To twin or not to twin? That is the (unasked) question

A recent spate of articles celebrating the birth of an IVF 'twin' five years after her brother (1, 2, 3, 4) left me perplexed. Why was this news, when embryo freezing has been in use since the mid-1980s? And as the children were not identical by what definition were they twins?

For the first question, I still have no answer. However, thinking about the second brings up a number of issues relating to the reconfiguration of kinship via assisted conception which the articles could have raised, but didn't.

The press called the children 'twins' because, like naturally-occurring fraternal twins, they were produced from the simultaneous fertilisation of two separate eggs. In this sense, twinship is based on the technological mimicry of a natural process.

However, if we consider all the fertilised embryos created from a single cycle of egg retrieval we would logically be talking about more than twins. In this case the two children become quintuplets, as the cycle produced five embryos. And what about two embryos conceived in the same Petri dish, but carried by different women? Where one couple offer their 'spare' embryos to another, would those two children be separated twins? Both scenarios lead us into areas which are deeply uncomfortable.

At the other end of the process, twins may be understood as any two children carried and delivered in a single pregnancy, regardless of the method of conception. Some do use the term 'IVF twins' to distinguish these from naturally-occurring fraternal twins (several of the articles used quotes around 'twin' as well) but this usually describes IVF children born at the same time.

The need for such distinction is interesting and suggests that on some level, IVF twins are indeed understood as different from others — as singletons twinned through gestation and simultaneously as ordinary siblings who just happen to be born together. Indeed, technology means the two children need not even be genetically related. If fertilized embryos from different donors are implanted simultaneously would they still be considered twins? Which are the twins in the Drewitt-Barlow (5, 6) family: Aspen and Orlando, split from the same original embryo, but born four years apart; or Aspen and his sister Saffron, simultaneously gestated but fathered by different men?

Thanks to the legal concept of 'intent' the act of purchasing gametes and/or the services of a gestational surrogate is enough to establish parenthood without requiring adoption. Similarly, it may be that we rely on a tacit concept of 'intent twinship', where children intended to be twins are considered so, and those gestated separately are not. This does, however, beg the question of why embryo splitting is illegal in most countries, when such a procedure — as long as both embryos are implanted at once — would mimic the natural process of twinning as closely as any other permutation discussed above. And still leaves me wondering why a routine IVF birth was considered news whether we call the children 'twins' or not?