Wikipedia is your friend here:
Human males do not have the anatomy needed for natural embryonic and fetal development. The theoretical issue of male ectopic pregnancy (pregnancy outside the uterine cavity) by implantation in biological males has been addressed by experts in the field of fertility medicine, who stress that the concept of ectopic implantation, while theoretically plausible, has never been attempted and would be difficult to justify – even for women lacking a uterus – owing to the extreme health risks to both the parent and child.
Robert Winston, a pioneer of in-vitro fertilization, told London's Sunday 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 the bowel – and later delivered by Caesarean section. Ectopic implantation of the embryo along the abdominal wall, and resulting placenta growth would, however, be very dangerous and potentially fatal for the host, and is therefore unlikely to be studied in humans. Gillian Lockwood, medical director of Midland Fertility Services, a British fertility clinic, noted that the abdomen is not designed to separate from the placenta during delivery, hence the danger of an ectopic pregnancy. "The question is not 'Can a man do it?'" stated bioethicist Glenn McGee. "It’s ’If a man does have a successful pregnancy, can he survive it?’"
Since 2000, several hoax web sites have appeared on the Internet purporting to describe the world's first pregnant man. While sometimes relying on legitimate scientific claims, in reality, no such experiment has ever been reported. Fertility clinician Cecil Jacobson claimed to have transplanted a fertilized egg from a female baboon to the omentum in the abdominal cavity of a male baboon 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.
A local... (surgically altered) person has been described in the press as "the world's first pregnant man" but he/she/it turned out to be sort of a hot mess and is currently engaged in a vicious court battle with the mother/father... er other parent/hot mess.