14/08/2014 12:49 BST | Updated 22/05/2015 06:12 BST

They're Twins, You Know

Yes, they're twins.

Usually when I say that to someone what I get is a puzzled look. People struggle to comprehend. They pause, unsure what to say.

You don't often get twins born two and a half years apart you see.

Although these days, with more and more kids being born as a result of IVF, this is getting more common. You see, although my kids were born two and a half years apart, they were "made" at the same time.

When you undergo IVF treatment, you do some very wacky things to your system. Daily injections drive a massive stimulation of your ovaries, which then release a number of eggs during your monthly cycle, rather than the single egg that would be produced in a "normal" cycle.

These eggs are then mixed in some way with your husband's sperm to fertilise and produce embryos (for traditional IVF they're just put in the same petri dish and left to get on with it, whereas in our case the geekdaddy's sperm could not be counted on to even manage that and so we underwent ICSI where a single sperm is injected directly in to each egg). Typically the embryos mature in the lab for 3 days, and then a number (usually one or two) are implanted into your womb through a procedure that is uncomfortably like a cervical smear.

As I said to my husband at the time, it's a very strange way to get pregnant.

News broke recently that there have now been over five million successful live births as a result of IVF pregnancies since Louise Brown made history when she was the first one born in 1978. Five million. Five million little miracles, just like my two.

There are millions of couples worldwide for whom this was the only way we could have children, who are astonished by what can be done with science these days. And for me, and I suspect many other women in the same position, it has had a lasting effect. For example now, almost 5 years after her birth, I'm not 100% sure of the geekdaughter's birth weight. It was either 8lb10 or 8lb12, but I can never remember. However I remember all the numbers associated with the IVF cycle that gave her to us without hesitating.

Eleven eggs collected. 9 fertilised. 4 frozen immediately. The remaining 5 were given three days to develop, after which time 2 were transferred, 2 were frozen and 1 failed to develop. Net result 2 embryos in me, 6 in the freezer in the lab.

Only one embryo implanted, but 9 months later, thanks to the miracle of science, the geekdaughter arrived.

When we'd finally got over the shock, and felt like we were getting the hang of this whole parenting lark, we undertook a second IVF cycle, this time using the embryos from the freezer rather than making more new ones.

Four embryos defrosted (it's standard procedure to defrost two at a time, so actually what happened was that the first pair were taken out, neither of them survived the thaw, so a second pair were taken out. From this pair one survived and one didn't). That single embryo was transferred back into me, and 9 months later the geekson arrived.

It was our fertility consultant who first said the word "twins" to us. We were sitting in his office after my first scan in my second pregnancy, and he pointed out that the new baby would be the geekdaughter's twin. At which point we probably did the puzzled, blank look we see so often in others when we talk about this subject.

"Twins? Really?" said the geekdaddy "I guess that's pretty unusual"

"Not really" said the consultant. He was a man of very few words, so didn't elaborate. My experience has been that it is still fairly unusual, backed up in part by newspaper articles like this one which tell us how unusual it is.

Of course the crux of the matter is that it all depends how you define "twins", and again this is one of those questions that's only arisen since the development of IVF treatment. Do we define twins as "two children conceived at the same time" or "two children born at the same time"? Until IVF was available there wasn't a difference, but now of course, as in our case, there can be. And although I love the story of how our two children were conceived, I don't think of them as twins. They weren't born at the same time, and I certainly haven't faced the challenges that parents of "real" twins experience in raising them. So whilst I enjoy telling the story about my kids being twins, I don't think of them that way myself. They are brother and sister, and that's good enough for me.

Ruth Arnold is a geeky, tech-loving wife and mother of two (aged 5 and 3), trying to juggle working part time with running the home and organising the family. When she gets any spare time she likes to share tech tips and family milestones on her blog at Geek Mummy.
Twitter @geekmummy