The Pregnant Man in the 21st Century
The idea of a man becoming pregnant and delivering a baby has been discussed for ages, and even with science and medicine advancing rapidly in the last several decades, a biological man still has not delivered a baby. The case in the news of a "man" getting pregnant and delivering a baby is more than what meets the eye. The person in question was likely biologically a woman with ovaries and a uterus and merely changed her appearance cosmetically-removal of breasts (which are not required for getting and maintaining pregnancy) and considered herself a man psychologically. Movies such as "Junior" are also taking a great deal of literary license to get around real biological problems of a man getting and maintaining pregnancy to birth.
The idea that a "man" can become pregnant and deliver a baby has to be met with an understanding of biology and medicine. Furthermore, the idea has to be discussed with a dose of caution and skepticism in the sense that first, one must decide what the definition of a "man" is and whether the pregnancy and delivery is a result of a natural phenomenon or the result of specific and extensive intervention medically and biologically. There could be circumstances whereby technically a person proclaimed or designated as a "man" could become pregnant with or without intervention such as in vitro fertilization (IVF). For example, a genetic female with 46 chromosomes with two x sex chromosomes (designated medically as 46,XX) could have extensive external reconstructive surgery to produce male genitalia and remove her breasts but if she still retains her own eggs and uterus and later if "she" wanted to become pregnant could still do so with medical assistance, including IVF. Furthermore, if a genetic 46 XX female had a particular form of PCOS (Polycystic Ovarian Syndrome) she might even have hirsutism (facial hair, a heavy moustache, etc.) and elevated testosterone giving her a more pronounced masculine appearance that some people might misconstrue as her looking like a man and therefore assume that she was. Then there are the cases of babies born with ambiguous genitalia and the physicians might decide with the parents consent to "decide' the sex of the child and alter the genitalia accordingly, even though the internal reproductive organs and the genetic make-up might be contrary to that decision. Then there are the very rare cases of female pseudo-hermaphrodites and hermaphrodites. In the case of psudo-hermaphrodite, a patient who is born with 46 XX chromosomes (genetic female) with what appears to be normal ovaries and a uterus but the external genitalia might be large enough to be misconstrued as masculine genitalia, even to the extent that the urethra traverses the external genitalia and the child might be raised as male. In one form of psuedo-hermaphrodite, called testicular feminization, a child is born genetically male (46, XY) but the body has a defect in the androgen receptor mechanism with the result that the external genitalia are female at birth and there may be rudimentary or absent oviducts and ovaries but there may be the presence of testes which may be surgically removed at birth. These patients may not know their true condition until at an age when they expect menstruation and seek medical advice or when they enter certain sports events and a test reveals their true genetic determination. In case of true hermaphrodites, the individual will have both testicular and ovarian tissue, the external genitalia are ambiguous and the person may appear to be female or male. Then there are patients that have mosaicisms-two or more variations of karyotypes in their bodies-some cells contain one genetic make-up while other cells have a different genetic make-up. These are just a few examples of the means by which a person considered a "man" could indeed be a candidate for becoming pregnant. So it is difficult to say a "man" can never become pregnant and deliver a live baby. There are many other examples that occur in the medical literature of patients with genetic variations or mutations that lead to unusual circumstances that could also lead to the idea that a "man" can become pregnant and deliver a baby.
So aside from the remarkable genetic variations that would favor a person designated as a "man" to become pregnant and deliver a baby, could a man who has fathered a child naturally be able to get pregnant himself and carry a baby to birth? The short answer is: it would be extremely difficult for a biological man to "become pregnant", even if an embryo were transferred into his body. The most important aspect of pregnancy after conception of an egg (oocyte) with a sperm is the implantation of an embryo. Without a uterus, the embryo must find an alternative area of the body to implant. In the case of a man as a "host", human intervention would be required to fertilize the oocyte with sperm in a lab, then surgically transfer the embryo to the body of a man since he would not likely have a uterus! The uterus is "designed" to both nourish an implanting embryo and limit the development of the placenta-a fine balance controlled by fine control of various hormones, communication of the embryo/fetus with the maternal tissue, proper development of the blood supply and the interaction of the two immune systems- any disruption or poor development could lead to rejection at any time. If the fetus/placenta is not properly controlled, the placenta could overtake the body and create a life-threatening situation to the "host"-tapping into the blood supply and destroying tissue as the placenta invades host tissue. Embryos that implant outside the uterus are considered ectopic pregnancies and rarely survive to birth-and if allowed to continue are delivered only by surgical delivery (Caesarian). Indeed, ectopic pregnancies are almost always terminated before they result in the death of the mother. So a man would in essence have to have an ectopic pregnancy. With current technology, even if a uterus were transplanted to a man, the medications required to prevent graft vs. host condition, that is to say, rejection of the foreign tissue would most likely also kill the fetus because implantation and development of the fetus is an ongoing battle of the immune system. Rejection by the immune system can still occur throughout pregnancy. Giving hormones to a man to maintain pregnancy would help, but again, the uterus is an anatomical and physiological wonder that is best for the developing fetus.
The bottom line is, if you take a man that has fathered a child naturally without any intervention or alteration and attempt to get him pregnant, there are many obstacles. Nonetheless, it would not be a surprise if an enterprising and reckless person or group of persons would attempt such an endeavor if not only to prove it can be done but also to garner headlines. At this time, it is fraught with danger and the possibility of failure given the biological constraints in trying to get a true biological man with functioning testes and no uterus to become pregnant. The prevailing philosophy in the medical profession is to provide patient care but also to do no harm, including trying to avoid procedures that might put the patient in a dangerous predicament. But unfortunately there are exceptions to this philosophy of medical care throughout history. When we hear of stories of a man becoming pregnant, we should at first be skeptical given the nebulous nature of the definition of a "man", genetically, biologically and psychological. And if we are involved as a society in attempting to get a biological man pregnant we should put aside the humor in the endeavor and be cautious with the understanding that under certain conditions, a person identified as a "man" could become pregnant but that there could be repercussions when extensive medical intervention is involved.