Growing up is double trouble for twins

Press, 18 June 1986, Page 19

Growing up is double trouble for twins

From

RHONDA DREDGE,

in Melbourne

Many identical twins are mirror images of each other. The facial structure, teeth, dominant hand, and even fingerprints of one are reversed in the other, Australian research has established. “One of our recent results is that the difference applies even at the level of the brain,” says an Australian psychologist, Dr David Hay, who leads one of the world’s largest studies of twin children, at La Trobe University, Melbourne. “The left half of the brain controls language skills in one twin while in the other it is the right half. These twins have different patterns of abilities which can be observed in language acquisition. One may have difficulty in the reception of language and the other in communication.” The La Trobe Twin Study has' grown to encompass about 1900 children, including 587 sets of twins and their siblings. As their physical and behavioural growth has been recorded over the last 10 years, the study has thrown new light on the multiple-birth family.

In the process Dr Hay and his researchers have helped hundreds of parents and their children to cope better with the experience. Dr Hay says there are two types of identical twins. Roughly one in three pairs results from the fertilised egg splitting three to four days after conception. They have separate placentas. The remainder split four to eight days after conception and share the same placenta. By the time the embryo divides into right and left half, it consists of quite a few cells. It is this group, says Dr Hay, that gives rise to “mirror image” twins in 70 per cent of these births and which is more prone to congenital abnormalities such as spina bifida and cleft palates. Another of the study’s major findings is the profound disadvantage twin boys face in gaining language-based skills at school. Dr Hay says that as many as 90 per cent at primary level had some reading problems while 23 per cent were seriously readingdisabled. Analysing data from an Aus-tralia-wide survey of children’s

competence in literacy and numeracy, Dr Hay confirms that twin boys lag behind in literacy skills even at the age of 14. Twin girls, however, are no different from non-twin girls. “Only 42 per cent of twin boys had reached mastery — the skills needed to cope in Australian society — compared with 71 per cent of single-born boys. Sadly, this situation appears to continue into higher education.” The delay in language acquisition among twins is well documented. They are older when they say their first word, their sentences are shorter, and baby talk persists longer. The study has, however, thrown some light on the socalled "secret language” of twins. While most twins have some special made-up words, Dr Hay says their language is usually the result of omitted letters and syllables as they try to get their message across before the other twin interrupts.

“In this sense their language is very adaptive to their own environment but unfortunately maladaptive to other situations. Until recently it was believed the language problems gradually diminished until around the time of starting school twins were no different from single-born children. But it now appears that shaky foundation has to be corrected early.” Dr Hay advises parents to send their twins on alternate days to pre-school centres where forced contact with other children will accelerate language development. The twin at home'will then benefit from the individual attention of the parent who has generally been too busy attending to the basic needs of two. Identical twins have been found to be the group most at risk for a range of social and learning problems. Even the events at birth can set the scene for how they are treated during the rest of their childhood.

“We find that parents often feel closer to the first-born, who is easier to manage and healthier as a baby,” Dr Hay says. “The fact that this first-born difference is reported more often for identical twins suggests that parents have a definite need to distinguish between them. “The difference continues well into primary school, where the first-born child is seen as more dominant, independent, and better co-ordinated. Surprisingly, teachers confirm these observations without knowing the birth order of the twins. Parents should be aware of the way they can stereotype their children.” One puzzling side of the twin story is the finding that the proportion of twins who are identical is rising in some countries. In 1955, less than 30 per cent of the twins born in Australia were identical. Now it is closer to 50 per cent. Dr Hay attributes the proportional increase to more adequate contraception. “Fraternal twins are more often born to older mothers. Oral contraceptives mean that these women can more successfully plan their

families. Dr Hay says that in the past few years scientists had changed their thinking about who had twins and why. One of the most startling results has come from ultrasound studies which show that two out of every three pregnancies diagnosed as twins at eight weeks are single pregnancies by 16 weeks. This means that one in every 33 births may start out as twins. These “vanishing twins,” normally reabsorbed or expelled when the other twin is bom, challenge ideas about the role of family history in twinning. Dr Hay, recently back from a three-month stint in Antarctica, says the study of twins has taken him in many unforeseen directions. His search in Antarctica for an unusual freshwater worm is one of the strangest The worm is able to regenerate itself from the left or right side of its body when cut in half. “It is potentially a very good model for the development of 'mirror image’ twins,” Dr Hay adds. Copyright—Australian Information Service.