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Why can’t women get pregnant without the menstrual cycle? (2016) (quora.com)
488 points by johnny313 on Feb 26, 2018 | hide | past | web | favorite | 111 comments

I first wondered if OP means that first answer with the obscure and horrible programming analogy then I found the real answer by Suzanne Sadedine which is an amazing read.

That was the creepiest part:

Some fetal cells find their way through the placenta and into the mother's bloodstream. They will grow in her blood and organs, and even in her brain, for the rest of her life, making her a genetic chimera

and this is a wonderful summary of evolution:

In other words, it's just the kind of effect natural selection is renowned for: odd, hackish solutions that work to solve proximate problems

I came across this essay a while back titled "War in the Womb" which brings up game game-theory components to the two systems "fighting".


I doubt it's all black and white as you tell it: https://www.newscientist.com/article/dn21185-fetus-donates-s...

If the mother's body leaves fetal cells alone, they have can act as essentially free stem cells, helping repairs.

I forget the exact journal, but women that had like two or three kids, live longer on average than those that didn't.

Perhaps it was this article -- where analysis of age-50+ members of a particular Amish community showed that lifespan of mothers increases linearly up to 14 children, and increases with later age at last birth:


(Interesting... it also shows a positive -- but lower/noisier -- effect for fathers as well, so there may be more at work than just stem cells.)

Just a friendly reminder that correlation != causation. Personally, I would bet that what's happening here is that healthier individuals choose to have more children, rather than that having more children increases life span.


An evolutionary theory based guess is that healthy long lived individuals are more attractive in the mating arena and therefore have more children.

I think the Amish get married young and then stay married for life, so not sure if attractiveness plays a factor (since more or less everybody gets a mate).

> women that had like two or three kids, live longer on average than those that didn't

Can't have 3 kids if you died at age of 10.

While that's true, the context of the statement makes it clear that's not what's being discussed at all.

I assume they looked at groups of women, and controlled for partner presence.

Previously posted here: https://news.ycombinator.com/item?id=8155153

I reposted it before seeing your comment because it has been 4 years. My how time flies.


That is an amazing explanation of primate pregnancy and menstruation. Another extremely creepy aspect is how the placenta burrows into the endometrium.

It sounds a lot like tumor angiogenesis, doesn't it? Indeed, the fetus sounds like the alien ones in Alien. An unwanted fetus is rather like an attacker. Especially in light of conflicting selection pressure.

Awesome and chilling read. I'm so not sharing this with my wife until after we have our second and final baby in a few weeks. ;)

Funny that you should mention tumor angiogenesis. Two of my female friends were diagnosed with Uterine Fibroids [1] in their 30s, and both their doctors said basically the same thing in recommending hysterectomy - paraphrasing:

"The uterus is good for two things, growing babies and growing tumors."

Apparently these are extremely common, and hormonal birth control exacerbates the problem by making the body behave as if it's constantly pregnant. Both of my friends were angry about having been casually prescribed birth control pills as teens without being clearly informed of it increasing the probability of this outcome.

[1] https://en.wikipedia.org/wiki/Uterine_fibroid

On the topic of birth control, your Wikipedia links though says that "The incidence of uterine fibroids in Europe is thought to be lower than the incidence in the US."

Since hormonal birth control is much more common in Europe than in the US, that would seem to hint that uterine fibroids are not directly linked to hormonal birth control.

On the contrary, the pill seems to help prevent them instead[1].

When I lived in Canada I was always surprised how much people seemed to fear the pill when it has been something completely normal in Europe for two generations already. I'm still not sure why there is this difference of attitude between the two sides of the Atlantic.


This is not a topic I have researched one iota. My post was simply sharing what these women shared with me about their experiences with their respective doctors.

However, it takes little effort to find contradictory information on the subject via google:

"Medical practitioners believe and research has recognized the increased levels of estrogen generated by the body preparing for pregnancy and preventative medicines like birth control have a correlation between the cause and effect of uterine fibroids."

"There are two major components known for stimulating the growth of fibroids; estrogen and progesterone. Birth control pills contain both of these elements causing the medical industry to take additional steps in studying the levels of estrogen and the potential rate of fibroid enlargement caused by a women’s use of prescribed birth control pills."

taken from https://fibroids.com/blog/fact-fiction-birth-control-can-cau...

Considering the amount of revenue hormonal birth control generates for pharmaceutical companies, it would not surprise me in the least to discover behaviors resembling the tobacco industry's misinformation campaigns to protect those revenues.

Your blog article does say that under a section called "facts", but it is still nothing more than an unsourced blog with an agenda that might be even more questionable that that of pharmaceutical companies, so I am not going to trust it above a research publication that found birth control pills reduce risk.

Birth control pills are mostly generic and super cheap. The name brand ones are expensive due to the click wheel package.

I assume, perhaps wrongly, that any prescription drug a large swath of the population is taking continously is a cash cow by multiplication alone.

"Global contraceptives market size in 2015 was USD 19.8 billion and is projected to increase at 6.8% CAGR throughout the next seven year timeframe."

"Contraceptive pills is identified to be the most lucrative product segment in the contraceptive drugs market, estimated to grow at a CAGR of 5.3%, from 2016 to 2023. The industry is majorly driven by the presence of favorable government initiatives and regulatory framework."


You are incorrect. I researched DIY HRT for a trans friend of mine. It turns out that in most countries estrogen is so cheap to manufacture, that it is cheaper to manufacture estrogen than it is to replace it with a low-cost alternative. [You can dig https://www.reddit.com/r/TransDIY for sources, this was written from memory]

It's a pure commodity.

I recall when my wife was moved to the generic the out of pocket cost was like $8, which was under the copay. The pharmacist said that the placebo pill that is there for the last days of the cycle was more expensive than the actual drug!

Intuitively, it makes sense. Life and growth are inextricably linked, as are death and destruction. Unrestricted cellular growth leads to cancer/tumors, unrestricted cellular destruction also leads to cancer, but of autoimmune origin.

In other words, it's just the kind of effect natural selection is renowned for: odd, hackish solutions that work to solve proximate problems

Funny, this is industry-accepted programming practice too. I'm going to call it "evolutionary programming" from now on :D.

Arm the teachers?

> I first wondered if OP means that first answer with the obscure and horrible programming analogy

It's also factually wrong.

> Ever heard of the concept of interrupts? Basically these are functions that are executed immediately, whenever a specific condition occurs. These are one of the better ways of responding to a stimulus.

> Now, our body (the female's body) does not have interrupts.

> So what it does it set a while loop and in each while loop it checks for the presence of a fertilized egg.

We do have "interrupts". The brain floods the blood vessels with all kinds of hormones for an immediate call to action all the time. It's called the fear response. We'd be completely screwed if we had to rely on a "while loop" for that: getting run over while crossing the street would be the norm, because we'd lack the impulse to draw our attention away from our thoughts.

In theory, females could spontaneously ovulate when they have sex. Heck, in theory the brain could have evolved to decide whether or not it wants to. Nothing in Suzanne Sadedin's explanation gets in the way of this either. That would be an interesting shift in power balance - it's like the pill, but without hormonal hacks or dependency on external support.

This may be the best example of mansplaining I have ever seen: a tech guy posts a completely unsourced hypothesis as fact, but if you're a nerd with déformation professionnelle, it has a compelling narrative[0]. A woman who is an expert in the matter (PhD in evolutionary biology!) posts a long explanation with sources, the topic is female physiology. Yet which answer is shown first?

[0] https://en.wikipedia.org/wiki/D%C3%A9formation_professionnel...

Please don't use uppercase for emphasis. This is in the site guidelines: https://news.ycombinator.com/newsguidelines.html.

Thank you, I was not aware. Corrected.

> mansplaining

Don't be sexist. Maybe it's because his answer is shorter and hers exceedlingly long? Or is it because people like analogies (even wrong ones) more than scientific references?

What you are talking about is that people decided his answer is the best one. Which is the part where society encourages mansplaining. Note that this is Quora, supposedly a place where people have higher education and understand the importance of references and fact-checking.

There is an important distinction between structural sexism and individual sexism. And doing something that is sexist, racist, homophobic, you name it, is not necessarily tied to intent nor to consciously believing women/ethnic minorities/LGBTQ people are worth less than straight cis-male white guys.

Mansplaining is when a man does not realise that they don't know what they are talking about and just posit their own narrative as fact. It is a result of society's gender norms training them to do so. For men to be considered "real men", telling a compelling story with confidence is more important than bing correct - the scientifically appropriate level of self-doubt and "well this is what we know, here are my sources" is not "manly".

This is Toxic Masculinity in a nutshell: societal norms for what it means to be a "real man" that are detrimental to society and all genders - there are plenty of things that guys should do to prove they are "real men" that are detrimental to them too.

His answer and the societal norms that lead him to that thought process to post that answer, are an example of a toxic norm that most people aren't even consciously aware of. The sooner we acknowledge that and fix this, the sooner we are all liberated from structural sexism and toxic masculinity (and I do mean all - I feel very inhibited by toxic masculinity as a guy, and I think all men are).

Arush's answer is an example of mansplaining. The fact that it is about menstruation makes it even more ironic. That does not make him an asshole, nor someone who believes women are inferior to men - he acknowledges Saredin's answer as excellent. It just makes him unaware of all the structurally sexist norms that he subconsciously is bound to. And the same applies to the people who voted for his answers unaware.

> For men to be considered "real men", telling a compelling story with confidence is more important than bing correct - the scientifically appropriate level of self-doubt and "well this is what we know, here are my sources" is not "manly".

Well, I guess I'm not a real man then. Thanks for your mansplanation!

Before continuing the conversation, can I ask you to take a moment to step back and ask yourself with honesty whether you think that these statements imply that I am saying that you are not a good person because you also behave this way.

Because if so, there is a - perfectly reasonable - misunderstanding of my intent here. Read what I wrote again, more closely: all it is describing is a societal norm that I would like to get rid of. If you think you don't act that way, great!

This is not an accusation, it would be a perfectly understandable response (I get defensive all the time when my GF points things out to me).

At no point am I talking about you, nor saying that you are "not a real man". At no point am I saying that you are a bad person if you do or do not act this way. I'm sorry that you feel defensive, but there really is no need to. I'm not accusing you, nor would I blame you or any man for having toxic masculine behaviours. It's not your fault to be raised in a society with those norms, after all.

If you have the time, please watch Why Are You So Angry? by Innuendo Studios[0]. It also goes into how societal norms about good and evil train us to think things are about us and personal attacks when they aren't (the video highlights gamergate, but the process is not gender specific).

But the short version is: people tend to get very defensive about topics like sustainability, feminism, racism, animal rights, etcetera, because it makes them question whether they are good people or not. But ultimately, that is a self-centered response. Whether or not one's actions make them a good person is ultimately less important than whether or not what they do is the right thing to do.

[0] https://www.youtube.com/watch?v=6y8XgGhXkTQ&list=PLJA_jUddXv...

Right thing as decided by whom? E. g. I think that to eat meat is a right thing for himans to do. Not imagining things and forcing your imagined world on others is also the right thing to do.

Ironically, the right thing as decided by the meat eaters who feel uncomfortable around vegetarians. Watch the video to see the explanation, but the whole point is that vegetarians who don't enforce their views on others still have to deal with people getting defensive around them.

I had a similar experience when I refused to drink alcohol as a student: I don't mind others enjoying it, I just happen to not like it. Yet a lot of my friends in college felt like I was judging them.

people decided his answer is the best one.

Click on "View Upvoters" in each answer. His has 98. Hers has 21432.

I don't know WTF is Quora basing their raking on; apparently it's an algorithm that combines a bunch of factors: https://www.quora.com/How-does-the-ranking-of-answers-on-Quo...

Please don't brings facts into an ideological discussion! /s

I was just making a small factual note; I don't think it changes vanderZwan's overall point vis-a-vis the answer itself.

Thank you, I was not aware of this.

What if the same answer was posted by woman?

It wasn't.

Or maybe the other one was posted first and collected a lot of upvotes despite being factually wrong. I responded to a question once simply because the one being upvoted was so factually inconsistent and impossible. My answer has been upvoted a lot, but not as much as the other due to it being live longer.

So a part of me is literally attached to my mum's brain?

The wallet-controlling part I'm guessing.

Please don't do this here.

Perhaps, linking this post to this link would be better: https://www.quora.com/Why-do-women-have-periods-What-is-the-...

perhaps the most gripping read of any hacker news post ever. seriously entertaining and informative!

Seriously! This was unbelievably compelling!

I wish I had teachers like this. I found most of history, most of my primary and high school (i.e. several different teachers) excrutiatingly boring. Then I read a book on the economic history of the world that didn't just present raw facts, but also why things happened (i.e. stories) and it was one of the most interesting things I've ever read!

Which book on economic history was that?

I've no idea. It was short, probably less than 50 pages, covered the period since about 1500. A friend sent me a .pdf but I can't find that email, or the pdf, I've tried searching before.

Yes, I know that feeling. I had This is Water essay by David Foster Wallace in an email and I couldn't find it and the page I had bookmarked was gone too. I was so upset. The essay keeps coming back in my thoughts.

Agreed. This one and the earlier article "War in the womb" posted in 2014 (https://news.ycombinator.com/item?id=8155153) fundamentally changed my understanding of pregnancies.

Mice and rats are an interesting case, since they have hemochorial placentae but not menstruation. This somewhat undercuts TFA's "this because of that" narrative. (Really the only flaw in a wonderful article.) Evolution is weird.

Apparently some mice do menstruate[1]. Do mice have another mechanism for handling the issue the author raises: "What to do when the embryo died or was stuck half-alive in the uterus?"

[1]: https://www.nature.com/news/first-rodent-found-with-a-human-...

I would speculate that it works similarly to most other mammals. Spikes of prostaglandin in the blood cause abortion via smooth muscle action and fluid production (or, if the embryo has developed to term, parturition rather than abortion). Prostaglandin is produced in the body cyclically. The corpus luteum releases progesterone that counteracts prostaglandin, but toward the end of the estrous cycle the CL degrades into an inert corpus albicans. Healthy implanted embryos release gonadotropin, which "stops the clock" for the CL so that it continues to produce progesterone. Eventually the placenta starts producing its own progesterone, and at that point the CL is no longer important. A dead or half-alive embryo is likely to produce neither gonadotropin nor progesterone, so it will be aborted and flushed on the next prostaglandin spike. The later this occurs in the pregnancy, the more stress is placed on the mother.

It's my impression that after implantation, this process is the same in humans as in other placental mammals. Thus menstruation might be more properly understood to be about flushing unimplanted zygotes rather than aborting unhealthy embryos.

> This somewhat undercuts TFA's "this because of that" narrative. (Really the only flaw in a wonderful article.)

You're underselling this flaw, because it's fatal. A major issue with a lot of pop science is this exactly: the author is much too confident in connecting disparate ideas (because it serves good storytelling and increases trust in the author), when in actuality it's very dangerous to assign intent to things like evolution. For example, a common statement you hear is "evolution caused..." Evolution doesn't have a will or do anything deliberately, nor does it always tend towards the best way to do something or a beneficial mutation. The author also engaged in this flaw by giving fetuses wills (similar to how some writers anthropomorphize animals including primates). So while the doctor goes on in the whole post comparing different species and their different gestational evolution, at the end of the day, it's just a theory that combines different points.

Edit: Downboats? Berry?! Not on my HN!

> The quotes are to indicate that this isn't about what they consciously want, but about what evolution tends to optimize.

Sounds like the author tries to address your point.

Even Wikipedia describes placentation like a siege:

> The trophoblast, which is a collection of cells that invades the maternal endometrium to gain access to nutrition for the fetus, proliferates rapidly and forms a network of branching processes which cover the entire embryo and invade and destroy the maternal tissues. With this physiologic destructive process, the maternal blood vessels of the endometrium are opened, with the result that the spaces in the trophoblastic network are filled with maternal blood; these spaces communicate freely with one another and become greatly distended and form the intervillous space from which the fetus gains nutrition.

>"Researchers, bless their curious little hearts, have tried to implant embryos all over the bodies of mice. The single most difficult place for them to grow was – the endometrium."


It's the thunderdome, but not as bad as a shark uterus. They generally only give live birth to one shark because that shark has eaten all the others.

And sharks including threshers, makos and great whites have an even odder solution: They feed their fetuses an endless stream of unfertilized eggs.

2. Sibling cannibalism

Sand tiger sharks have the most ghoulish fix for hungry babies: The fetuses devour each other in-utero until there’s just one pup remaining in each of their twin wombs. This uterine bloodbath is thought to have developed because a litter of sand tiger pups usually has multiple fathers — and each dad is engaged in a proxy war for his genes to take the upper hand. The “winning” fetus gets all the nutrients from its siblings and a roomy womb to develop into an unusually big baby, over 1 meter (3 feet) long at birth. Being born large and well-developed helps these newborn predators survive in a hostile ocean.

My first thought was right on top, in various layers: skin, fat, muscle, etc.

Nope. They did the brain, testis, spleen, liver, and kidneys.

> Normal mammalian pregnancy is a well-ordered affair because the mother is a despot. Her offspring live or die at her will; she controls their nutrient supply, and she can expel or reabsorb them any time. Human pregnancy, on the other hand, is run by committee – and not just any committee, but one whose members often have very different, competing interests and share only partial information.

Such eye-opening and fascinating analogy.

Thanks for the quote. That said, please don't use indentation to set off block quotes, as it makes it very difficult to read, especially on mobile devices.

Common methods of block quoting on HN is prefixing with ">" and possibly using asterisks to italicize the text, and possibly wrapping it in quotation marks.

Thanks for the tip, I checked it up on mobile, it's indeed hard to read. Should be better now.

Fascinating. Reminded me of the The Selfish Gene, especially the part discussing the opposing objectives of the mother and offspring.

The Selfish Gene isn't wrong, but its not true either. It's true your genes exist in you, and they generally evolve to survive.

However, "Selfish" genes can do some rather unequivocally selfless things. E.g. symbiosis.

Symbiosis isn't exactly selfless; it benefits both organisms involved.

Even if you mean altruism though, a gene for altruistic behavior can still be selfish. For example, if Gene X causes an organism to sacrifice something for another organism that carries also carries Gene X, the gene will be promoting its own survival.

It's not exactly selfish either. You realize there is a benefit to cooperation. Most cell organelles are product of symbiosis.

lukas099 is arguing one of the central points of the book, that altruistic behavior is inherently selfish on a genetic level.

You seem to be arguing completely based on the title of the book, which itself makes clear that the title is provocative but not entirely accurate, which makes me think you have not read it.

I am aware of that, and I'm arguing, that is a very reductive model of how humans behave.

E.g. when given choice, humans tend to help each other much more than a selfish gene model would behave, i.e. help people and strangers you have no connection with.

But all of that is discussed at length in the book we're talking about. To pick out the word "selfish" and say that that's the gene model displays to me that you haven't read the book.

It's difficult to defend a book's premise from someone who hasn't read it and just wants to debate the meaning of the title.

Look, I'll be honest. I didn't read a book.

But I don't want to debate its title, instead its reductionist view of people nothing more as vehicles for the immortal DNA.

Anyway here is the part that I was referencing:

    The self-selecting process predicted by the selfish-gene model 
    becomes quickly skewed when correlations in reproduction
     exist which give rise to less than complete mixing of alleles 
    in the gene pool. This may occur through several mechanisms,
     including mate selection and partial geographic isolation.

    The gene-centered view, Dr. Bar-Yam points out, can be  
    applied directly only to populations in which sexual  
    reproduction causes complete allelic mixing. (Such 
    populations are called "panmictic" in biology.)

    Many organisms are part of populations that do not 
    satisfy this condition. Thus, the gene-centered view and 
    the concept of the "selfish gene" does not describe the 
    dynamics of evolution, Dr. Bar-Yam concludes.
Source: http://www.necsi.edu/projects/evolecol/selfishgene.html

>Look, I'll be honest. I didn't read a book.

>But I don't want to debate its title, instead its reductionist view of people nothing more as vehicles for the immortal DNA.

The problem is that the book does not expound this reductionist view; it is only your conception of the book (likely based on the title) that does.

Except it absolutely does:

    We are survival machines – robot vehicles blindly
    programmed to preserve the selfish molecules known as genes.
    This is a truth which still fills me with astonishment.
Richard Dawkins, The Selfish Gene.

As lukas099 has said, the book does not take the view that you're saying it takes.

Cherry picking quotes out of the context of an entire book can get you to any conclusion you want to come to, especially if you don't know the rest of the contents of the book.

I encourage you to read the book before taking a side that you read an article about.

You still are dodging addressing my points, before going into a "READ THE BOOK" mode. I don't have to read the Bible to realize how it was made and why is it flawed... Similarly, I don't need to read the book, to know the inclusive selection theory on which The Selfish Gene was based is flawed, and hasn't lived up to its models.

EDIT: Started reading it:

    The replicators that survived were the ones  that built survival  machines  for themselves   to  live in...
    We  are  all survival  machines  for the  same kind of replicator—molecules called DNA—but there  are many...
My former quote sure is misinterpreting things /s

Yes. Amazing book. The Red Queen as well.

If I read anything about human reproduction, I remember "The Egg and the Sperm: How science has constructed a romance based on stereotypical male-female roles" by Emily Martin. https://web.stanford.edu/~eckert/PDF/Martin1991.pdf one quote in relationship to the comparison between ovulation and spermatogenesis: "By extolling the female cycle as a productive enterprise, menstruation must necessarily be viewed as a failure."

While the post was very entertaining, it did not actually answer the question. We don't know why higher primates (and bats) have periods.

> The solution, for higher primates, was to slough off the whole superficial endometrium

Doesn't that suggest that's reason for higher primates? Or are you disagreeing with the author of that post?

This is the hypothesis, but no evidence to support this theory is advanced. We don't know that higher primates (and bats) have more aggressive embryogenesis than other animals that don't have periods.

Did anyone get a pop up on the page saying the page was "reestablishing internet connection, click here". I clicked but immediately felt pretty stupid, I never just click on things but this was so... normal. And why would a page and not the browser report this?

Same story illustrated by TED-Ed, which I would suggest you to watch: https://youtu.be/cjbgZwgdY7Q I happen to watch it few weeks ago and this reminded me of it.

What a brilliant piece of writing! Very compelling.

Ummm.. someone I know did not have the menstrual cycle (had for only 2 initial years) but she still has 2 kids healthy and fit.

After reading this, I just miss my mother so much. Can't imagine what I've done since I'm still a fetus.

Shorter version: menstruation probably only exists to potentially flush failed pregnancies.

TL;DR => Menstruation in human females is a monthly self-cleansing (although wasteful) FLUSH to get rid of all those "unworthy" scum who didn't make it as viable fetuses. Because being considered "worthy" by mother grants you (the fetus) root-level, administrator access to her body (Yes, we human fetuses are that aggressive and we don't know why!). So be warned that there is a tough screening process going on before you get accepted and gain root-level permanent access!!! Otherwise you will end up in nasty menstrual blood!

It actually supports pretty much all of Dr. Sadedin's details if you read past the first half of the BBC article, which describes previous discredited theories.

That article was better than the OP, given it is less of a narrative and instead presents how research and theories have evolved over time.

Very interesting answer from Suzanne Sadedin. Very odd that "Arush Kakkar, Founder, CorsecoTech", who appears to neither be a physician, nor a medical science expert, nor a woman, is the highest displayed answer for me, with a strained analogy relating women's bodies to software, which is based on Suzanne's answer. I don't know if this is because of user voting, his score, or the Quora algorithm. I wonder if the mysteries of this ranking system are what lies behind the Quora login wall.

Sadedin's post has over 20k upvotes, but that guy has 81. Definitely not because of user voting.

It's fallen to #2 now. I would bet it's recency bias; that guy is probably there from this Hacker News link, made a follow-up answer, and because Quora (like HN and many forums) tends to put new replies at the top to give them a chance & see how they do with voting, it momentarily showed up as the top answer.

Quite the opposite; his answer was from Jan 2015; the good answer arrived nearly two years later.

I'm not terribly familiar with Quora's UI, but it looked like that's the date that the person's author profile was last updated, not the date that they answered the question. I could be totally wrong on this though. It's not possible for the good answer to have arrived later, because the bad answer references it (unless he edited the post afterwards to refer to it, but if the date on the post is actually a last-edit date for the post, that still wouldn't make sense).

Oh, I think you’re right.

His answer is kinda crap, to boot. Menopause isn't triggered by the number of menstrual cycles, but by age.

How do you know that? It is and a cop out answer because age is not a mechanism. Specifics please?

I apologize. It turns out my intuition was wrong about this. I just assumed that menopause was triggered by age, and I was going to look for evidence that age of menopause doesn't correlate with number of pregnancies, but it turns out it does! Childless women hit menopause earlier, on average. So, I guess I don't know.

Isn't it sexist to think that women would know more about the scientific reasons they menstruate than men? At least that's what your answer is implying...

Artificial wombs can't happen soon enough, it's the final challenge to equal rights.

Strictly speaking, they can. The period occurs at the end of a cycle, so it's possible to get pregnant on your very first cycle without ever having had a period.

The likelihood of this happening is extremely low of course.

Strictly speaking, the question is asking why women can't get pregnant without the menstrual cycle. As you mention in your post, the period occurs at the end of the cycle, therefore without a cycle, pregnancy will not happen.

No. Menstruation occurs if there's no implanted and viable fetus by ~24 days after ovulation. A few days later, ovulation occurs, and the cycle repeats.

What are you saying no to?

Maybe I read it wrong. Pregnancy and menstruation are alternate endings for the cycle. So, as GP said, a woman could theoretically get pregnant on her first cycle, without menstruating.

I think you are agreeing with the comment you responded to.

Maybe so. Too late to delete.

Can you provide a car or software development analogy?

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