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Contributing factors

Between the age of 20 and 37-38, there is a consistent increase in a woman's chances of releasing more than one egg in each cycle and thus a greater chance of DZ twins or higher multiples. There is a separate increase associated with the number of children a woman has already had. Thus multiples are more likely to be born to older women and to be the later-born children in the family.

While there are some families with an extensive history of MZ or of both MZ and DZ multiples, most studies have focussed on a history of DZ tw MZ or of both MZ and DZ multiples, most studies have focussed on a history of DZ twins on the mother's side of the family. Evidence is less consistent for a role for males, either directly through a greater capacity for some men's sperm to fertilise two or more eggs or through a history of twinning in female relatives being passed on by men to their daughters. However it is fair to say the genetics of multiple birth are not clear because of two things:

(i) the mortality of multiples at birth is still higher than that of singletons but the survival rate is much better now than a generation or two ago.

"I said to my Mum that our boys would be the first twins in the family but she said that was not true. My aunt (Mum's sister) was the surviving member of a pair of twins, but it was something that has never been spoken about."

(ii) even if a family history of multiples does include those who died, as well as those who did survive, it is still not complete. Genetics is involved in the release of multiple eggs and not in whether these result in babies many months later. Ultrasound studies are showing that there are a considerable number of women who are carrying multiples 8-10 weeks into pregnancy at the time of a first scan. By the time of the next scan, there is a single fetus and so this is appropriately known as the "vanishing twin" syndrome. There may be no signs when the other multiple(s) are lost or at birth of the singleton and thus many people may be surviving multiples and not know it.

Assisted Reproduction

While much of the publicity surrounding higher multiple births in particular has focussed on in vitro fertilisation and its many developments, the majority of fertility treatments that result in multiples births are associated with the use of fertility drugs such as Clomid (Clomiphene). Many places are now setting strict guidelines on the number of fertilised eggs that can be implanted with in vitro fertilisation but it can be more difficult to control the number of eggs released by ovarian stimulation with drugs like Clomid.

It is really no business of the school to know whether a particular set of multiples resulted from assisted reproduction, except for two things:

(i) in an Australian study where we followed expectant couples from the time of diagnosis of twins, we found higher rates of stress and depression in those where there had been assisted reproduction, and this depression was present well before the birth. Obviously they were happy to finally be pregnant, but knowing some of the risks associated with multiples, especially in what could be their only chance at children was a heavy burden to bear. As discussed in the Preschool section anxiety and depression can limit the natural patterns of interaction that develop between parents and their newborn multiples.

(ii) every parent wants their child(ren) to succeed at school, but this may be especially so for parents who have used assisted reproduction. Not only may their multiples be their only children, they have spent much longer dreaming of how their children would develop and invested much time and effort in achieving this dream.