregnancy or a period.
隨著周期的循環前行，令每一天，每個星期，都是這個受孕或經期過程中的一個裡程碑。
Although this cycle appears to move by clockwork, there's room for variation.
雖然這個過程看上去如時鐘般精準，但它仍然會有區別。
Women and their bodies are unique, after all.
畢竟每位女性及其身體都是獨一無二的。
Menstrual cycles occur at diffferent times in the month,
每個月，月經產生的時間因人而異；
ovulation comes at various points in the cycle, and some periods last longer than others.
排卵期出現的節點不同；甚至經期持續的時間也各有長短。
Menstruation even begins and ends at different times in life for different women, too.
另外，對於不同的女性來說，一生中初潮和絕經的時間也不盡相同。
In other words, variations between periods are normal.
換言之，不同個體的經期有差別是正常的。
Appreciating these differences and learning about this monthly process can empower women,
欣賞這些不同並學習關於生理周期的過程，能讓女性更加的從容自主，
giving them the tools to understand and take charge of their own bodies.
讓女性了解並掌控自己的身體。
That way, they're able to factor this small cycle into a much larger cycle of life.
這樣，她們能夠將從這個小周期領會到的東西，運用在更加複雜的生活周期之中。