Twins: Two by two

You can respect twin children's characteristics while treating the two of them as unique individuals. Dr Penny Munn gives advice for sensitive double dealing

There are two different kinds of twins. Non-identical, or fraternal, twins result from a double fertilisation; identical twins result from an embryo splitting after conception. Non-identical twins are no more alike than ordinary siblings; identical twins are completely alike, genetically speaking. Most twins are non-identical.

Since 1980, the number of twin births has been steadily rising in the developed world. In the UK, the incidence was ten in every thousand births in that year whereas it is now around 14 in every thousand births. But this increase has been in non-identical twins. Identical twins are much more rare, at four per thousand births and are no more frequent now than they ever were. They are chance events and are not affected by any of the factors associated with fraternal twin births, such as infertility treatments or delayed motherhood (hormone changes in older women increase the likelihood of fraternal twins). Sometimes twin children can cause a fair amount of trouble for their families. On average, pregnancy and birth are more difficult, and birth weight and survival rates are lower. Rates of disability of all kinds are higher because of birth and pregnancy problems. Twins are also more difficult and expensive to rear, so there are both problems and delights for parents with the double pregnancy.