The growth, development and education of Finnish twins: a longitudinal follow-up study in a birth cohort from pregnancy to nineteen years of age

The growth, development and vocation of 289 twins in a one year birth cohort beginning during pregnancy and followed up to the age of 19 years was compared with that of 11,623 singletons and two sets of controls matched either by maternal factors only or by these and perinatal morbidity, all from the same cohort. The twins were more often pre-term and small for their gestational age, and had more often suffered from perinatal asphyxia, neonatal hyperbilirubinaemia and hypoglycemia. They had learned to walk without support later than the singletons and the controls matched only by maternal factors, but this difference did not exist between the twins and the controls also matched by perinatal morbidity. The same kind of result was found when studying the number of words spoken at the age of one year and physical growth at the ages of 1 and 14 years. The twins did not differ significantly from the singletons during their compulsory nine years of primary and secondary schooling. According to the national registers of vocational choices, the twins had applied for admission to further education courses less often than the singletons or their controls matched only by maternal factors, but not when compared with the controls also matched by perinatal morbidity. Logistic regression analysis revealed numerous perinatal or environmental factors having an adverse effect on educational achievements, but the twin situation itself was not shown to have adverse effects. About half of the same-sex twin pairs and one seventh of the opposite-sex pairs had chosen the same vocation, compared with just over 10% similarity between the twins and their controls.