[Multiple births in The Netherlands, 1900-1988].

There are an estimated 120,000 twins and other multiples (all still alive) in The Netherlands. The age of this population (i.e. a quarter of a million persons, 1.6% of the total population) is slightly lower compared with The Netherlands as a whole. Alterations in the structure of mother's age and birth order can only partly explain the observed changes in multiple birth frequencies. The recent increase may be due to medical treatment of women with fertility problems. In addition dizygotic twin births appear to be largely responsible for the total development in multiple births. The changes in birth patterns which relate to the demographic variables age of mother and birth order, are hardly responsible for the decline of stillbirths, perinatal and infant mortality among twins and other multiples. This improvement can be ascribed mainly to progress in medical care. In spite of this improvement, the differences compared with singles are still considerable: the stillbirth rate for twins and other multiples is 2.5 times that for singles; the perinatal mortality rate and the infant mortality rate are about four times as high. However, in the first few years of life of twins and other multiples the age-specific mortality risk declines at such a rate that as early as the third year after birth there is hardly any difference with respect to the singles.