It’s been a criticism from anti same-sex marriage advocates, and a painful reality for gay couples – two same-sex partners cannot conceive a child which is genetically their own.
But that may not always be the case, there are several scientific routes which would allow same-sex couples to have their own biological children.
In 2010 researchers in the US published a report on a process called in vitro gametogenesis, which they said they had used to produce ‘viable’ male and female mice from two fathers.
In 2015 scientists at Cambridge University in conjunction with the Weizmann Institute of Science created human egg and sperm cells using skin cells.
The process relies on embryonic stem cells – cells which have the potential to become any type of cell – which are ‘programmed’ to turn into eggs and sperm.
Ultimately, the technology would mean a woman’s cell could be converted into sperm cells while a man’s cells could be used to produce an egg. The other partner would contribute their sex cells as per usual.
For Lesbian couples, one of the partners could carry the child. For gay men, a surrogate would need to be found.
Last year, Dr Sonia Suter, examined the social, legal and scientific implications of the research.
“Research on human cells suggests that in vitro gametogenesis with reproductive potential may one day be possible with humans,” she wrote.
“This technology would allow same-sex couples to have children who are biologically related to both of them; allow single individuals to procreate without the genetic contribution of another individual; and facilitate “multiplex” parenting, where groups of more than two individuals procreate together, producing children who are the genetic progeny of them all,” she said.
Dr Suter concluded that the process would be beneficial and preferable to current procedures in some contexts, but substantially more problematic in others. Multiplex parenting was a particularly unique issue.
But on same-sex couples, Dr Suter concluded that 'ethical' concerns were not well founded. In any case, they had been overtaken by reality, with same-sex parents able to adopt children or access current forms of reproductive technology.
The new process could be of real benefit to same sex couples, she concludes, because it gives them legal and genetic certainty – as well as providing a more regular biological structure (ie. Those raising the child are also the biological parents, unlike the case of surrogacy or adoption).
“As long as we countenance other methods of ART [Assisted Reproduction Therapy] that allow parents to form genetic links with their future child, as we have done with dual-gendered couples, equality argues for similar options for same-sex couples or dual-gendered families who cannot benefit from current methods of ART,” she concludes.
But putting the process into practice could be some way off, researchers say.
“The only way to demonstrate the effectiveness and safety of these techniques in humans is to use in vitro gametes (sex cells) to try to produce viable offspring in controlled settings – when and if we deem it sufficiently safe to do so,” Dr Suter said.
The stem cell route may be a superior route than one earlier proposed method, which drew on the experience of cloning.
That process, which was advanced as a possibility over a decade ago, would have removed genetic material from a female’s egg and replaced it with genetic material from a male’s cell.
The potential mixing of genetic material, the fact that it was not a ‘natural’ egg, and concerns over the viability of cloned animals all make that process less than ideal.