Sometimes the Law of Inverse Fertility hits so hard that the woman doesn't even realize she's pregnant, often not until the Screaming Birth (and sometimes not even then). Cries of "But I Can't Be Pregnant!" and "how could I have missed this?" ensue. For whatever reason, when they do notice before giving birth, it isn't the lack of periods that tips them off, but rather the Morning Sickness and Wacky Cravings. It seems that heroines just don't keep track of their monthlies. Cue Babies Make Everything Better!
This is Truth in Television, in several ways.
- When they're 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. (For example, PCOS.)
- In many eras, sex education was (and in some places, still is) 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 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 the warning signs to keep from making a mess. And some women keep having periods right through the pregnancy, though this is rare.
- Some methods of birth control "turn off" periods for extended lengths of time, which can make it very easy to miss the fact that a woman is pregnant until she's well along the way. Some types of IUDs (intrauterine devices) are becoming notorious for this.
- Hormones do change through one's life. So what might have been a "safe" day at, say, 25 might actually become a fertile day at 35.
- Stress, illness, anticipation, travel, and a whole slew of other factors can throw off even the most regular woman, which can lead to unexpected conception. (This is why, if you are planning on using "Natural Family Planning" as your preferred method of birth control, you continuously monitor your temperature/symptoms/cervical mucus/hormone levels/etc., no matter how well you think you "know your/your partner's body." Because things can change at the drop of a hat; there are a lot of variables at work.)
- Sperm can live for up to a week inside a woman's reproductive tract. So she can have sex on what is, in theory, a perfectly safe day (but is close enough to a not-so-safe one) and end up conceiving while going about her mundane business.
Not to be confused with But We Used a Condom, but it's likely to be a result. Contrast with My Secret Pregnancy, where the mother knows, but keeps it a secret from the world at large. May be justified in the case of a Mystical Pregnancy or a Mister Seahorse situation. Related to One Night Stand Pregnancy.
Beware, all spoilers are unmarked.
- Great Teacher Onizuka: Kunio Murai's mother didn't realize the implications of her sudden weight gain at first.
- In Kodomo no Omocha Sana's biological 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 than Sana is also a Child by Rape and the result of sexual abuse by Keiko's uncle.
- This happens to Shigeru in Akkan Baby, though in her case it's not so much "But I Can't Be Pregnant!" 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 .
- Concrete: neither Concrete nor Maureen, the biologist who studies him, even suspect he's pregnant until his back cracks open and there's a smaller him inside, despite him getting symptoms similar to humans like morning sickness and being even moodier than he normally is. Justified because not only is Concrete's body alien, but the baby was a result of asexual reproduction (though said reproduction was triggered by human sexual thoughts), Concrete's body is still in many ways a mystery, and everyone thinks of Concrete as being male as he was once a man.
- Exaggerated in The Umbrella Academy, when 43 women who hadn't been pregnant to begin with suddenly all give birth all the same time with no warning, right in the middle of whatever it was they had been doing at the time.
- The Second Try: Due to her mess of insecurities, Asuka flipped out when she discovered she was pregnant and had tried to hide it from Shinji; she even stopped eating in a misguided attempt to induce a miscarriage. Shinji found out anyways; a rat got into their trash while he was taking it out and he found 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 Kyon: Big Damn Hero, 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 Friendless Background and a strained relationship with her parents.
- In the Sailor Moon 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.
- In the Star Trek (2009) fanfic Safe and Sound we find out early on that Uhura is pregnant with Spock's child. She and the senior officers find out when the computer scans her and informs everyone (the biggest reactions come from Kirk and Scotty, the former spitting his mouthful of water into McCoy's face and the latter falling off his chair). This one is justified in that she was only one month along (before she would have noticed the missed period and before morning sickness came into play) and she and Spock didn't take precautions because of a certain incident which happens to Vulcans every seven years.
- In the Star Trek (2009) fanfic Kirk Starts A Family Aboard The Enterprise, Kirk discovers while undergoing a routine physical in Sick Bay aboard the Enterprise that the reason for his apparent weight gain is that he's pregnant. Justified in that Kirk is a female-to-male transgender person. Kirk decides to continue performing his duties while he's pregnant.
- In chapter 62 of Fallout: Equestria - Project Horizons, a medical scan during a cybernetic upgrading reveals that main protagonist Blackjack is pregnant. It comes as a particular surprise to her because she's still using a contraceptive implant. The medical ponies speculate that Blackjack's Magitek cybernetics saw the implant for another piece of useable scrap material and absorbed it.
- Done more realistically in Mega Man Reawakened. Tron Bonne finds out after 2 months of pregnancy, and tells the other characters soon after.
- Used in Egg Belly, when Konoka gets pregnant by a girl. Apparently, Pactio sex can give even same-sex couples a child. The scene where the doctor tells her this is hilarious.
- In Extended Stay, the Mistress and the Superjail crew find out she's pregnant just when Ultraprison is about to leave. This one is justified since she hasn't been far enough along to exhibit any symptoms.
- A minor character in Red Fire, Red Planet, Master Chief Special Warfare Operator Haellh, mentions to Admiral Riker early in chapter four that she's six weeks along. Her fellow fireteam member Petty Officer Freeman is really surprised by this and complains about her not telling him, but she says she only found out a few hours before.
- It's mentioned in Kill la Kill AU that Ragyou's pregnancies with Satsuki and Ryuuko were these, as, in the case of the former, she didn't found out that she was carrying until she was showing and, in the case of the former, she wasn't prompted to find out that she was pregnant, until someone pointed her being pregnant with Ryuuko out as a possibility, however, the latter is a bit more explainable, as, considering that she had complications as she was giving birth to her oldest (the which almost killed her) and the resulting surgeries, it's possible that, even after she's completely healed, she didn't think she could get pregnant again, let alone carry another to term.
- Ran's pregnancy with her kits in Gensokyo 20XXI, however, probably due to being servile, she didn't know the symptoms and just assumed she was getting fat, until she pieced together why Chen and Flandre were quite eager to forego eating, so she could have their food.
- Minor example in the Distant Finale of Brother on Brother, Daughter on Mother. Eleya mentions in her Internal Monologue that she only discovered she was pregnant with her and Gaara's fourth after he had left for a five-year mission. She's forty at this point, so they may not have thought she could get pregnant again.
- Ryuuko's pregnancy in "Batteries" with Hoshi (or, as she intended to name her, "Esther"), as she didn't know until she had given birth to her.
- In Unexpected Surprise, Ladybug and Chat Noir have sex once and she falls pregnant. What makes it particularly twisted is that 1) neither know each other's secret identities, 2) they soon break up due to Ladybug loving another, 3) they both have to give up their Miraculouses a few days later and 4) Adrien moves to USA at the same time. The result is that, after a six year long absence, he returns to discover there is a girl about whom three people know she is the daughter of Ladybug and Chat Noir, but the only one to have figured out she is the daughter of Marinette and Adrien is Gabriel.
- Triptych Continuum: As insinuated in Tricks of the Trade Show, Sweetie Belle, Rarity's sister, as Rarity learns from her dad:
"We weren't..." An even longer pause. "...expecting Sweetie." Very awkwardly, "Took us a while before we got you, and we kind of thought — you were gonna be it. Sweetie was..." Stopped.
She understood the hesitancy: a father who wasn't comfortable with discussing birth, because it might lead into his child considering the activities between her parents which led to pregnancy. Rarity had an excellent imagination, and thus when matters of self-preservation arose, knew just when she had to shut it down.
- In My Pain, My Thrill, Peach didn't even know she was pregnant until three years after she gave birth. She had no clue that Bowser could impregnate her and she had no signs of being pregnant. As a result, the pregnancy came out as a surprise for both of them. Peach fell into a coma before giving birth and Bowser hid it from her afterwards, purposely avoiding her and denying Jr's claims that Peach is his mother. Peach ends up figuring it out herself after talking to Bowser Jr and noticing their shared genetic trait.
- This seems to be inverted in Secret Sunshine, where Satsuki knew she was pregnant and hid it, making it a surprise to everyone else, with Ryuuko noticing something off (nausea, mood swings, eating more than usual, and "being bigger in the middle") but not putting the pieces together, until she's handed a baby.
- In Amazing Fantasy, Mary Jane Watson didn't realize she was pregnant with Peter's child until after they signed their divorce papers.
- The Monty Python movie Monty Python's The Meaning of Life, previous to the infamous "Every Sperm Is Sacred" song, features a poor Yorkshire family whose mother is having babies drop right out from between her legs as she cooks and cleans for her burgeoning family, with her only reaction being to say "Get that for me, would you, Deidre?" to one of her older children. 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 Water Boys 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 The Blue Lagoon 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.
- It's unclear how long she knew about it, but Addams Family Values starts with Morticia announcing that she's going to have a baby... right now, and being rushed to the hospital for delivery. (The surprise is only within the context of this movie, though, as the Sequel Hook of the previous one had her wordlessly announcing said pregnancy by way of knitting baby-sized pajamas.)
- In Father of the Bride II, Nina winds up getting pregnant at roughly the same time as her recently-married daughter. She initially mistakes the symptoms for menopause. And she is at an age where menopause would be probable, so her surprise is rather more believable than most examples.
- There's a grammar joke that goes like this — the joke being that the periods after each "sex" are menstrual periods.
Sex. Sex. Sex. Sex (Oh, Crap!)
- In A Brother's Price Mother Eldest first thinks it is menopause when she doesn't get her period anymore. She is delighted to find out it is Someone to Remember Him By.
- 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.
- I Know Why the Caged Bird Sings: In a subversion, Maya Angelou relates that she knew she was pregnant, but the surprise was certainly on her family after she hid it from them for eight months.
- Implied in The Fifth Elephant. Even if Lady Sybil wasn't surprised, her husband most assuredly was, him asking stupid questions and her giving dry responses.
- Daisy's mother in The Stone Diaries is unaware that she's pregnant.
- Bluestar in Bluestar's Prophecy, thanks to her one-night stand with Oakheart. She is unaware of her pregnancy until another cat points it out.
- In The Kingdom of Little Wounds, Ava realized she was pregnant after Jacob had already left her. She insists that Jacob ejaculated on her stomach.
- In Dancing on the Edge, it's mentioned that protagonist Miracle's mother wasn't aware she was pregnant for several months since it barely showed until the later months, and since she, as a dancer, was already very thin and implied to be anorexic she wasn't tipped off by her missed periods.
- This happened to Peggy Olsen in Mad Men, such that she didn't know until she went into labor.
- Sonia Branning on EastEnders was the same - she didn't know she was pregnant with her daughter Rebecca until she went into labour. Bear in mind that Sonia was only 15 at the time.
- St. Elsewhere:
- In "Hearts", an overweight woman named Gina Barnett comes into St. Eligius complaining of stomach pains. Upon examining her, Dr. Armstrong discovers that she is not only pregnant but about to give birth. Prior to this, Gina had no idea that she was pregnant. After the baby is born, she abandons it in the hospital as she can't afford to raise a child because she is already taking care of her invalid father.
- In "Lost and Found in Space", an intellectually impaired young woman named Pru Dowler, who has the mental capacity of a seven-year-old, is brought to St. Eligius after sustaining minor injuries in a bus crash. She and Buddy, a similarly disabled young man, spontaneously have sex in her hospital room without really understanding what it means. Pru is frightened by the experience. About six weeks later in "Loss of Power", her mother brings her back to St. Eligius as she is suffering from nausea and stomach pains. Dr. Morrison's tests reveal that Pru is pregnant. Pru's mother blames the hospital for her daughter's condition and insists that she have an abortion, which is performed by Dr. Craig and Ehrlich in "The Boom Boom Womb".
- 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 goes into the ER and not only realizes that she is pregnant, but that she is giving birth to twins. Dr. Benton has 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 is a flat "That's impossible." note
- All My Children's Opal Cortlandt learns she's pregnant after several weeks worth of what she assumed were menopause symptoms. Not to mention her husband's supposed infertility.
- Doctor Who 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.
- Happens in the latest series of Whitechapel when DS Miles's wife fears she might have ovarian cancer only for it to turn out she's six months pregnant.
- At the end of "Baby on Board", Modern Family's third-season finale, Gloria 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 Christmas Episode of Call the Midwife.
- A minor point in the fifth season of Castle. Ryan and his wife are having trouble getting pregnant... because they're already pregnant.
- During one of his much-loathed clinic visits, House meets a woman who wants to know why she's been feeling sick and can't seem to lose weight. House later explains that she has a "parasite", which he can't legally remove after a month. She expresses disbelief since she's been using birth control.
Woman: And my doctor said I might not get any periods at all if it was working...
House: Interestingly enough, you also don't get any periods if it isn't working.
- On Schitt's Creek, Jocelyn Schitt thinks she's going through menopause but is instead pregnant with her second child.
- Dr. Quinn, Medicine Woman chalks up her symptoms of malaise to stress, not pregnancy until her friend Dorothy suggests it. (Rather ridiculous, seeing as she's a DOCTOR).
- Averted in Eric Church's "Two Pink Lines". The young man and woman in the story notice that the woman is two weeks late, so she takes a pregnancy test and the two of them angst over it. The test comes up negative, so she leaves at the end.
- Thomas Rhett's "Life Changes" reveals a real-life example with his wife, Lauren. They had been trying and failing to have a child, so they adopted one from Uganda... right before Lauren actually managed to become pregnant anyway.
- A double-subversion from The Bible: Sarah has overheard three men (actually angels in disguise) telling her husband that he and Sarah will have a son. She laughs because she is old and has been infertile for a long time, and gets 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!)
- 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.
- Played for Laughs in the stage musical of Roald Dahl's Matilda: Mrs. Wormwood is shocked to learn that she's pregnant, despite the fact that she (a) is nine months in, (b) is showing heavily, and (c) has been pregnant once before.
- In The Book of Unwritten Tales 2, Ivo discovers that she's pregnant and is really surprised. In fact, discovering how the pregnancy came to be is her original quest in the game, even if she ends up getting involved in graver matters later on.
- The Golden Ending of Pandora's Tower reveals that this happened to the couple who were intended to be the subjects of Experiment Zero. This threw the entire experiment into imbalance since it had to be a man and a woman only, not a family of three. The husband was ejected from the Experiment but it was too late to save his wife (who went on to become Zeron). Fortunately the Experiment's overseer was able to use the Orichalcos chain to save their unborn child. The husband was left to raise their son by himself. Said son would go on to be Aeron's ancestor. Zeron's spirit is at peace when she realizes this.
- Girl Genius: Apparently when Gil sets out to repair something, he doesn't just halfass it. In addition to correcting Punch's mute-ness and Judy's mis-sized eyes on top of putting them back together and bringing them back too life, he apparently made them... ahem... "fully functional". Witness Maxina Agatha Gilina Heterodyne Clay.
- On The Guild, Clara was well aware that she was pregnant. Her husband, on the other hand, was quite shocked to find out.
- A couple of Amoridere's characters, Toki and Doki. The former didn't know she was pregnant and she wasn't conscious when she gave birth, while the latter found out while she was in labor. This is justified, as the sisters never had babies prior and there's the fact that erin pregnancies aren't overt (along with that they reproduced through parthenogenesis).
- Glorie gives a bit more justification on Toki's end, as, even though she's given birth before, she still delivers the titular baby in her bed, without realizing that she was pregnant, Doki pointing out that her sister isn't always aware of things, likewise, no one noticed anything different about her, mental or physical-wise.
- In this story on Not Always Healthy, the woman is so preoccupied with her son's open-heart surgery that she dismisses her lack of periods, weight gain, mood swings, etc. as stress, until she complains of a stomachache and the nurse realizes she's in labor.
- In Family Guy, Peter looks up one of his old girlfriends; and is surprised to find that since he last saw her she's become very ugly and even fatter than he is. While they're talking, a baby plops out from between her legs, surprising them both. She then yells to her offscreen husband, "You were right! I was pregnant!"
- According to The Learning Channel series I Didn't Know I Was Pregnant, there are a number of reasons for why a woman might have a surprise pregnancy, regardless of whether she's ignorant of real life pregnancy symptoms or highly educated and self-aware. Examples include: a lifestyle-induced lack of periods (whether due to obesity or extremely low body fat), improper contraceptive use, failure to realise contraception is not infallible, doctors not revealing antibiotics can damage contraceptive effectiveness, and spotting throughout pregnancy being interpreted as a normal period. There are several life-long health conditions that have many symptoms in common with pregnancy. Also, body shape, weight, and the way a baby lies can disguise weight fluctuations or result in no visible baby bump.
- 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 Nightmare Nitro.
- Many British women's magazines have Truth in Television versions of this trope on a fairly regular basis. Multiple women have reported giving birth while on the toilet (one example was a teenage girl who had ovulated but not had a period before; another was a woman who, due to how the baby was positioned, didn't at all look as though she was pregnant), having to then cope with the shock of it and having to break the news to their loved ones.
- In 2012, there was news 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 Pregnant Badass, even if she hadn't been aware of it. Justified because the normal signs of pregnancy (lack of periods, stomach pains, vomiting) can be chalked up to the stress of battle.
- In the late 1990s, a woman made the Seattle news after she went to the hospital with terrible stomach pains and delivered a healthy 6-pound baby girl. As her periods had always been light and irregular, and she continued to spot throughout the pregnancy and had no baby bump at all, she had no idea she was pregnant until she gave birth.
- This can happen more often than not, due to pregnancies having symptoms that mimic other conditions (as mentioned in the above instances) or no symptoms at all.
- In one unusual case, a woman didn't know she was pregnant until after she woke up from a short coma and was told that she had given birth. She had a condition that caused her to have two uteruses and didn't know it and didn't stop having periods because of the second uterus. Before she gave birth she began suffering from seizures due to a pregnancy related condition called preeclampsia, and while she was being driven to the hospital a bump in her belly was noticed for the first time which may have been caused by the seizures shifting the position of the baby. The baby was removed by C-section while she was in a medically induced coma and she didn't wake up and learn what had happened until three days later and at first she thought there was a mistake when the nurse brought the baby to her.
- Not a Surprise Pregnancy, but Jonathan and Drew Scott's parents were positive they were going to have a single child. (Ultrasounds weren't commonly done for routine pregnancies at that time, and the brothers' heartbeats happened to be synchronized every time their mother went in for a checkup.) The doctor delivered Jonathan, started out the door on the assumption that he was done here, and was chased down by the delivery room nurse because Drew was on his way.
- In 1939, a then-five-year-old girl named Lina Medina was brought to the hospital in her village of Ticrapo, Peru, for what her parents thought was a large abdominal tumor. It was soon found that she was pregnant, and she was transferred to a hospital in Lima for a C-section. She had been having periods since she was about 3 years old, and her reproductive organs were as developed as one would expect in someone 10 years older than she was. Her father was temporarily jailed on suspicion of incest, but there wasn't enough evidence against him, and Lina wouldn't say who had done this to her.