Sometimes the LawOfInverseFertility hits so hard that the woman doesn't even realize she's pregnant, often not until the ScreamingBirth (and sometimes not even then). Cries of "ButICantBePregnant" and "how could I have missed this?" ensue. For whatever reason, when they ''do'' notice before giving birth, it isn't the lack of [[NoPeriodsPeriod periods that tips them off]], but rather the morning sickness and WackyCravings. It seems that heroines just don't keep track of their monthlies. Cue BabiesMakeEverythingBetter!

This is TruthInTelevision, in several ways.

* When they near menopause, women's periods can become erratic, making them more difficult to track. Couple this with the fact that menopause takes time and doesn't occur at the same age for every woman, and older women can have an unplanned child whose college years will coincide with their own retirement.
** Similarly some younger women can have health issues that make fertility unlikely or erratic.
* In many eras, sex education was non-existent or pathetic, and some young women simply ''didn't know'' the details surrounding pregnancy and its cause.
* Even for young, healthy, well-educated women, pregnancy can end up a surprise. Sometimes implantation of the embryo can cause minor bleeding and the woman can mistake that for her regular period. Read the [[note]]Roughly once a month, a woman's body builds a lining on the uterus to defend against the possibility of pregnancy. Human pregnancies are more invasive than most, a trait shared with other primates, some bats, and the elephant shrew. The shedding of this lining is menstruation (you may have noticed dogs and cats don't menstruate; in fact they and other placental mammals reabsorb the lining. So do human women, just not all of it). The embryo implants in this lining by using enzymes to dissolve a portion of it just a little bit. This can cause some spotting that, except for the amount of material, would be identical to menstruation.[[/note]] for more details. Or possibly the woman, like most women, leads a busy life and doesn't necessarily keep close track of her periods, relying on [[HystericalWoman the warning signs]] to keep from making a mess.

Not to be confused with ButWeUsedACondom, but it's likely to be a result.

'''Beware, all spoilers are unmarked.'''
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!!Examples:

[[foldercontrol]]

[[folder: Anime and Manga ]]

* ''GreatTeacherOnizuka'' -- Kunio Murai's AbsurdlyYouthfulMother didn't realize the implications of her sudden weight gain at first.
* In ''Manga/KodomoNoOmocha'' Sana's biological AbsurdlyYouthfulMother mom Keiko actually didn't know she was preggers ''until she gave birth''. Somewhat more understandable in the manga, where Sana's birth happened when Keiko was 14 (she's still very young in the anime, but not THAT much), and it's strongly implied she's also a ChildByRape.
* This happens to Shigeru in ''AkkanBaby'', though in her case it's not so much "ButICantBePregnant" as "how is babby formed?"
* This trope was played tragically straight in ''{{Berserk}}'', where Guts and a now insane Casca only discovered that she was in her beginning stages of pregnancy after she miscarried their child under the severe trauma that she sustained from the Eclipse [[note]]A few fans believe that Casca might have known she was pregnant before she went insane and either never got the chance to tell Guts or [[MySecretPregnancy didn't want to tell him]] out of consideration that he would stay with the Hawks out of duty instead of pursuing his dream[[/note]].

[[/folder]]

[[folder: Fan Fic ]]

* Used as a "plot twist" in ''way'' too many fanfic. It gets one conditioned to expect it any time someone is eating more than usual, [[MorningSickness puking]], gaining weight, or [[WackyCravings craving odd foods]] in any medium, including real life.
** Though it is justified in the occasional fic where MisterSeahorse comes into play.
* This trope shows up in the {{NGE}} FanFic Fanfic/TheSecondTry. However, the "surprise" in this case is rather warped due to couple in question being ''[[DysfunctionJunction Asuka and Shinji]]''. Due to her mess of insecurities, Asuka was rather freaked out when she discovered she was pregnant and had tried to hide it from Shinji (She even went as far as to ''starve herself'' in a misguided attempt to induce a miscarriage). He only found out after a rat got into their trash and he stumbled onto a positive pregnancy test Asuka tried to hide. To say he was surprised would have been an understatement.
** Incidentally, Asuka avoids the usual markings of trope, as what tipped her off to her condition was missing one of her periods.
* In the backstory of Kyon's mother in ''Fanfic/KyonBigDamnHero'', it took a while for her to realize she was pregnant of Kyon due to a mix of ignorance and her lack of physical growth, compounded by a FriendlessBackground and a strained relationship with her parents.
* In the SailorMoon story "Misconception", the plot is kicked off when Usagi learns about Chibi-Usa's previously-unmentioned older brother. One whose birthday is roughly eight and a half months away...
** As with the above mentioned Second Try case, It was only Chibi-Usa's comment that revealed it to Usagi. The ensuing nausea was from the shock and stress of learning she was going to be a mother far earlier than she realized, not morning sickness.
[[/folder]]

[[folder: Film ]]

* The Creator/MontyPython movie ''Film/MontyPythonsTheMeaningOfLife'', previous to the infamous "Every Sperm Is Sacred" song, featured a poor Yorkshire family whose mother was having babies drop right out from between her legs as she cooked and cleaned for her burgeoning family. This may also be implying that it's less that she didn't know and more that she didn't care, since they had dozens of children already.
* The new cute swimming instructor in ''WaterBoys'' discovers she's eight months pregnant and goes on a maternity leave immediately after managing to convince her five team members to throw away their pride and join her synchro-swimming team for her.
* Emmeline in ''TheBlueLagoon'' becomes pregnant with Richard's child and has no clue whatsoever until ''after'' she's given birth. She even tells Richard she doesn't ''know'' why she had a baby. Justified due to them having been living on the island since they were children and having no formal sex education whatsoever.

[[/folder]]

[[folder: Literature ]]

* In the satirical 'legend' of Pope Joan, a woman went to Catholic school disguised as a boy and worked her way through the ecclesiastic ranks to Cardinal and finally Pope. Her cover was blown when she put her foot in the stirrup to mount her horse and promptly gave birth before a shocked audience.
* In a subversion, Maya Angelou relates that she knew she was pregnant in ''IKnowWhyTheCagedBirdSings'', but the surprise was certainly on her family after she hid it from them for eight months.
* Implied in ''Discworld/TheFifthElephant''. Even if Lady Sybil wasn't surprised, [[CrowningMomentOfFunny her husband most assuredly was]], and his stupid questions and her dry responses are particularly [[HilarityEnsues hilarious.]]
* Daisy's mother in ''TheStoneDiaries'' is unaware that she's pregnant.
* Bluestar in ''[[Literature/WarriorCats Bluestar's Prophecy]]'', thanks to her one-night stand with Oakheart. She is unaware of her pregnancy until another cat points it out.
* A double-subversion from Literature/TheBible: Sarah has overheard three men (actually [[AngelUnaware angels in disguise]]) telling her husband that he and Sarah will have a son. She laughs because [[ButICantBePregnant she is old and has been infertile for a long time]], and gets [[WhatTheHellHero called out]] for laughing by the angels, which shuts her up. Sure enough, she does become pregnant, and she names her son Isaac (because she laughed at the prospect of having a child at her age, and boy was she wrong!)

[[/folder]]

[[folder: Live Action TV ]]

* This happened to Peggy Olsen in ''MadMen'', such that she didn't know until she ''went into labor''.
* Was a plot point on ''{{Eastenders}}'' a while back where a teenager gave birth not having a clue.
* Happened to an obese woman in a first-season episode of ''StElsewhere.''
* The aptly-titled ''I Didn't Know I Was Pregnant'' is about this. See the "Real Life" category for details.
* A fat woman complaining of severe cramps went into the ''{{ER}}'' and not only realized that she was pregnant but that she was giving birth to twins. Dr. Benton had to deliver the baby--something he "hadn't done since med school."
** Elizabeth Corday gets hit with this in the seventh season. Her response to the news was a flat "That's impossible."
* ''Series/DoctorWho'' Series 6 gives one to Amy Pond. The surprise element is made more plausible, so to speak, by having the Amy we see be a (non-pregnant) duplicate with her consciousness, while her comatose (pregnant) real body is elsewhere.
* Happened in the latest series of "Series/{{Whitechapel}}" when DS Miles' wife fears she might have ovarian cancer only for it to turn out she's 6 months pregnant
* At the end of "Baby on Board", ''ModernFamily'''s third-season finale, Gloria [[ConfessionCam tells us]] she had thought she was carsick but, no, she's really pregnant, as the camera shows her buying a pregnancy test kit
* Appears in the ChristmasEpisode of ''Series/CallTheMidwife''.
* A minor point in the fifth season of Castle. [[spoiler:Ryan and his wife are having trouble getting pregnant... because they're already pregnant.]]

[[/folder]]

[[folder: Real Life ]]

* TruthInTelevision: According to The Learning Channel series ''I Didn't Know I Was Pregnant'', women who tend to be a risk for surprise pregnancies often assume they were infertile, or [[ButWeUsedACondom think they used proper birth control]], or have such irregular periods that they didn't notice the pregnancy, or are so ignorant about the signs of pregnancy that she mistakes them for an illness. Some women still experience spotting during pregnancy (and thus think that they're still getting periods), while others don't even get a baby bump--not even nine months in--or have a larger body shape that makes small(er) fluctuations in weight and build hard to notice.
* On either the same show or something similar, there was a story about a larger woman who had been thought to be infertile and thus didn't notice any of the regular signs of pregnancy. When she went into labor, she had been suffering from a bad case of constipation and thought she was trying to pass a bowel movement. The description she gives of what follows crosses the line from Nightmare Fuel into [[UpToEleven Nightmare Nitro]].
* A teen magazine once had a real life story about an 18 year old girl who hadn't gotten her periods yet. She'd had a boyfriend and hadn't used protection while sleeping with him because she didn't know that ovulation happens before the actual period comes. One day, ages after she and the boyfriend had drifted apart, she got some pretty strong stomach pains on and off. Thinking it was her first period, she just stayed on the toilet and ended up birthing a baby boy into it. The baby was okay, but her mother had to take care of him for a few weeks before the girl snapped out of her denial and started taking care of him herself.
* A story in relatively recent (as of September 2012) news was of a woman who did not know she was pregnant until she gave birth...in Afghanistan. ''In the middle of a war zone''. '''After serving as a bombardier in battle.''' (So she qualifies for PregnantBadass, even if she hadn't been aware of it.) Justified because the normal signs of pregancy (lack of periods, stomach pains, vomiting) can be chalked up to the stress of battle.

[[/folder]]

[[folder: Theatre ]]

* In the stage play ''E/R'' (basis for the half-hour 1984 sitcom, not the hour-long 90's drama), a mother brings her teenage daughter into the hospital emergency room, complaining of "stomach cramps". The girl continues to deny she's pregnant even as she's giving birth.

[[/folder]]

[[folder: Western Animation ]]

* In ''FamilyGuy'', Peter looks up one of his old girlfriends, who's turned ugly and obese in the intervening years. [[BlackComedy Then a baby splatters out from between her legs]], much to their mutual surprise.

[[/folder]]

[[folder: Web Original ]]

* On ''TheGuild'', Clara was well aware that she was pregnant. Her husband, on the other hand, was quite shocked to find out.

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