Published: Thursday 09 August 2018

Submitted by Professor Karen Thorpe, Institute for Social Science Research, The University of Queensland

Professor Karen Thorpe dissects the myths and realities of twin children’s lives …. Are twin children more likely to have developmental problems? Is being a parent of twins more stressful? Are twin relationships problematic? Do twins have problems making friendships? To separate twins or not at school? Professor Thorpe shares some surprising discoveries from her research.

This blog is based on a video presentation by Prof Thorpe which can be viewed here


Twins on average spend less time in the womb – yet they’re more resilient. Parents, grandparents, or people who work with twins know this and the other many strengths and difficulties experienced by twins and twin families.

Twins also have risks and challenges unique from singletons. In addition to the biological risks during pregnancy and birth, there are several social risks for twins and their families: twins can encounter developmental delays, families’ burden of care is doubled and the twin relationship itself presents potential challenges as well as many benefits.

So how do these risks map out into the reality of being a twin, and for their families?

Myth or reality: Are twin children more likely to have developmental problems?

After taking extreme adverse events out of the picture, we see - particularly in the early years of life - some differences between twins and singletons in language development and attention deficit.

Research I conducted with psychiatry researcher Sir Michael Rutter found a mild difference in performance of twins compared with singletons on verbal and nonverbal IQ and language. We only looked at children born beyond 32 weeks to exclude those children who are born very preterm to control for “high risk” obstetric factors. We then looked at medical records and observed social interactions. The patterns of family interactions, not biological complications, explained differences in IQ and language ability.

We also tracked children across the period of language development, from 1–3 years of age, in the Avon Longitudinal Study of Parents and Children. Using very detailed video analysis we tested these children, we observed them in their homes and in their interactions with their siblings and parents. At 20 months of age, and again at 36 months, we found that twins were lagging behind their single-born counterparts in terms of language.

What we discovered also confirmed what was previously reported: that identical male twins and identical twins had the highest risk for language delay, but that it was still mild. And when we followed up these children into their school years, that delay resolved, so that the developmental difference between these twins and their peers disappeared.

So there are mild increases in risks for developmental problems among twins, once you exclude those who were born preterm or small for their pregnancy length. These mild delays are attributable to the differences in the early social environment, the care burden on parents and disruptions. What’s important in both cases is that there’s something we can do to prevent or remedy the problems because they’re about the social environment.

Myth or reality: Is being a parent of twins more stressful?

Two major studies have looked at whether being a parent of twins is more stressful. My very first publication in twins’ research was an analysis of a birth cohort of 17,000 families in the United Kingdom that compared twins, closely-spaced single-born children and widely spaced single-born children, to look at differences to mothers’ mental health.

When the children were five years of age, we found the higher the care burden, the more likely a mother is to experience depression. So if you have an only child, you have a lower care burden and the lowest risk of depression. But if you have twins, you have a higher care burden and are at higher risk of depression.

In addition, a more recent study, found mothers of multiple birth children at nine months of age to be 43 percent more likely to have moderate or severe depression, compared with mothers of singletons. The highest rates of depression were amongst families who had a child with a disability and amongst those whose children were born very preterm. These families are dealing with a whole range of additional issues compared with the normal care burden of caring for a young child. Their care burden in the first year of their children’s lives is very high.

When we followed up families in the Avon Longitudinal Study of Parents and Children, we found support seemed to drop off in the second half of the year of having a multiple-birth child, coinciding with the time the children became more mobile. Where support dropped and children became more demanding, depression went up. This emphasizes the need for interventions to focus on providing additional supports – and to monitor families over that first year of life.

So yes, there is a higher care burden for all parents of twins and multiples, not just when there are obstetric and perinatal complications.

Myth or reality: Are twin relationships problematic?

DZ bubbles

So what about twin relationships? Are they problematic? In my research, I’ve certainly seen strengths as well as challenges in multiple-birth families. Strengths include closeness, which twin relationships offer opportunities for. But if the relationship becomes very close, it could be excluding, and it could be a disadvantage. So what do we see here?

Hypothetically, as a twin, the best place to be in your identity, is to be balanced between your twin and multiple-birth self. We took on this hypothesis to see if very closely-coupled twins existed in a study of twin children in Perth and Brisbane that we conducted in collaboration with Professor David Hay.

We asked parents and teachers about the relationship between the twins, but also spent an extensive amount of time observing co-twins in their preschool classrooms and in their first school year. We found no reported examples of extreme individuals, and very few close-coupled twins (which made up about two percent of our sample). Some relationships were mixed between close-coupled and mature connections. As we tracked twins over time, the number who were close-coupled went down to one percent and everyone else had a balanced relationship. However, each pair in this one percent who remained close-coupled, when followed up in year three at school, had a clinically significant behavioural difficulty in one or both of the multiple-birth children.

We also observed these children in their preschool year to see if we could see a close-coupled relationship. For many, we couldn’t. Twenty percent spent most of their time separately, although they were in the same classroom. In some, we observed engagement but then they separated. Interestingly, only two percent of our children in this sample exclusively engaged together. And all those children had marked developmental disorders.

There were no differences in rates of behavioural problems between twins and single-born children. It appeared that conflict, not closeness, in the twin relationship predicted problems. We found conflict between twins, just as we do in singletons when we look more generally at the population. What is different between twin and sibling relationships is that twins are together more. The twins I followed were in their early years, from birth through to about 5–8 years old. So we did see more conflict, because there’s more opportunity for it, but not high levels of conflict. It’s only when you get unusual levels of conflict that you have problems – the same as for single-borns.

Myth or reality: Do twins have problems making friendships elsewhere?

What about the relationship between twin children and other children? One of the concerns that’s very often raised is whether the twin relationship causes twins to have problems making friendships elsewhere.

We’ve looked at this extensively and we find when twins enter school or childcare, they may have slightly less friends than single-born children. There are a range of things that might explain this. First, it’s hard to get a childcare place for two children at a time, so they may enter later. And, when they’re very young, they may want to stay together. But once they enter a group-based setting – childcare or school – that difference in the number of friends disappears.

However, twin children are more likely to share their friends, and the more genetically similar you are, the more friends you will share. So identical twins will share far more of their friends than non-identical twins. And same-sex twins will share far more of their friends than opposite sex twins. Same-sex and monozygotic twins will also have more of the same friends because they’re very typically in the same social environment.

4 children playing blocks

So twins share friends, but is that a problem? We asked the children themselves. What we found was that identical, non-identical, same-sex, and opposite pairs were likely to say they enjoyed shared friendships. But some just responded, “Well, it’s my life.” They didn’t question it. Some said they hadn’t really thought about it. And a subset talked about absolutely not liking it.

Here are a few examples:

A. Identical twins: Typically enjoy or accept shared friends but there are exceptions
Researcher: “How do you feel about sharing your friends with your sister?”
Rebecca: “It is easy, it is not that bad because it means we can ummm … agree on people to invite around and things.” 
This is convenient for parents too.

Researcher: “How do you feel about sharing your friends with Lucy?”
Nicola: “I don’t really mind. I think it makes us have more friends each which is really better because we have each other’s friends as well as our own.”
Very nice.

Researcher: “How do you feel about sharing your friends with your twin?”
Lachlan: “Mmmm it’s like they’re candy and I have to give most of them to my brother … I usually spend all the hard work getting friends and Nicholas steals them off me.”
So Nicholas was less happy about being an identical twin who had to share his friends.
What we find with non-identical same-sex pairs, is there’s more conflict. They’re genetically less similar, but are placed together a lot. So what we see, again and again, is they like sharing friends, but only on certain conditions.

B. Non-identical twins: Typically enjoy or accept shared friends, but some specify circumstances of sharing

Researcher: “How do you feel about sharing your friends with Jane?”
Tammy: “I quite like it actually because like with Jane it’s lots of fun but without Jane it’s like we don’t have as much laughs.”

Researcher: “How do you feel about sharing your friends with Antonia?”
Shannon: “When they come around to play Antonia always wants to play with them as well but …”
Researcher: “And is that alright?”
Shannon: “Sometimes alright and other times it isn’t.”

We saw much more of these nuanced statements amongst non-identical twins, where shared friendships were conditional.

Starting school: To separate or not?

So what about going to school? When you’re a parent of twins, it’s not having twins that determines whether you should separate or bring children together. It’s about who those children are, who those individual children are, what their developmental strengths and problems are, and what their relationships are like. We’ve conducted large-scale Australian studies asking parents about their choices. And we’ve classified them by those who chose to keep children in the same class and those who chose to separate their children.

Not surprisingly, regardless of whether children are placed in the same class, or if they’re separated, parents talk about either decision as an advantage. The overwhelming difference is that parents – at entry to school – will only separate twins when there’s a problem, when there’s evidence of a risk for their twins specifically. For example, as children start school, parents make the case that their twins are already in a new situation, and the separation itself would be the stressor, so this risk meant twins were kept together. On the other hand, where poor behavior resulted from twins being together, or where one had a disability and the other one didn’t – parents make a decision to separate.

It was interesting that parents were very aware of the issues around individuality or keeping their children together – so they also voiced absence of risk: “Why would I separate them? We don’t have a problem. They’re fine together. Neither dominates. There’s not a problem, and it’s supportive to be together when you’re going through a transition.” Only a few families voicing an absence of risk separated their children – and that’s because the kids themselves decided that they’d quite like to try being in a different class.

FF jumping outside

What is important to remember is that parents don’t have to make a decision at the point of school-entry. Sometimes parents think it’s a ‘make-or-break’ decision that has to be made now.

However, many of the parents we studied had a transition plan. So that when their children went to school, they kept them together unless there was evidence of a problem. But they had a strategy: once they’d made their way through the transition to school, they would discuss separation with their children and they might make a decision to do so at another point. On the other hand, parents talked to us about having to bring children back together, after finding separation did not work. So it’s a process, and it’s a process of discussion with the children, families and the educators.

When we talked to teachers, they did not see many difficulties in having twin children together. But when they did talk about difficulties, it mostly wasn’t about being a twin. It was about general developmental difficulties. Teachers believed there were lots of strengths in being together in the transition to school, and only 23 percent of teachers described any difficulties in the twin children’s behaviour. So for three-quarters of the children studied, teachers had no comments to make on behaviour difficulties.

For some families there are quite big disparities or problems. They have to consider the needs of each individual child. We have a lot of data showing what parents consider in keeping children together or not: social support, anxiety, thinking about transition as a process, and the absence of something, not necessarily just the presence of a problem. And if you’re in this situation, speak to them. Five-year-olds are really good at telling us what they want.

So when you’re a parent of multiple-birth children, you have to consider whether there are problems to be concerned about – but don’t assume there are problems, because in the large majority of multiple birth children, particularly for children who’ve not experienced adversity in pregnancy or in the first postnatal year, they’re doing pretty well. Most twins develop normally. They’re only different to most children, because they have another child alongside them, and that’s it. A parent of twins has lots of challenges to monitor, but twins and multiples also bring incredible strengths and advantages in their relationship.

If you have any comments or questions, please This email address is being protected from spambots. You need JavaScript enabled to view

This blog is based on a presentation by Professor Thorpe to the Twin Community Forum held in Melbourne on 13 October 2017 by Twins Research Australia. The video of the presentation can be viewed below.

Twins Research Australia

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Twins Research Australia has received continuous funding from the National Health and Medical Research Council (NHMRC) since 1981, most recently through a Centre of Research Excellence Grant (2015-2022). TRA is administered by the University of Melbourne.

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