Males from just a few animal species, namely seahorses and some of their relatives, are known to get pregnant. New research, currently published as a pre-print awaiting peer review, documents the first recorded instance of a male mammal giving birth from a transplanted uterus.
In the study, male rats were surgically prepared to nurture a transplanted uterus with embryos. The project yielded a low (under 4 percent) success rate, but the male rats delivered pups via C-section that grew without any reported complication. While some have excitedly associated the experiment’s success with the possibility of human application, the lead researcher has repeatedly pleaded online to not associate the study with potential male human pregnancy. Regardless of such prospects, this paper has gained tremendous attention for its ethical ramifications.
The procedure and the results triggered an avalanche of tweets questioning its ethics. Scientists debated whether the scientific progress justified the invasiveness of the procedure — for it to work, the male rat was surgically joined to a female rat so that they shared a circulatory system (called parabiosis). One scientist raised concerns on whether this study is indicative of science turning into an entertainment business, according to reporting in Nature. The lead researcher responded by reassuring that, “[the] animals did not have any painful symptoms such as screaming during the entire experiment” and asked that people “... please don’t bring non-scientific factors into scientific research.”
Aside from the sensational outcome of the paper, it also highlights that male rats' pregnancies were only successful when attached to a pregnant female and that the rats sometimes carried abnormal fetuses.
The paper only has a short discussion section where the potential implications or usefulness of the study is outlined. It reads: "...our findings reveal the potential for rat embryonic development in male parabionts, and it may have a profound impact on reproductive biology research."