An Always Male main character — for obviously biological reasons — gets an Always Female character pregnant, just before leaving to... do whatever. The original version of this is for this to happen during a war movie.
The protagonist has shore leave or something just before shipping out to the war zone, or maybe the war came unexpectedly and he got drafted without warning. He leaves to go off to war leaving behind a pregnant Love Interest. Can be combined with Altar the Speed.
Occasionally even the mother didn't know she was pregnant until after the male leaves, but often the lover left behind will not tell the father because she "didn't want to distract him" or "worry him" — though it's just as common for the father to receive a letter announcing the birth. Usually this letter arrives when the father is in either a prison camp, or in a muddy foxhole while under fire. Something to juxtapose the brutally and ugliness of war with the joy and innocence of a new baby. Expect the father to become stunned and speechless for several minutes, and for his comrades — even the cynical Deadpan Snarker or Drill Sergeant Nasty of the group — to become respectful and moved by the news. A joyful makeshift party might follow. If in a prison camp this has a strong possibility of a Pet the Dog moment for the prison guards.
Sometimes the Love Interest deliberately wanted to get pregnant (this is lampshaded, and then averted, in Since You Went Away). This was a Truth in Television, and in many places still is. It represents the desire of a woman to have something of her lover to keep in case the worst happens to him. Of course, there is also some Wish Fulfillment for the man as well, since he gets to leave a mark on the world though he's going off into danger. A child means that part of him will live on if he dies.
This war movie trope has then been extended to other settings where the Hero has to leave to go risk his life to save the world—or something else that's dangerous but necessary and suitably heroic. This often captures the emotional aspects of the trope but can lead to Fridge Logic, particularly the further away from the war movie setting you get, as you wonder why the father can't at least show up in between his adventures. It can be handled well, though, given enough justification.
Sometimes it's an unimportant minor character that gets pregnant, and it doesn't have any long-term repercussions whatsoever (for the story and the father that is). He probably doesn't even know she got pregnant; because she's just so considerate she decides not to tell him. In that case, his blissful ignorance neatly evades any and all of the inconvenient Moral Dissonance of being an absentee parent.
There has always been some Values Dissonance with the trope, and it has become increasingly so with the shift in values in the West. That doesn't change the trope from being an expression of strong silent desires held by both men and women.
Sometimes the woman's existence is Retconned so that the main character can suddenly have a son, since of course a hero sires a male heir. In this case, see Luke, You Are My Father. Glorified Sperm Donor is another form this can take, and if the father dies it may overlap with Her Heart Will Go On. Compare My Secret Pregnancy.
- At the start of the Buu saga of Dragon Ball Z, we see that Chi-Chi has a new son named Goten. Apparently, she became pregnant with him sometime during the Android and Cell sagas before Goku was killed by Cell's self-destruct.
- One Piece. Gold Roger got Portugas D. Rogue pregnant with Ace soon before he was captured. Rogue managed to stay pregnant for over a year as to make sure her child would actually be born.
- Inverted somewhat in the anime Bokurano when Chizu Honda is found to be pregnant after she has gone off to save the word via giant mech. Her lover, who is also her teacher, ends up being the one left behind and alive. Not that the jerk deserved it.
- In Fushigi Yuugi, Hotohori and Houki have been married for about a month, and Hotohori needs to go fight Nakago and his army. Meanwhile, Houki is pregnant with Hotohori's son Boushin. Nakago kills Hotohori, so he never gets to meet his son while he's alive. As a ghost, however, he does.
- A different take on this appears in Gunslinger Girl. Hilshire has a hospital preserve some eggs from his cyborg Triela, who due to her limited life span won't live long enough to have children. He leaves a letter with his girlfriend Roberta informing her of this before the Hilshire/Triela fratello leave on their last fatal mission. Roberta carries and gives birth to the child, eventually revealed to a girl named Speranza, though it's not certain if her father was Hilshire himself or an anonymous donor.
- In the manga Mademoiselle Butterfly, by Ogura Akane (who also created Kanojo Ni Naru Hi), Butterfly and Chinatsu have only recently found out that she is pregnant with their first child before he is drafted into the army. Later on, Butterfly comes to suspect that she's having twins, leading to Chinatsu's very amusing response to her letter asking for an additional name. When her husband is reported to have been killed in action five years later, they seem to be an example of Someone to Remember Him By, only he was actually MIA four years after they were born and later turns up a little over a year later, still alive, thanks to some locals.
- The origin of Peter Quill, the legendary Star-Lord, from Guardians of the Galaxy is based on this trope. His father J'son accidentally crashed into Earth while fighting a war and was discovered by Earth born woman Meredith Quill. After some explanations were given, Meredith let J'son stay in her house until he could completely repair his ship. During this period, they fell in love with each other. Then, one day after they consummated their relationship, J'son decided it was time to leave and continue his war. Meredith tried to get him to leave with her but J'son refused as he believed she was going to be safer on Earth. After he left, Meredith realized she was pregnant with J'son's child, Peter.
- X-Men: In the "Fling" story, Colossus was seduced by girls who had the expressed intent of getting pregnant, and he objected on the basis that he couldn't stay to be a father. They told him children were raised by the whole tribe and they really did want his babies because he was obviously good breeding stock. (OK, it wasn't quite that bad.) So the writers went out of their way to avoid the implication of the (young and idealistic) character acting without consideration for the consequences.
- Teased with The Flash. The one-nighter clearly thought that the kid was Flash's—understandable, since the baby's eyes flashed with lightning. She died before she could tell Flash (and might not have for she respected his current marriage to somebody else). Then it turned it out was actually the Weather Wizard's. Awkward.
- At the end of the Superman arc New Krypton, Mon-El gets trapped in the Phantom Zone again, and his girlfriend Jamie reveals to her great-uncle, the superhero Guardian, that she's pregnant right as they're skipping town.
- In ElfQuest with that bit about "leaving a kid behind so in case I die, there will still be something of me left." Skot said this shortly before his death. Basically, to the Go-Backs, life was just doing what you could for as long as you could, and then having a kid who could keep going after you. It was described visually as a person walking through the snow, then collapsing, and another person carrying on from that point... a little depressing, but solid enough as a belief.
- This pops up in Child of the Storm:
- The first time, it's mostly as a throwaway reference - Bucky Barnes and Minerva McGonagall got engaged during the war, and she only realised that she was pregnant after he fell to his presumed death. That child turned out to be the mother of Clint Barton - and yes, it's that kind of fic. However, it gains some additional significance after Bucky resurfaces as the Winter Soldier.
- It's used again, this time as a key plot point, in chapter 75, after a good deal of hinting, it is revealed that Carol Danvers is the descendant of Steve Rogers and Peggy Carter, her grandmother (Steve and Peggy's daughter) having been conceived shortly before Steve wound up crashing the Valkyrie. There was no reason for him to know (even Peggy had no idea), as is repeatedly pointed out to him, but he still feels horribly guilty over it. Also, practically speaking he's still only in his late twenties. He thus avoids and tacitly rejects Carol, who's unsurprisingly rather hurt by this (what with having a shortage of good father figures). In time, he gets over it and they become very close.
- A third time, in the sequel, it's referenced as having happened about a thousand years ago when Thor's magical contraception (which he started getting after 'the Hela Incident') ran out earlier than he expected to, and he was called away to fight a war for a few decades. When he got back, he found that he'd had a daughter, Torunn Thorsdottir, and that while she'd inherited a degree of the strength etc (and became a travelling monster-hunter, because that's what the House of Odin does for fun), she hadn't inherited the lifespan, and had thus died while he was away. He was deeply unhappy about that, to put it mildly (though they did meet when he visited her in Helheim, because she's a Valkyrie and Thor is absolutely crazy enough to visit the land of the dead), and Harry speculates that it's why he was so furious when he found about what he'd missed with Harry.
- Cabin Fever: Promises To Keep follows on from Paul and Marcy's whirlwind affair with an alternate story line in which Marcy survives, unknowingly carrying Paul's lovechild. Although Paul does not survive, Marcy resolves that his memory and legacy will live on in his daughter, whom she names in honor of both Paul and their mutual friend, Karen.
- In Pirates of the Caribbean: At World's End, after the final battle and Will and Elizabeth's wedding, the pair spend the day together and he gives her his heart before he sails away as captain of the Flying Dutchman. The movie's Stinger reveals that, ten years later, he returns to find that he has a son.
- In Sailor of the King Captain Richard Saville and Able Seaman Andrew Brown are in for a shock and Lucinda Brown is going to have some explaining to do.
- In the original Yours, Mine, and Ours the father ships out to sea only to learn that another child will be added to their family, his son Joseph John.
- Pearl Harbor ends with Rafe holds a dying Danny in his arms, telling him he can't die because he's going to be a father. With his dying words, Danny tells Rafe to raise his child for him. Rafe does raise Danny's son whom they name Danny.
- Subverted in Taking Lives. Angelina Jolie plays an FBI agent trailing a serial killer. The morning after sharing a night of passion with the only witness to any of the killer's attacks, she discovers that her one-time lover was, in fact, the killer himself. He manages to evade the authorities yet again and Jolie is fired for getting poked by the man she was supposed to pinch. Cut to the final act where we see her some months later, with a very big belly. Psycho loverboy suddenly shows up in her isolated cabin, hoping to build a happy family with her and their lovechildren. After a brief struggle, the killer stabs her in the womb. Only then is it revealed that her whole pregnancy was faked, because she knew he would come back to her if he thought she was carrying his child.
- Species is about a hot blonde human-looking alien looking trolling L.A. for a human mate to impregnate her. Several unsuitable candidates who never get to close the deal get killed along the way. Eventually she gets spermed by the science geek. She feels the conception taking place while still straddling the guy, and then kills the babydaddy, too. Minutes later, she gives birth in a sewer.
- Species II plays this theme in the exact opposite way. A male alien goes around planting his seed in every woman that takes his fancy. They all die moments after being impregnated, by the alien baby that literally explodes out of their belly, leaving creepy Daddy to take care of them in his creepy barn.
- The end of Species II and start of Species III re-reverses the concept yet again, where the main character knocks up the sexy female alien, before dying in the climactic fight. Though is seems like he kills her after doing her, the final shot of the movie shows her belly expanding to pregnancy-size. This is resolved in the sequel when the mother comes back to life and gives birth to a pure-breed alien baby, before being killed herself.
- Downplayed in Revenge of the Sith, as Anakin finds out he's going to be a father before Luke and Leia are actually born. He accidentally gets Padmé pregnant while on leave from the Clone Wars before having to go fight in the Outer Rim. Padmé presumably didn't find out until after he'd left and had no way of contacting him, not to mention she has to keep the pregnancy secret because Anakin's not supposed to be fathering kids with his secret wife. When he returns to Coruscant several months later she informs him she's pregnant; although shocked, he's overjoyed by the news, insisting it's the "happiest moment of [his] life." The happy times don't last.
- Defied in Harry Potter and the Deathly Hallows: After Lupin and Tonks get married and Tonks gets pregnant, Lupin learns that Dumbledore sent Harry on a secret mission and offers to go with him to assist him in whatever he can, Harry refuses and tells him that his wife and son are more important and leaving them would be an act of cowardice. Lupin storms off but realizes that Harry was right and spends the rest of his time with his family.
- In Robert A. Heinlein's Time Enough for Love, nearly every single female member of Lazarus Long's forty-third century family sleeps with him in order to get pregnant prior to his departure on a Time Travel trip back to early 1900's Kansas City, Missouri. They feel certain that he is going to "get his ass shot off" in that primitive era, and want Someone to Remember Him By.
- Harry Keogh's wife falls pregnant at the end of Necroscope, but he doesn't find out until the sequel (when he's already dead).
- A variation on this happened in Myst: The Book of Atrus: Atrus' mother dies giving birth to him, and his father Gehn leaves for the ruins of D'Ni, cursing his mother Anna as he leaves, who ends up raising Atrus in his stead.
- Played with in an Apprentice Adept book by Piers Anthony. It has been prophesied that Lady Blue will have "a son by two" — her second husband — so protagonist Stile marries her just before going off to do something dangerous, leaving the marriage (temporarily) unconsummated as a little extra insurance for his survival. It works.
- In The Night's Dawn Trilogy, notorious womanizer Joshua Calvert uses a business trip to a planet with self-imposed limits in technological and social progress to seduce and deflower the teenage daughter of his business partner. After he leaves the planet again, she finds out she's pregnant and he finds out he does not forget her as easily as his other affairs. Both are greatly chased around by the plot, so for the majority of the trilogy the trope applies. Fortunately for them said plot seems to wrap up quickly enough that they are reunited even before the pregnancy is immediately recognizable.
- A genuine wartime version of this trope occurs in Margery Allingham's Albert Campion series. Campion marries his longtime fiancée just before going overseas for three years of dangerous intelligence work. He is overcome by a strong emotion nine-tenths pure embarrassment when he finally gets home to Amanda, to discover a small, blond person not quite three years old playing in front of his home.
- In A Song of Ice and Fire Eddard Stark got his new wife Catelyn pregnant before riding off to fight in Robert's rebellion. When he returned she presented him with his son, and was rather less than pleased to discover that he'd brought another one home with him.
- Revan (a sequel to Knights of the Old Republic) has this happen to the titular character and Bastila before he heads off to Sith space, never to be seen again.
- In Simon Hawke's The Wizard Of novels, Merlin Ambrosius is freed from the tree Nimue trapped him in 2000 years ago. When he's killed fighting the Dark Ones, his ghost finds itself drawn into Billy Slade, last descendent of the child Nimue bore after seducing him.
- In the third book of Lynn Flewelling's Nightrunner series, Seregil speculates that he may have done this to one or more women during his stay with the Dravnians in the previous book. In Dravnian culture it's considered good fortune (due to their isolation and presumably limited gene pool) if a woman gets pregnant by an outsider, and Seregil, who was slightly uncomfortable about it, only slept with them to comply with the tribe's bizarre etiquette and preserve needed diplomatic relations, but there's still a certain amount of Values Dissonance bordering on What the Hell, Hero? when considering his casual attitude about the whole thing after the fact, and his total lack of curiosity about whether or not he actually does have any half-Dravnian descendants running around.
- Stargate SG-1: In "A Hundred Days", a stranded Jack O'Neill ends up Going Native and becomes engaged to a local woman who wants a baby with him. At the end of the episode, he's rescued and returns home, leaving her behind gently touching her belly. Word of God stated that they did want the readers to guess that she was pregnant, thinking to pick up the story at a later date. However, they later changed their minds and scrapped the plot.
- In one Hercules: The Legendary Journeys episode, a reunion of old school heroes visits a training academy and one of the older heroes is casually introduced to his daughter. Of course since the mom was an Amazon, her lack of a father growing up was completely unremarkable and not a source of angst to anyone but him.
- Happens in Farscape's season 2 in the "Look at the Princess" episodes. The pregnant mother is stuck for the next 80 years or so in a kind of unaging stasis which Crichton cannot undergo anymore, so at least he's got a (ridiculously) good excuse. Before leaving Crichton tells them to present the royal councillor, who the Princess is actually in love with, as the father so at least someone will be around to help raise the child.
- Charmed: After spending half a season fighting against his duties as an Elder, Leo finally decides to leave the sisters to join the Elders after a near death experience that nearly cost him and Piper their lives. Guess who's pregnant at the end of the episode and what the real identity of the Whitelighter that appeared at the end of last season is? Playing true to the trope, instead of using this as a reason to bring Leo back, no matter how easy it would be for him to visit anyway, Piper and even the grown up Chris insist on not getting Leo involved.
- Baywatch episodes "Baywatch Down Under (parts 1 and 2)". One of the lifeguards discovers that an Australian woman he married and later separated from had a son without telling him. She withheld the information because she knew that if she had told him, he would have felt obligated to stay with her.
- This trope is Emma and Henry's backstory in Once Upon a Time, albeit with the slight twist that Henry's father didn't so much just leave as spectacularly betray Emma before either of them knew she was pregnant, and Emma doesn't keep the baby, but instead gives him up for adoption. It's eventually revealed that Neal had a good reason for doing what he did, and mother, father, and son are all eventually reunited...only for the plot to rear its ugly head and start inventing other ways to keep them apart.
- In Castle, Castle's father was a spy who slept with his mother before being sent on a new mission, which is why they never met until years later.
- ER's Carol discovers that she's pregnant several weeks after Doug has resigned in disgrace and left Chicago.
- In Tommy, Captain Walker impregnated his wife Nora before shipping out to the War.
- In King of the Hill, Cotton had an affair with a Japanese nurse after shipping home from World War II; she seems to have been the only woman whom he actually loved, as opposed to merely sleeping with. He comes back decades later to apologize for having to leave without saying goodbye, and sure enough learns that he has another son (who looks remarkably like Hank).