Studies of twins born 50+ years ago indicate that twins had a lower IQ than singletons. We carried out a register based study of all twins (N=3411) and a 5% random sample of singletons (N=7796) born in Denmark 1986-1988. We found no difference in school performance in adolescence between twins and singletons, nor when controlling for birth weight, gestational weight, age of parents or parents' education. Progress within living conditions, obstetrics, and paediatrics may be the reason why twins now generally have school performances similarly to singletons.
ReprintOf: BMJ. 2006 Nov 25;333(7578):109517012267