Interspecific pregnancy

Interspecific pregnancy (literally pregnancy between species, also called interspecies pregnancy or xenopregnancy) is the pregnancy involving an embryo or fetus belonging to another species than the carrier. Strictly, it excludes the situation where the fetus is a hybrid of the carrier and another species, thereby excluding the possibility that the carrier is the biological mother of the offspring. Strictly, interspecific pregnancy is also distinguished from endoparasitism, where parasite offspring grow inside the organism of another species, not necessarily in the womb.

It has no known natural occurrence, but can be achieved artificially by transfer of embryos of one species into the womb of the female of another.

Potential applications include carrying human fetuses to term as a potential yet ethically controversial alternative to surrogate mothers or artificial uteri for gay male couples, mothers with damaged uteri or straight couples that do not want to risk childbirth. It would also provide a sober, drug-free and nonsmoking carrier that is cheaper than human surrogates. For animals, it could be a valuable tool in preservation programs of endangered species, providing a method of ex-situ conservation. It could also avail for recreation of extinct species.

Immunologically, an embryo or fetus of an interspecific pregnancy would be equivalent to xenografts rather than allografts, putting a higher demand on gestational immune tolerance in order to avoid an immune reaction toward the fetus. Some mice experiments indicate an imbalance between Th₁ and Th₂ helper cells with a predominance of Th₁ cytokines. However, other mice experiments indicate that an immune response towards xeno-fetuses does not belong to classical cytotoxic T lymphocyte or natural killer cell pathways.

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