George and Amal Clooney

Are they ready for the challenge of twins?

George Clooney – Oscar-winner, coffeepod spokesperson, recipient of countless “world’s sexiest man” awards – has just joined another exclusive club. He and his wife this week announced the arrival of their twins, Ella and Alexander.

So well done, George and Amal – you’re in. In fact, you’re in an even rarer substratum of parents who have had boy and girl twins. It’s an elite little group to which I also belong. But even as I welcome these A-list newcomers, it is time to break the bad news: the demands are going to be immense, and with boy/girl twins there are additional challenges, too.

Opposite-sex twins are often described as “hidden” twins. When you tell people you’re having twins, they imagine two little boys or girls in a pram, dressed in identical outfits. When you have one of each, suddenly perceptions shift.

“With same-sex siblings, people will know they are twins. In the case of boy/girl twins, there won’t be the same awareness. You may be asked about them – but not nearly as often,” says Delyth Raffel of Twins UK.

Our twins, Fiona and Cathal, turned four last month. An entire night’s sleep is no longer a pipe dream (infant twins, naturally, take it in turns to lie awake bawling). Lunch and dinner are relatively civilised, with nobody flinging food or concluding that what this party really needs is an impromptu pee under the table.

There is certainly a sense of striking a jackpot with daughterand-son twins – in one swoop, you’ve completed the perfect set. But at other times it can feel like they have been sent to test you.

Boy/girl twins account for one third of all fraternal (non-identical) twin births, and roughly 3,000 are born each year in the UK. However, research into opposite-sex twins is sparse, with scientists more interested in the identical variety.

Of the research that there is, one slightly worrying finding by the University of Sheffield is that male twins can reduce their sister’s fertility due to testosterone crossing the membrane barrier in utero. A study of Finnish church records from the 18th and 19th centuries found that female opposite-sex twins surviving to adulthood were 25 per cent less likely to have children and 15 per cent less likely to get married. Another study, from Columbia University in 2002, found that opposite-sex twins have a 50 per cent higher chance of developing same-gender attractions in adolescence.

But if having boy/girl twins has made one (arguably controversial) thing clear to me, it is this: some gender differences are hard-wired. As Fiona (the senior twin by five minutes) and Cathal have grown out of toddlerhood, what is striking is how utterly different they are. Far from being peas in a

They’re not peas in a pod – more like a pineapple and a kumquat

pod, they more closely resemble two random items from the fruit and veg section – a pineapple and a kumquat, say – that happen to have been thrown into the same trolley.

Certainly, the cliché that girls are more enthusiastic learners holds true for my offspring. I am reluctant to call Fiona more “advanced” than her brother, but she takes instruction with greater readiness and basks in the approval of grown-ups. We recently attended her first ballet show at a small theatre. She adored the applause and beamed from ear to ear. In the stalls, Cathal was torn between wanting to nod off and doing backflips on his fold-up chair.

Also, Fiona has – and I use this word with extreme caution – become more stereotypically girl. Unprompted by us, she carries a baby doll with her everywhere, at night placing her in her cot (shoebox) at the end of the bed.

First-time parents: George and Amal Clooney, left

She has also developed a fondness for ponies and sparkles and the Frozen soundtrack.

Emotionally, she is more forthcoming, too. The twins attend playschool twice a week. The instant she is back in the car, Fiona provides an extended debrief of the day’s events. Cathal might tell you that he fell and banged his knee, but good luck getting anything more from him.

One positive with having opposite-sex twins, however, is that they are less likely to be defined – by themselves or others – by the fact that they are twins.

“A girl who has a brother or a boy who has a sister is going to develop a completely different set of friends,” says Raffel. “You want your children to become mature and independent of each other. Obviously you want there to be a special bond – but you want all of your children to have a bond. With twins, you want them to develop apart so that they have their own identities. With boy/girl twins, this is obviously easier.”

Until a few days ago, I had never really given any extended thought to George Clooney (as one of the few people who paid to see Batman and Robin, I feel like I’ve done my bit). But I will confess to a shiver of empathy upon learning he and Amal have had boy/girl twins. It’s a unique experience – one that will open your eyes to the degree to which children, from the very start, are fully realised personalities. After just a week, the marked differences between our two were clear. No doubt he and Amal will be noticing the same small signs in Ella and Alexander over the coming days.

The excitement, as every parent understands, is knowing that they’ve only just started revealing who they truly are and that every year will bring fresh joy and new surprises. Synchronised pooping is just one of them.