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Male pregnancy is the incubation of one or moreembryos orfetuses by organisms of themalesex in some species. Most species that reproduce bysexual reproduction areheterogamous—females producing larger gametes (ova) andmales producing smaller gametes (sperm). In nearly all animal species thatgive live birth, offspring are carried by thefemale until birth, but in fish of the familySyngnathidae (pipefish,seahorses and theleafy seadragon), males perform that function.[1]
The fish familySyngnathidae has the unique characteristic of a highly derived form of male brood care referred to as "male pregnancy".[2] The family is highly diverse, containing around 300 different species of fish. Included in Syngnathidae areseahorses, thepipefish, and theweedy andleafy seadragons. The males of some of these species possess a brood pouch on the trunk or tail; in other species, theeggs are merely attached to the male's trunk or tail when the female lays them. Although biologists' definitions of pregnancy somewhat differ, all members of the family are considered byichthyologists to display male pregnancy, even those without an external brood pouch.
Fertilization may take place in the pouch or in the water before implantation, but in either case, syngnathids' male pregnancy ensures them complete confidence of paternity.[3] After implantation in or on the brood pouch or brood patch, the male incubates the eggs. Many speciesosmoregulate the brood pouch fluid to maintain a suitablepH level for the developing embryos. In at least some species, the male also provisions his offspring with nutrients such as glucose and amino acids through the highly vascularized attachment sites in or on his body.
This period of incubation can take much longer than the production of another clutch of eggs by the female, especially in temperate regions where pregnancies last longer,[4] leading to a reproductive environment in whichsexual selection can be stronger on females than on males due to increased male parental investment. This reversal of usual sex roles has only been found in pipefishes, whereas seahorses have largely been accepted as monogamous.[5] Some pipefish species display classicalpolyandry because of this unique situation. Male syngnathids usually prefer females with large body size and prominent ornaments such as blue skin pigmentation or skin folds. Syngnathid males in some species are apparently capable of absorbing eggs or embryos while in the brood pouch.[6] In these cases, embryos with the highest survival rate are those whose mothers display the preferred phenotype.
Syngnathidae is the only family in the animal kingdom to which the term "male pregnancy" has been applied.[1]
In 2021, Chinese researchers at theNaval Medical University in Shanghai published apreprint of a study that attempted to impregnate male rats, usingparabiosis with female rats. Each male rat was castrated, surgically joined to a female, and given a transplanted uterus. The researchers then implanted embryos in both the uterus of the male and female parabionts. Pregnancies were allowed to develop until two days before the end of a full term, and were terminated bycaesarean section. The researchers studied 46 such parabiotic pairs. In over half of the pairs, neither the male nor female became pregnant with normal embryos; in about one-third of the pairs, only the female became thus pregnant; and in six pairs, both the female and male became pregnant. There were no pairs in which only the male parabiont rat became pregnant.[7] The study attracted much attention and controversy, with some researchers questioning the utility of such research, and others raising questions of bioethics issues.[8][9][10]
In 2023, Japanese scientists used skin cells from 2 male mice to createeggs and fathered a litter of seven babies.[11] The eggs were implanted in surrogate female mice.[11] The current downside is the success rate is 1% (7 mice were born out of 630 attempts).[11] This milestone in reproductive biology was published in British scientific journalNature, cultivating the idea of more reproductive possibilities in the future.[11] The team was led by developmental biologist Katsuhiko Hayashi of the Osaka and Kyushu universities.[11]
Mammalian males, including humans, do not possess auterus to gestate offspring.[1] The theoretical issue of maleectopic pregnancy (pregnancy outside the uterine cavity) by surgical implantation has been addressed by experts in the field offertility medicine, who stress that the concept of ectopic implantation, while theoretically plausible, has never been attempted and would be difficult to justify – even for a woman lacking a uterus – owing to the extreme health risks to both the parent and child.[12][13]
Robert Winston, a pioneer of in-vitro fertilization, told London'sSunday Times that "male pregnancy would certainly be possible" by having an embryo implanted in a man's abdomen – with the placenta attached to an internal organ such as thebowel – and later delivered surgically.[14][15][16] Ectopic implantation of the embryo along theabdominal wall, and resultingplacenta growth would, however, be very dangerous and potentially fatal for the host, and is therefore unlikely to be studied in humans.[14][17] Gillian Lockwood, medical director of Midland Fertility Services, a British fertility clinic, noted that the abdomen has not evolved to separate from the placenta during delivery, hence the danger of an ectopic pregnancy. BioethicistGlenn McGee said "the question is not 'Can a man do it?'. It's 'If a man does have a successful [ectopic] pregnancy, can he survive it?'"[15]
Since 2000, severalhoax web sites have appeared on the Internet[17] purporting to describe the world's first pregnant man. While some rely on legitimate scientific claims, no such experiment has ever been reported. Fertility clinicianCecil Jacobson claimed to have transplanted a fertilized egg from a female baboon to theomentum in theabdominal cavity of a malebaboon in the mid-1960s, which then carried the fetus for four months; however, Jacobson did not publish his claims in a scientific journal, and was subsequently convicted on several unrelated counts of fraud for ethical misconduct.[13]
Transplanting a uterus into a male body poses a challenge due to the lack of natural ligaments, vasculature, and hormones required to support the uterus. The uterus would either have to be donated by a willing donor or betissue-engineered using the male's stem cells and then implanted into the pelvic region.[18] Afterward, anin vitro fertilisation (IVF) procedure would be followed to insert the embryo into the male's transplanted womb.
In 1931, transgender femaleLili Elbe (assigned male at birth) underwent a uterus transplant in an attempt to achieve pregnancy, but died of complications following the procedure.[19][20]
Sometransgender men choose to become pregnant or wish to preserve their fertility.[21] Those with functioningovaries and auterus can become pregnant.Masculinizing hormone therapy reduces fertility and stops themenstrual cycle, but is not considered an effective contraceptive—trans men takingtestosterone may still become pregnant even if their periods have stopped.[21][22] Trans men who undergo somemasculinizing surgeries, includinghysterectomy (removal of the uterus) andbilateral salpingo-oopherectomy (removal of both ovaries) are infertile.
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Hindu religious texts, such as theMahabharata (composition range from 300 BCE to 400 CE) and theVishnu Purana (composition range from 400 BCE to 900 CE), contain the story of King Yuvanashva, who accidentally becomes pregnant by drinking a sacred potion intended for his queens. He proceeds with the pregnancy and his son,Mandhata, goes on to become a king renowned for his greatness, benevolence, and generosity.[23][24]
Inancient Greek religion andmyth, a version ofDionysus' birth (known in mainland Greece after 500 BCE, popularized in 500 CE),[25] claims that Dionysus was sewn into Zeus’ thigh. "So the rounded thigh in labour became female, and the boy too soon born was brought forth, but not in a mother's way, having passed from a mother's womb to a father's."[26] Athena was believed to have been born from the forehead of her father Zeus. The earliest mention is in Book V of theIliad (c. 800 BCE), when Ares accuses Zeus of being biased in favor of Athena because "autos egeinao" (literally "you fathered her", but probably intended as "you gave birth to her").[27][28]
Virgil Wong, aperformance artist, created ahoax site[17][29] featuring a fictitious male pregnancy, claiming to detail the pregnancy of his friend Lee Mingwei.[30][31][32]
Male pregnancy as a trope in fan fiction―calledmpreg―is also commonly explored inhentai, thesubgenre ofspeculativeerotic fiction known as theOmegaverse, andslash (homosexual)fan fiction, usually based upon fantasy series such asSupernatural,Harry Potter, and video game series such asSonic the Hedgehog.[33][32][34]
In 2021,Unicode approved the "pregnant man" and "pregnant person"emojis in version 14.0, and added to Emoji 14.0.[35] However, this came with some controversy, as some viewed it to be "absurd".[36][37][38]
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