A stock plot. The pregnancy of an adolescent girl who hasn't finished her education, maturation of body and mind, and isn't in a stable relationship (don't expect the dad to stick around if he's similarly young). The actual age at which the pregnancy isn't an issue anymore varies according to these factors.
This trope is usually the result of adolescents fooling around without protection or not fully understanding the biology and mechanics at work, though in particularly dark works, it may be the result of rape. Another possibility is if the girl became pregnant from the very first time she had sex, driving home the message that even a single night of indiscretion can have consequences.
The typical fictional teenager generally tries to hide her pregnancy from her parents for as long as possible, which never actually equates to when she starts looking visibly pregnant. This may ultimately result in a Prom Baby. When hiding it from others besides the parents see Stigmatic Pregnancy Euphemism.
Since Status Quo Is God, most earlier works will have the young mother suffer a Convenient Miscarriage or else put it up for adoption. If this is a soap opera, you can count on the child returning to find his or her real parents as soon as he or she reaches adulthood, which usually takes about ten years. This can even affect shows that don't have long enough runs to see the teenage mother grow up, as an adult character can be revealed to have given up a child for adoption as a teenager.
Another option to avoid scandal is for the girl's parents to raise their grandchild as their own, and the baby grows up particularly close with their "big sister." This will lead to no shortage of angst all around when the truth inevitably comes out. More recently, however, abortions are becoming a solution, although this is still rare. Even more recently, there's been a trend toward keeping and raising the baby, although this is hardly exclusive to very recent works.
A very common reason a character might be a Tragic Dropout.
Sadly Truth in Television, to many, many girls. This has become MTV's primary show content.
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Anime and Manga
Played straight in Bokurano. A girl who's Hot for Teacher gets led into a trap and gang raped by his friends, getting her pregnant. (This had to be Bowdlerized in the anime, where she doesn't get raped but her asshole teacher/boyfriend stil screws her over badly and gets her rep totally smeared.) She then unknowingly signed her life away when she agreed to pilot a Humongous Mecha, as it drains her life energy entirely once she uses it; unfortunately, that means her baby also dies. She goes on a rampage, killing those who raped her, and almost kills her teacher when she is stopped by her sister, whom he was dating and she protects him and attempts to calm her down via telling her "Go Through Me"; the girl calms down enough to destroy the enemy, and then she and the baby die. It is later revealed that her baby counted to the number of pilots piloting the mech, meaning the group was one short — and if the baby had been called to pilot, they all would have been doomed. It should be noted that the girl in question is in middle school, so she can't be older than fifteen.
The manga Akkan Baby is about this. It's the farthest thing from an angst-fest though.
In Digimon Tamers, Ruki's mother Rumiko had 10-year-old Ruki when she was 28. She was actually only a few years younger than her mother, apparently had her around 21 (she's 49). She somehow managed to find (or keep) a career as a model.
Utilized in the 3rd Fushigi Yuugi OVA. Miaka (age 18) married Hot Teacher Taka Tsukunami Tamahome reincarnated after graduation, and she is 3 months pregnant with her first child. The baby is transferred out of her body and into that of a 16-year-old named Mayo Sakaki, Taka's pupil, who wants Taka all for herself, while poor Miaka falls into a coma. It is the Shinzaho needed to summon Suzaku and save the Universe of the Four Gods. Furthermore, it was subconsciously given to Mayo by Miaka, not stolen by Mayo, even though it seems that way at first. The baby is then returned to the mother, and later Miaka gives birth to a healthy baby girl named Hikari.
In Sakende Yaruze! Shino and Misao think they want to have kids at 17. When Misao does get pregnant, she leaves Shino so as not to wreck his future, not telling him about it and giving birth to Nakaya alone. 17 years later, Nakaya and his girlfriend have a pregnancy scare, but luckily for Nakaya she was just a little late.
The main character Yukino Miyazawa in Kare Kano. She and Arima started to be sexually active when in highschool, and Yukino got pregnant in their last HS year. They got married after graduation and, due to economic problems, Yukino herself remained a House Wife for a while; when her older daughter Sakura and the Half-Identical Twins that followed were more or less grown, she went to college and became a doctor.
An extreme example provides the main plot of Kodomo no Kodomo, where both parents are in fourth grade.
Shaman King: Hana Asakura was born when his parents, Yoh and Anna were 16. There's a scene of them sleeping together fairly early in the manga which is heavily implied to be when he was conceived. This was fan speculation in the original series, but Shaman King Flowers confirmed it.
From the New World: We last see Maria and Mamoru when they are 14 and 12 years later, it's revealed they have a child who was born shortly before they were killed. The child appears to be a preteen.
In One Piece, Scarlet was apparently only 16 when she had Rebecca.
In Haré+Guu, Hale is 10 while his mother Weda is 24. It's the reason she lives in the jungle: Her city family kicked her out.
Kodomo no Omocha: Sana's birth mother Keiko was fourteen when she gave birth. And it's implied in the manga that Sana was the product of sexual abuse, as apparently her dad was Keiko's uncle. It also would've been borderline statutory rape, since the age of consent in Japan is in between 13 and 18 depending on the prefecture, and this means Sana was conceived when Keiko was 13.
Atsuko Urameshi from YuYu Hakusho gave birth to Yusuke when she was just 15.
Banji's mother in Go Nagai's Delinquent In Drag (Oira Sukeban) gave birth to Banji in her early teens, explicitly stated in dialogue.
Card Captor Sakura: Sakura's mother, Nadeshiko, married at sixteen, and gave birth to her eldest son Touya a year later.
In Digimon Tamers, some maths will reveal that Ruki's mother Rumiko had her when she was eighteen.
The dub changed Ruki's age without touching Rumiko's, so if we go by All There in the Manual, latter gave birth at fifteen instead. However, in the actual series, Rumiko did say Rika was the product of her being married before she was ready, so eighteen is still the youngest she could have been.
Her grandmother is also very youthful-looking at least.
That, and two of the kids are twin girls no older than three. The third child is actually born in that same Distant Finale.
Hinagiku and Yukiji's adopted mother in Hayate the Combat Butler looks to be rather young to be the mother of 28-year old Yukiji, a little more probable for 12-years-younger Hinagiku, especially recently, but she's still nearly alarmingly young to be their mother. That she's the Katsura's adopted mother doesn't make things that much better, especially when considering that Mr. and Mrs. Katsura had apparently been trying to have children of their own for years beforehand.
Mikoto is stated to have had Wataru when she was young (and there's implication that Nagi's mother also gave birth while she was young) and actually left Wataru in the care of his maid Saki because of it. Mikoto still looks young despite having a 13-year-old son.
Rosario + Vampire gives us Kurumu's mother Ageha and Mizore's mother Tsurara, both of whom appear to be in their early thirties; the anime reveals them to have been classmates. Justified in Tsurara's case, since Yuki-Onna go sterile at a very young age, and as a succubus, Ageha probably didn't want to take things slowly either.
Marine Gabrielle de Polignac in Rose of Versailles, who had her eldest daughter Rosalie at age 14. She gave her away to her former maid Nicole, who took the baby away and raised her as a peasant. For massive irony, Polignac's carriage ran Nicole over several years later, killing her...
Karin: When Kenta was born, his mother was 16 and his father was 19.
In Gundam SEED Yzak Joule's age is given as sixteen. His mother, Ezalia's age is given as thirty-three. This means Ezalia was seventeen when she had Yzak. Given her country's aggressive pro-birth policies, this actually makes a lot of sense.
In the Lyrical Nanoha franchise, Lindy Harlaown was 17 years old when Chrono was born, and is 31 during the first series. Though she still looks like she's in her early twenties at most, and doesn't visibly age for the next decade either.
Fruits Basket: Since she got married not long after middle school, Kyoko probably had Tohru when she was 16 or 17, at most.
Played for all it's worth in Bitter Virgin, where the female lead was raped by her step father from the age of 12 and got pregnant from him twice, the first ending in miscarriage and the second born and adopted out right away.
In Love Is In The Bag, Lulu Mennella is shown to be quite youthful, and her age is toyed with but never revealed.
In Angel Crush, it is hard to believe that Vera Willow is already a mother of three. Serena Oak is revealed to be Lulu Mennella's older sister in her crossover appearance in Bag Together from Love Is In The Bag. Exactly how much older is not revealed, but when Serena is standing side-by-side with her teen daughter Sandy, they look quite similar.
Irisviel von Einzbern is a Happily Married mother who looks like she is in her early twenties. Her daughter, Ilyasviel, looks like she is five, at the very most. During the main storyline of Fate/Zero, Irisviel's age is around nine when her daughter is eight. Justified, as they both are homunculi whose distorted growth rates make them look older and younger than they actually are, respectively.
In Batman supporting character Stephanie Brown, also known as the Spoiler, realized she was pregnant during the Cataclysm storyline, and was temporarily Put on a Bus until the kid was born. She decided to Give Him a Normal Life and give the kid up for adoption, and even asked Robin not to tell her the gender of the kid so she wouldn't get attached.
Irony perhaps? A character named Spoiler not wanting to know the gender?
Raquel from Icon found out she was pregnant right around the time her superhero career began. Unlike Steph she decided to keep her son, whom she named Amistad.
Lisa in Lisa Is Pregnant is said to be older than in The Simpsons, since Maggie is old enough to talk, but is unlikely to be much older, and thus would presumably fall into this trope.
Towards the end of Fullmeatal Alchemist: Forever Edward and Winry's daughter, Amy, is impregnated by her childhood friend, Maes Mustang.She is twelve.
This is the premise of the Avatar: The Last Airbender fanfic Iris. Although, it's a slight variation, as the characters involved are considered adults in the Fire Nation despite being seventeen. The stigma comes from the fact that their kid would be illegitimate.
This sappy Star Wars fanfic: Forever In My Heart, actually has a very explicit sex scene at the beginning, but turns out to be a relatively good read. And seeing from this site, Ahsoka getting "preggers" is pretty popular.
The New Retcons had this as a plot point: Elly had had one of these, and her greatest fear is rejection if everyone learned about it, a fear realized when her daughter Claire finds her and John attacks Elly in response. Word of God is Connie Poirier had one too, and that was how she and Elly met: they ended up at the same school for wayward girls.
Discussed at length in "Dear Sweetie Belle", with Rarity describing having fallen into this situation- while technically of age, she had just started fashion academy and was in no way prepared to deal with a foal on her own. Her parents, having just lost a foal themselves, agreed to raise the foal as her sister, i.e. Sweetie Belle.
Juno carries to term while arranging an adoption for her child. In a Gender Flip of the "first time" variation, Paulie Bleeker was the one losing his virginity.
There's also Jenny, Juno, which features a more comic version of a Korean teenage couple working through the girl's pregnancy, despite serious disapproval from parents on both sides (the girl's older sister even suggests that they send to baby to their other sister in the USA - who was pregnant at about the same time - so that the other sister could claim to have had twins).
Mary is a bit of a subversion, though, since she obviously understands how she got pregnant—she just doesn't understand why God let it happen when she fully thought she was doing his will.
In Sugar & Spice, Diane Weston (Marley Shelton) is a popular high school cheerleader whose life revolves around her boyfriend Jack (James Marsden) and cheerleading, as she is the captain of her school's "A-Squad". However, when Diane becomes pregnant by Jack, her life falls apart as her parents disown her. She moves in with Jack, and the two quickly get jobs, but Diane quickly realizes that Jack lacks the financial skills to provide for her and their child. Diane confides to her fellow cheerleaders about her problems and the group come up with a way for Diane to make the money she needs: robbing banks.
Gertrude Baniszewski told her ward Sylvia Likens in An American Crime (based on the true crime) that she had her oldest daughter Paula at a young age. Paula herself gets pregnant by her cheating boyfriend (though somehow doesn't show after months have passed). Gertrude is unable to deal with the thought that Paula made the same mistake she did, leading her to blame poor Sylvia and ultimately torture her to death.
The B-plot of Peacock deals with Cillian Murphy's character negotiating with the mother of his child, a teenage prostitute played by Ellen Page, in her third movie on this page.
Played for laughs in the second Hairspray movie. The plot of the movie is set in motion when The Corny Collins Show holds a casting call to replace one of their dancers. How long will she be out? "Oh, about nine months..."
The main character in North Country has her son at age 16 after being raped by her teacher.
Parodied in Don't Be A Menace To South Central While Drinking Your Juice In The Hood, where the father of Ashtray (played by Shawn Wayans) is played by Lahmard Tate, who is about a year younger than Wayans. This is a Running Gag through the entire movie, with things like Ashtray reminiscing about changing his father's diapers, and going to a party his dad is too young to attend. This was poking fun at the fact that Lawrence Fishburne, who played the father of Cuba Gooding Jr's character in Boyz n the Hood, is only about seven years older than Gooding.
Slam, with the slight variation of being told from the (also) 16-year old father's point of view
Mr. and Mrs. Bo Jo Jones the baby was stillborn, the couple breaks up for a few months and then get back together. At the epilogue, they've been married for three years.
Push by Sapphire: The main character actually has two children, one when she was 13 and another when she was 16.
Bumped by Megan McCafferty, where only teens can get pregnant due to a virus making adults infertile. Teens are paid big bucks to be surrogates for couples. It creates a never-ending cycle, because the teen girls have all their kids for other people and when they are mature enough to have kids, they can't so they hire surrogates...and so on.
In Aunt Dimity: Detective, this is revealed to be the reason Prunella Hooper was able to blackmail Peggy Taxman. Peggy was fifteen when she met a brash young American serviceman, and she had his baby shortly after he was killed by an exploding piece or ordinance leftover from WWII. She is reunited with her son over fifty years later.
Bella from Twilight gets pregnant with her daughter at age eighteen.
In Fifty Shades of Grey, Grey's mother was presumably this (she was in her early twenties and he was four when he was taken from her, meaning that she likely would have been between fifteen and eighteen). This is never remarked upon.
Fortune's Rocks by Anita Shreve. As it's set at the turn of the century, 16 year-old Olympia is forced to give up the baby for adoption by her parents.
Livorette in Madame d'Aulnoy's Fairy TaleThe Dolphin is sixteen when she gives birth to a son after the protagonist Alidor impregnates her. The child is conceived out of marriage. Alidor himself seems to be around Livorette's age.
Giovanni Francesco Straparola's Fairy Tale "Pietro Pazzo" (also known as Peter the Fool) takes this trope further by having the title character impregnate a ten-year-old princess, who gives birth at the age of eleven.
In Pretty Little Liars Emily ends up pregnant after losing her virginity to Isaac and had the baby over summer while staying at her older sister's
Gender inverted in The Wild Hunt Trilogy. Judith's father was 14 at her conception, due to him being the only male around at a time when her 28 year old mother desperately needed to get pregnant.
In the Kate Thompson book Children of the Night, the teenaged protagonist's mother was only 14 when she had him. He realizes that his father, who he never knew, must have been an adult, as she would have told him if his father was a classmate of hers. This squicks him out, as the idea that an adult could take advantage of a young girl like that is inherently disturbing.
Gender reversed in The Shipping News, where the protagonist calculates that his grandfather must have been about 11 when he fathered a child. His aunt's reply is simply: "You don't know Newfoundlanders."
Several examples in the works of V. C. Andrews. Notably, Dawn in the Cutler series was 17 when she gave birth to Christie; Leigh Casteel had Heaven at age 13-14 (the books waver on this since the last two were finished by a Ghost Writer) and Celeste in the Gemini series is around fifteen when her daughter is born.
In Clan Of The Cave Bear, Ayla is eleven when she has her son Durc - her sister Uba isn't much off that when she gets pregnant. Justified in-universe in that the Clan have a lifespan of about thirty and go through menopause in their early twenties, and so have children early, and Ayla was held to their standards.
In Ginger Pye, Jerry and Rachel's mother married their father at the age of seventeen, at a time when such marriages were unusual but not unheard of. Their grandmother is still quite young, and they have a three-year-old uncle, affectionately referred to as "Uncle Benny" by everyone in the neighborhood.
In the Books Of Swords, it is outright stated that the Silver Queen, Yambu, became pregnant with Ariane while still barely a teenager herself. As such, when Ariane is in her early twenties, Yambu is still only in her mid-thirties or so.
The age when men are married and expected to start servicing their wives, in A Brother's Price, is sixteen. But only a generation ago, that age was only thirteen, and the Moorlands were fathered by a boy who was married off at that age. Cullen Moorland expresses relief that the age of marriage is higher now.
In Moonlight Mile, the sequel to Gone Baby Gone in the Kenzie and Gennaro Series, Patrick and Angie eventually track down Amanda McReady, a girl who went missing when she was four years old and then disappeared again when she was 16. She has a baby with her that she claims is hers because of this trope. It's not actually hers, but rather her friend Sophie's, who does actually qualify for this trope since she's the same age as Amanda.
The Maeve Binchy novel Evening Class has a young girl realizing that her older sister is actually her mother and that all of her "cool big sister" gestures were actually her going all out to be the best mother that she could possibly be despite her limits. She's the result of a teen pregnancy.
Danielle Steel frequently trots this one out, with all of her forty-something female characters frequently being said to look more like their children's older sister, thanks to them having had their children in their early to mid 20s.
Sweet Valley High: Descriptions of the characters will almost inevitably include the mention that the twins' mother Alice is often mistaken for their older sister (she's presumably only in her late 30s/early 40s given that she and the girls father met their senior year of college).
And the father looks like an old version of their brother.
Degrassi The Next Generation had Manny get pregnant in high school and have an abortion. Unsurprisingly, this two-part episode didn't air in the US on the first run.
Later, Liberty gets pregnant and carries the baby to term, though she puts it up for adoption after breaking up with the father (who was perfectly willing to take responsibility, but it ended up leading him to have a breakdown.)
Mia was an unwed teenage mother on the show, earning her the nickname 'Mamma Mia'.
Degrassi has covered every option for a pregnant teen. They began with Manny's controversial abortion, moved onto Liberty dealing with giving up her baby for adoption, and then they show the trials of model/teen mother Mia Jones in later seasons who kept her child. Emma has also dealt with a pregnancy scare, and Anya tries to get pregnant to keep her Muslim boyfriend Sav from inevitably leaving her for his arranged wife. Jenna (who provides the page quote) attempts to raise her baby before giving him up for adoption. 18 year old Dallas has a 3 year old baby he left with the baby's mother. Degrassi is like a pamphlet. They cover all the bases.
That's not getting into Degrassi High, where Erica and Tessa both got pregnant. Both got abortions. The only difference is that Tessa's baby daddy is Joey Jeremiah. In some instances, Erica's pregnancy created a minor What Happened to the Mouse?, as the second part of the episode was not broadcast.
Hot In Cleveland had an episode revealing that Joy had given a child up for adoption when she was a teenager.
Beverly Hills 90210, Adriana gets pregnant, can't have an abortion when she goes because it's too late, wants to keep it but eventually puts it up for adoption. Harry also didn't know that his high school sweetheart had a kid and put it up for adoption until he moved back to LA.
Grange Hill was the first British soap opera to tackle this in 1991.
Coronation Street also tackled the subject with Sarah-Louise Platt getting pregnant. In 2014 the soap took it a step further by giving 12-year-old Faye a pregnancy storyline.
It even managed a twofer: Vicky Fowler, whose mother was 16 years older than her, became pregnant herself at the same age.
Kat Slater/Moon is discovered to have given birth to Zoe at age 13 after being raped by her uncle.
Gilmore Girls - Lorelei got pregnant at 16 and had Rory, and the main plot of the show is about their relationship as two girls living alone together without a very big age gap.
Rory's ex-boyfriend Jess was also the product of one, which contributed to his Troubled, but Cute backstory.
A past plot on Neighbours was about a teenage girl who got pregnant and wanted to put it up for adoption, but the child's father wanted custody. They eventually get back together and decide to keep the baby.
Quinn on Glee, which ends up as a major problem for her as not only is she president of the school's celibacy club but has never had sex with her boyfriend. The father is actually his best friend, Puck.
Izzie on Grey's Anatomy had a daughter at sixteen and gave her up for adoption.
One episode had the police find a newborn baby in the dumpster behind a middle school. The doctors treat the baby and spend the rest of the episode trying to figure out who the mother is. Four suspects were taken to the hospital, while their parents all denied their own child was the mother.
A running gag on The Steve Harvey Show as never-seen character Tameka is in Cedric's third-period health class, has two children, and is always available to assist with child-rearing questions.
Zandra, Salene and eventually Amber also get pregnant on this show (although Salene miscarries and Zandra dies before her baby is born ), which is weird because these four are the four original older female mall rats.
Private Practice, as if it didn't already have enough drama, has quite a few of these the biggest one being Sam and Naomi's daughter Maya's teen pregnancy, which includes getting married to the father of the baby.
Reba opens with this issue in the characters' mind, though not the only issue.
Jal in Skins, although she aborts it. Mini in the third generation of Skins and she keeps it.
An episode of Masters Of Horror directed by John Carpenter has a teenage girl get raped by an alien and has to go have it aborted. Her father (Ron Perlman) and brothers attempt to stop it and in the end, the baby alien ends up saving her life by killing her father.
Justin Suarez from Ugly Betty is the result of this. Hilda had him in her senior year of high school after getting pregnant at the prom.
Used several times (unsurprisingly) on 7th Heaven. Most notably averted, however, when the Camdens' daughter Mary turns up preggers, but she denies having had sex when confronted by her parents. It was a clerical error at the doctor's. The real pregnant person was Mary's mom Annie, pregnant with the Camden twins.
Carla's friend from Scrubs. Elliot accidentally offended her by assuming that her son was a boyfriend, when in actuality she had him at age 14.
Both Katherine and Isobel from The Vampire Diaries gave birth to daughters as teenagers who were given up for adoption (although, as noted in the article above, teenage pregnancy as a concept did not really exist when Katherine gave birth to her daughter in 1490). In her case the scandal is because she's not married.
The protagonist of Life Unexpected is a 16 year old girl that was never successfully adopted that seeks emancipation. She was conceived during a one-night-stand her parents had at their winter formal in high school.
Also the premise of TLC's reality show, High School Moms.
In the Mexican TelenovelaQuinceañera ("15 year old girl"), the main theme around Thalia's character Beatriz was her how she got pregnant at age 15.
A comedian on BET's Comicview joked about having a young mother: "My mama was fourteen when she had me. You know what that was like growing up? When I was a kid I'd be struggling with my homework, she'd be at the other end of the table struggling with her homework, neither one of us can play outside till we're finished..."
In The Borgias, Lucrezia is married at 14 and has her first child, Giovanni, at around 15. While early motherhood was common back then, this particular situation was fairly unusual even then and dangerous for the health of both mother and child.
Best Player featured the mother of a 16-year-old dating a 30-year-old. No mention of an age difference in the couple was made... so... How old was Chris's mom when she was born?
Tanya, the lead character's 18-year-old daughter who has a three-year-old son in Single Father. The circumstances surrounding the child's conception (who the father is, etc.) are left unstated, but it is heavily implied that estrangement from her father as a teenager contributed to the pregnancy.
In the Doctor Who episode "The Doctor Dances", we discover that Nancy is Jamie's mother rather than his sister as she claimed, and would have given birth to him between the ages of 14-16. Adding to that the fact she doesn't look older than twelve.
Exaggerated in Raising Hope: Virginia and Burt are grandparents in their late 30s/early 40s, having had their son Jimmy in their mid-teens (15 and 17, respectively). Jimmy himself is just outside this trope having had Hope in his early 20s. Virginia's mother had her at about twenty, leaving her to be Raised by Grandparents. Jimmy's great-great grandmother was revealed to be alive in one episode, dying at 104 years of age while her own daughter was in her eighties, so she also counts.
Speculated to have happened offscreen in Mighty Morphin' Power Rangers due to Power Rangers Samurai involving Skull's 15-ish-looking son Spike. If we assume that each season takes an actual year, he came along when Skull had just graduated high school at the oldest. Of course, we don't truly know Spike's age, or who his mother is, let alone how old she was (though it's a different brand of Unfortunate Implications if she was of age when Skull wasn't.)
Madonna's song "Papa Don't Preach" is about a teenage girl who wants to keep her baby and confronts her father about it.
In Smash Mouth's "Nervous in the Alley," a 15-year-old runs away from home because she's pregnant.
"Rock'n'roll Lullaby", written by Barry Mann and Cynthia Weil, recorded by B. J. Thomas. The lyrics says:
"She was just 16 and all alone
when I came to be
so we grew up together
my momma-child and me"
John Hiatt's "Good as She Could Be" is about a woman who had a baby at eighteen.
Lisa in Funky Winkerbean got pregnant and gave the baby, a son, up for adoption way back when, back before the first time skip.
Before she died, Lisa was able to reunite with her son, revealed to be Darin Fairgood.
Mrs. Walker at the beginning of the 1993 musical of Tommy, who is pregnant at age 16 during World War II.
In Romeo and Juliet, Juliet's mother says she was already a mother at Juliet's current age (nearly 14) in justification of Juliet's Arranged Marriage with Paris. Which was normal... back then, as girls from rich families got married around that age to cement alliances, and also so they'd have as many kids as possible and not be a burden for their parents. Poorer women would marry later (around 23 or older), as they and their possible suitors would take far more time to gather enough money for a decent-sized dowry and household, and legally male and female apprentices could not marry until they completed their indenture.
Heather from Silent Hill 3 is pregnant... for some reason, carrying an unborn god inside her womb. And she does not look like a pregnant woman at all.
In the bishoujo game Ko-ko-ro... 0, Kasumi Kuonji is revealed to be one in one of the possible endings of the game. Her baby's name? Souji. Yes, Kasumi, originally presented in the original Ko-ko-ro... as being Souji's older sister, is possibly his MOTHER.
Leisure Suit Larry: Love For Sail has Nailmi and Wydoncha Jugg, a mother-and-daughter pair of country/western singers who look almost identical. This being Leisure Suit Larry, the game hangs a lampshade on this, implying that Nailmi gave birth to Wydoncha at an improbably young age.
Fire Emblem: Genealogy of the Holy War has a few first-generation parents (or potential parents) who are very young, such as Sylvia and Dew. It's not incongruous with the medieval setting, though.
Same goes to Fire Emblem Awakening, where kids no older than 15 (like Lissa, Ricken or Donnel) are said to become parents. While in most cases it's due to their children having come from the future, a few potential pairings result in this occurring normally.
Joel from The Last of Us. He had his daughter Sarah before he could go to college.
While not mentioned directly, in Apollo Justice: Ace Attorney, we know from near the beginning that Apollo was abandoned as a baby and we later find out his mother is Thalassa Gramarye. If you work out the ages (Apollo is 22, she is 40), she would have been 18 when she fell - probably part of the reason her controlling father made her give him up.
Seems to be very common in Clannad or just Key's works in general. Tomoya's mother gave birth to him shortly after marrying her husband. His parents married when his father was still in school.
Seems to run in the family. Nagisa gets pregnant shortly after marrying Tomoya, though technically she's not a teen, but around 20 (the age of majority in Japan).
Sakura's mother in Kare wa kanojo. She was seduced and impregnated by her then-teacher.
In Umineko: When They Cry, Beatrice Ushiromiya, first introduced in EP3 as the Beatrice from 1967 is revealed to have had this. She was in fact Kinzo's illegitimate daughter with his secret lover Beatrice Castiglioni, but her mother's Death by Childbirth drove Kinzo into such despair that he eventually deluded himself into believing that she was her mother's reincarnation, and it's all but outright stated that he raped her, making her pregnant with a Child by Rape at a young age.
In The Overture Vanessa Olsen was married at twelve and had a son eight months later. Her son is now seventeen and she is barely thirty.
Meg has a pregnancy scare in the episode "Peter's Daughter".
And then there's the song "Prom Night Dumpster Baby".
In The Simpsons episode, "Little Big Girl", Bart dates a girl named Darcy who shortly reveals that she is one of these. The father is apparently a Norwegian exchange student, who went back to "Norwegia".
Daria has Jane Lane's older sister Summer. Word of God puts Summer in her early thirties or so and she has four kids, and two of her kids seem to be preteens.
Foxxy Love is implied to have something like this trope with her kids.
At one point a member of Foxxy's family shows up and looks to be about 14 or 15. He introduces himself as being Foxxy's grandson. So unless Foxxy is just way older than she looks, both she and her own kids must have their kids at very young ages.
Doughy Latchkey's parents Karl and Kim on Moral Orel both look and act like teenagers. They were shown to be in high school with Stephanie 12 years ago, so they probably had Doughy not too long after that.
Although this is a very common occurrence in real life, a famous example is Melissa Drexler aka "Prom Mom".
Sarah Palin's eldest daughter, Bristol, had a baby at 17 during her mother's campaign for pregnancy in 2008.