For more than 80 years, we’ve known that – on average – twins develop language more slowly than single children (e.g. Day, 1932).
More recent studies have shown that:
- twins – particularly boys – have a higher risk of developmental language disorders than single children (e.g. Hay et al., 1987, Rutter et al., 2003); and
- except in the case of twins born before 33 weeks and/or with obvious brain damage, twins’ language disorders are typically mild, and sometimes resolve by middle childhood (e.g. Thorpe et al., 2001).
Why are twins at risk?
Over the years, researchers have put forward different ideas:
- twinning is associated with a higher rate of prematurity and obstetric complications, which are both in themselves risk factors for language disorders (e.g. MacGillivray et al., 1988, Falkner & Matheny, 1995);
- “Twin-twin transfusion syndrome”: twins who share a placenta pre-birth may experience inter-twin transfusion, which results in one twin having a blood over-supply, and the other an under-supply, which in turn affects birth weight and postnatal development (e.g. Cincotta, 2000, but see Rutter et al., 2003);
- “Twin language”: some twins develop their own private language, which may impede normal language development (Bakker, 1987, Bishop & Bishop, 1998, see below);
- social environmental risk: On average, twin children:
- experience less individually focused interaction with their mothers and fathers than single children (Lytton et al., 1987; Tomasello et al., 1986); and
- spend more time with a sibling of the same developmental level (Koeppen-Schmerus et al., 1986).
Many of the studies cited above are small case studies. The weight of more recent evidence suggests that mild language delays evident in twin children:
- are not attributable to obstetric or pre-birth effects (apart from twins born before 33 weeks and/or with overt brain damage); and
- are largely explained by social experiences in the early social environment of twins (Thorpe, 2006).
Why might parent interaction with twins be of lower quality than interaction with a single child?
We don’t know for sure.
- Parents might think twins are “company for each other” and therefore less in need of interaction with their parents.
- Logistical difficulties: parents don’t have as much time for each child when they have to look after twins (not to mention any siblings!).
- Emotional stressors: understandably, parents of twins are more susceptible to clinical and sub-clinical levels of depression, which can reduce their interaction with their children and responsiveness.
- A combination of the above.
Do twins develop their own language?
Lots of people – including many parents of twins – think that twins develop their own separate and exclusive communication system. In one older study, almost 50% of parents reported that their twins shared a “twin language” (Mittler, 1970). “Twin language” is thought by some researchers to get in the way of normal language development and to thus contribute to the heightened risk of language delay.
Two main types of twin-language have been studied:
- Shared understanding: Many instances of twin language occur because twins share so much of their lives together and are better able to understand each other’s immature speech. They have a shared understanding gained from spending so much time doing things together. This shared understanding is thought to be very common: around 50% of twins at 20 months and around 20% at 3 years; and
- Private language: True “twin-speak” – a completely private language used just by the twins to speak with each other – is rarer. At 20 months, around 11.8% of twins use a private language, and this falls to around 6.3% at 3 years of age. Private language is associated with an unusually close relationship and poorer overall cognitive functioning. It occurs mainly with male and monozygotic (identical twin) children. Longer term language outcomes are poorer for this group than twins with shared understanding (Thorpe et al., 2001).
Even without intervention, both types of twin-language decline over time and seem to disappear by middle childhood. It’s worth noting that shared understanding and private language are not exclusive to twins. They can also happen with close siblings of different ages, although this is less common.
How can we help twins with their language development?
If we accept that twins are more vulnerable to language disorders because of their social environments, two broad strategies can help:
- Improving the language environment within the family: Specifically:
- increasing the one-to-one interaction between each twin and his/her parents;
- learning language stimulation strategies to improve the quality and quantity of interaction between each twin and his/her parents;
- dividing care for each twin between parents at different times so that each twin gets more one-on-one interaction with a parent;
- enlisting grandparents, relatives and friends to support parents with household tasks to free up more time for parents to interact with each twin; and
- seeking guidance from twin support groups and twin clubs;
- Improving the quality of the language environment through out-of-home support:
- pre-school education can give twins an opportunity for separation prior to school entry and open up a wider social experience – although there is some evidence this is of limited benefit if the twins stick together and don’t look outside each other for friendships and/or are too delayed in their development to interact effectively with peers (e.g. Hay et al., 1987, Hay et al., 1990); and
- increased socialisation with others through play dates, trips to the library, and participation in playgroups, craft groups, sporting teams, etc.
Clinical bottom line
Compared to single children, twins are at a higher risk for developmental language disorders – especially if they develop their own private language. Often, language delays in twins result from environmental and social factors. Treatment should therefore focus on improving language experiences for each twin in and out of the home. One-to-one parent interaction with each twin is important. In some cases, separation of the twins (e.g. into separate sporting teams or pre-school or school classes) might help improve engagement, interaction with others and thus language development.
Principal source: Thorpe, K. (2006). Twin children’s language development. Early Human Development, 82, 387-395.
Hi there, I’m David Kinnane.
Principal Speech Pathologist, Banter Speech & Language
Our talented team of certified practising speech pathologists provide unhurried, personalised and evidence-based speech pathology care to children and adults in the Inner West of Sydney and beyond, both in our clinic and via telehealth.