Superfetation: When You Get Pregnant… Even Though You’re Already Pregnant

Superfetation: When You Get Pregnant… Even Though You’re Already Pregnant


[♪ INTRO] There’s so much about the human body that we think we understand, but then weird stuff happens that changes everything. Take babymaking, for example. Two fertile people have sex, their egg and
sperm meet, and then about nine months later, a new human enters the world. Or so the story goes. Well, hold on to your ovaries, folks. Because rarely, after someone gets pregnant, they can get pregnant again. And no, I don’t mean shortly after having
a baby. I’m talking about getting pregnant days
or even weeks after conceiving, and carrying both fetuses at the same time—what scientists call superfetation. In humans, superfetation is super rare, but
also super real. And scientists have been studying these strange
cases of twinning for insights into how reproduction
works. Normally, a person releases one egg per month from their ovaries. If sperm fertilizes that egg within about
a 24 hour period, its cells begin to divide. As that happens, part of the ovary produces
hormones like progesterone which help prepare the uterus
for implantation. And then, if those hormones do their job,
about six days later, the quickly-growing clump of cells burrows
into the thick layer of tissue lining the uterus and implants. After that, the body continues to suppress
ovulation, and the lining of the uterus changes to accommodate
the growing fetus— changes which also make it less receptive
to implantation. But the uterus isn’t completely unreceptive
for several weeks. Finally, about a month after implantation, the opening at the bottom of the uterus called
the cervix forms a mucus plug. This protects the fetus from pathogens and
prevents sperm from coming in and fertilizing another
egg. Now, obviously, twins and other multiples
are a thing, so we know that more than one embryo can implant. But that’s typically because an embryo happens
to split itself into multiple identical copies at an early
stage, or because the person released multiple eggs
to begin with. That means multiples generally occur before the suppression of ovulation, the decrease
in uterine receptivity, and the formation of the mucus plug. For superfetation to occur, allllll of these
barriers have to be circumvented or go awry. Which obviously doesn’t happen often. But it does happen. Like, in a case from the late ‘90s. A women had a set of twins that consistently
measured four weeks apart based on ultrasounds, which use the length of a fetus’s spine to determine its gestational age. Doctors working on the case ruled out other
reasons for this difference in size, like genetic
conditions that could restrict growth. And other than there being two fetuses of different ages in her womb, the pregnancy was unremarkable. The person delivered both vaginally when the oldest was forty weeks of age. We don’t know exactly what happened in this
case, but her doctors suggested atypical levels
of hormones that could have encouraged her to ovulate
after implantation. Then, so long as some sperm managed to make
it past the cervix before the mucus plug locked
them out, the second embryo could have settled into the uterine lining before receptivity was
totally gone. Or, the woman may have released more than
one egg during ovulation, both of which were successfully
fertilized. In that case, the only reason she didn’t
have normal twins was that the second experienced delayed implantation. Basically, the doctors thought it may have
pressed pause on its development and hung around in the
uterus for a few weeks before implanting, getting
in just under the wire in terms of uterine receptivity. Other known cases of superfetation have involved people with uterus didelphys: a rare condition where a person has two uteruses… and therefore, can become doubly pregnant. One such case gave birth to two healthy babies whose ages were more than a month apart! From what doctors can tell, it seems like
the two uteri can function independently—so implantation
in one doesn’t prevent implantation in the other. And sometimes, these uteri even connect to
different vaginas, so there’s no mucus plug blocking sperm from reaching the egg if the person ovulates! Scientists also hypothesize that the use of
assisted reproductive technologies can make superfetation
more likely. Still really rare, but, you know, a little
less so. And this probably has something to do with hormones taken during the process. With in-vitro fertilization, the egg donor
often receives hormones to induce more than one egg to mature at the
same time. The mature eggs are then retrieved with a
needle and fertilized with sperm in a lab. Once fertilized, two or three of these embryos are transferred into the uterus, often while
the person receives supplemental progesterone. That’s the hormone we mentioned earlier that helps prep the uterine lining for implantation. It also maintains that lining during pregnancy, so people undergoing IVF often stay on it for awhile after conception. The thing is, that progesterone might keep
the uterus receptive to new implantations longer. And that seems to be exactly what happened in a 2005 case where one triplet was estimated
to be eight weeks younger than its two siblings. In fact, the doctors involved in that case
suggested growth discrepancies between multiples could
be due to superfetation more often than we think. Even though known cases of superfetation are
vanishingly rare, it’s possible that some have gone undetected— especially in relatively older people carrying
fraternal twins. That’s because as people with ovaries age, there’s a slightly increased chance of what’s
called a luteal out-of-phase event, or LOOP event: an abnormal surge in hormones 1 to 3 weeks
after conceiving. These hormones could spur an additional ovulation, and even make the cervical mucus plug porous
enough for sperm to get through and fertilize the
egg, just in the nick of time to implant. And, well, it’s not uncommon for fraternal
twins to be different sizes, so scientists are trying
to suss out whether some seemingly-normal twins are actually cases of superfetation. In any case, there’s no need to worry about abstaining from sex while pregnant if your
doctor has given you the go-ahead. This phenomenon is super unlikely to happen. Still, researchers are continuing to study
these rare cases to help us better understand how the human
body normally conceives and progresses through
pregnancy, and how it can sometimes throw a curveball
instead. Thanks for watching this episode of SciShow! And a special shout out to our channel members. Those are the people in the comments and chats with the cool badges and using special emojis — like Hank’s head. Their support helps us keep making fun, educational videos like this one, so we really appreciate it. You can learn more about becoming a channel
member by clicking the “join” button below. And, if you’re not sure what to watch next… well, we have a whole episode about what usually happens during pregnancy. So maybe start there! And let us know the weirdest thing you learn
in the comments. [♪ OUTRO]

100 thoughts on “Superfetation: When You Get Pregnant… Even Though You’re Already Pregnant

  1. For the love of God. A person can't get pregnant. ONLY a woman can and only a mans sperm can fertilize it. Stop calling them a person. I like this channel but calling an obviously a woman a person or man a person is obnoxious. Even halfway you start call them a woman. Just please stick to what it is.

  2. This all sounds absolutely horrible.

    Of course, I'm of the opinion that all of the permanent changes that happens to a person during pregnancy just means that reproduction is a series of horrible events that (hopefully) ends with a desirable outcome.

    I have no idea why so many people I know actually classified such a thing as a life goal. And the superfetation prospect? Even worse.

  3. Now I have a fear of getting pregnant, imagine the shock of being announced your pregnant again at 6 or 7 months…

    I'm a man

  4. My mom had "suffered" from this with me and my brother. He got born 5,5 years after me. I guess he forgot to unpause (3:24) and took him a while to … u know … get out. Fking camper …

  5. The most shocking thing to me from this video is that there have been women with two separate and independently functional reproductive systems.

  6. My brother and I were suspected to be this type of twin because I was so small but it was the early 80s and we were emergency c sectioned so they couldn’t tell for sure.

  7. People with ovaries… women. That is the word to describe us and it’s nothing to be ashamed of! Especially for a scientific channel.

  8. well did this happen to my grandma? Because my uncle and my mom are the same age for one month. like when my uncle turns 43 my mom is already 43 but when the next month comes my mom turns 44.

  9. I read in an article about a woman in India who gave birth to a baby and three months later she went into labor again and had another baby. She had two uteri. Which she did not find out, since she was poor and did not get an ultrasound.

  10. Still have to zoom in every time I see her to be sure that that's not snot hanging out of her nose.
    Edit: Particularly, when she sounds so nasally and congested. Not the best combination if you're going to have something mucus colored hanging out of your nose.

  11. Superfetation is yes extremely rare in humans……….but it happens with much more frequency in domestic cats. Still not common but it's a well known thing among vets.

  12. Just say "woman" 🙄 otherwise it's only catering to the malignant narcissism of a negligible percentage of the population that cries foul.

  13. '..people with ovaries..'
    '.. the person delivered both [children] vaginally..'
    et.c.
    It's WOMEN, the correct term is WOMEN!
    A pregnant person would also be a pregnant WOMAN.
    (0:25 '.. someone gets pregnant..' NO. Only women do that. WOMEN get pregnant.)

    Yeez, this political correctness is devastating. So, just because people identify as this and that, now women must forego their claim to the term WOMAN?!????
    I expected more adherence to science from SciShow. This is preposterous.

  14. 'normally a person releases one egg per month from their ovaries'
    when a science show is too scared of public backlash to use the words WOMAN and HER, you know the future is bleak

  15. Husband: "wanna have sex?"
    Pregnant wife: "why not, I couldn't get more pregnant."
    Mother nature: "bwaa haaa haa haaa, that's what you think."

  16. I get why you use person instead of woman/man when you speak to the general audience because some identify as a different /non gender person and thus you include them when you say a person with ovaries. But in the case of the person around 3:30 shouldn't you call her a woman if she identifies as one? Calling her a person instead of a woman indicates that she also not identifies as a woman. Which could be possible but unlikely.

  17. Imagine the horror of finding out you got this chick here pregnant? Permanent Mexico road trip! Adam….? Mi nombre es Eduardo Sanchez.

  18. Person? Pregnant can be only WOMAN… Idiots. Stop indoctrinate people. Or maybe, just maybe.. you get some extra money for this?

  19. Fun fact: Greek mythology has A LOT of case like this, A LOT… and obviously Zeus (and Apollo, in the case of Gemini) was behind all this.

  20. I once got my wife pregnant off a single shot.
    We live in fear of her getting pregnant via a broken condom or something.
    Easy to forget how much others suffer trying to conceive.
    Don't judge us for not wanting kids; we already have 2 and I want another but we don't have the time, money or love to give to a third without the first two getting less.

  21. I knew someone that this happened to but the two children were from different fathers. She said she slept with the men less than 24 hours apart.

  22. Thank you thank you for always using gender neutral language for people who have uteruses and pregnancies. I feel so validated and included!

  23. Alternatively, you could have something probably similarly rare (or actually, probably even rarer) as with what happened to give rise to my ex. That is to say, a woman being a surrogate mother, but also getting pregnant with her own kid at the same time, and then one embryo absorbed the other to give rise to a chimera with four parents. One with two sets of functioning reproductive organs, of different genetic heritages. One who, in theory, could maybe potentially impregnate herself. Probably one-of-a-kind, no?

    (I've checked, you won't find a case study of her online, at least if you're searching through the methods of a normal, non-medical professional, even knowing her and her parents' names, her age, and the hospital she was born in. She's from Texas. Go nuts)

  24. So someone at some point had a baby and then one month later had another baby, what? I wouldn't want to be in those shoes especially considering that during the one month delay, she has to care for number 1, who I hope for her was one of those babies which did it's nights alright (probably not). oooohhh the anticipation during that time span must be amazing, just to go through the whole ordeal again so you can end up with double trouble. Nice!

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