Male pregnancy refers to the incubation of one or more embryos or fetuses by the male of any species. Almost all pregnancies in the animal kingdom are carried by female organisms. In all heterogamous species, the males produce the spermatozoa and rarely, if ever, host the zygote (the seahorse is a notable exception).

The Syngnathidae family of fish has the unique characteristic where females lay their eggs in a brood pouch on the male's chest, and the male incubates the eggs. Fertilization may take place in the pouch or before implantation in the water. Included in Syngnathidae are seahorses, the pipefish, and the weedy and leafy sea dragons. Syngnathidae is the only family in the animal kingdom to which the term "male pregnancy" has been applied.

Pregnancy among intersex and transgender people

Some intersex people with XY chromosomes develop entirely female bodies and, if the individual has a uterus, can gestate an embryo conceived in the lab. The typical karyotype for a male is XY, so in this case the pregnant person has a Y chromosome. Animals too can be intersexed, depending on specificities of the species involved.

Some transmen (female-to-male transgender people) who interrupt hormone treatments can become pregnant, while still identifying and living as male. This is possible for individuals who still have functioning ovaries. Although these individuals have XX chromosomes, from the standpoint of gender identity they are pregnant men.

For example, Matt Rice bore a child in 1999 by artificial insemination during his relationship with writer Patrick Califia. Thomas Beatie, who chose to become pregnant because his wife was infertile, wrote an article about his pregnancy in The Advocate. The Washington Post further broadened the story on March 25 when blogger Emil Steiner called Beatie's pregnancy the first "legal" male pregnancy on record, in reference to the state of Oregon recognizing Beatie as male.Labor of Love website.Thomas Beattie, "Labor of Love: Is society ready for this pregnant husband?", The Advocate, April 8, 2008, p. 24. He gave birth to a girl in 2008. Beatie is now pregnant again, as announced by Barbara Walters on The View.

The possible science of an induced male pregnancy in humans

Since most men lack a womb, alternative measures would have to be made for an nontubal abdominal ectopic pregnancy. Oral doses of female hormones would be administered to the man to make him receptive to the pregnancy. In vitro fertilization techniques would be used to induce an ectopic pregnancy by implanting an embryo and placenta into the abdominal cavity, just under or into the peritoneum. In women, such pregnancies have a 5% viability rate. Once implantation was complete, the man would stop taking hormones, because the pregnancy itself would take over. The embryo would secrete sufficient hormones to maintain its own growth and development. The delivery would require open surgery (Cesarean section) to remove the baby and the placenta. The latter would be the real danger because it forms such intimate connections with surrounding blood vessels that a massive hemorrhage would be likely. Implantation might also involve other structures in the abdomen, including the bowel, and it is possible that parts of other organs might have to be removed. Several physicians who were well-accustomed to advanced and dangerous forms of ectopic pregnancies would have to be on-hand to handle any complications. The real problem with a male pregnancy of this type is not its plausibility, but if the man could survive it, since a man's body is not meant for birth. In women, ectopic pregnancies are generally removed as soon as possible. The fetus would also be in danger of complications because it would be deprived of the protection of a uterus.