- 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.
- 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.
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- This State Farm commercial has the wife dropping the bomb on her the husband, after he said he doesn't want another baby, while he's scrubbing a crayon drawing off a wall.
Anime and Manga
- 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 .
- 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 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 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 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 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 Setsuna 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.
- The Monty Python movie Monty Python's The Meaning of Life, 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, 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:
Sex. Sex. Sex. Sex (Oh Crap!)
- The joke being that the periods after each "sex" are menstrual periods.
- 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.
- In a subversion, Maya Angelou relates that she knew she was pregnant in I Know Why The Caged Bird Sings, 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, and his stupid questions and her dry responses are particularly hilarious.
- 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.
- 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 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.
Live Action TV
- This happened to Peggy Olsen in Mad Men, 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 St. Elsewhere.
- 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."
- 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.
- Happened in the latest series of 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", 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.
- 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.
- 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.
- In Family Guy, Peter looks up one of his old girlfriends, who's turned ugly and obese in the intervening years. Then a baby splatters out from between her legs, much to their mutual surprise. Though she then calls to her husband/boyfriend/lover/something offscreen "I was pregnant!" Implying that she did suspect, or was at least open to the possibility.
- On The Guild, Clara was well aware that she was pregnant. Her husband, on the other hand, was quite shocked to find out.
- 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: infertility, 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.
- 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 delivering 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.
- 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 pregancy (lack of periods, stomach pains, vomiting) can be chalked up to the stress of battle.