A comparison of growth in twins and singleton controls of matched age followed longitudinally from 10 to 18 years.

A sample of 323 pairs of twins (94 MZ pairs, 133 DZ like-sexed pairs and 97 DZ unlike-sexed pairs born in 1954/55) were studied longitudinally from 10 to 18 years for boys and 10 to 16 years for girls. Height, weight, age at menarche and peak height and weight velocities (PHV and PWV) were studied. No significant differences occurred between twin categories in any two of these varieties, so in each sex the total twin group was compared with a group of matched singleton controls (380 boys and 360 girls). There were very small differences between the twin boys and their controls in height, weight and PWV-age. PHV occurred somewhat earlier in twin boys than in the controls. The height and weight peaks were significantly lower for the twin boys. For twin girls, however, a height and weight deficit was found during puberty and they also matured a little later than their controls according to both PHV, PWV and menarche. The height and weight peaks were also somewhat lower for the twin girls. One reason for the observed sex differences could be a proportionally higher mortality for twin boys, thus an effect of selective survival.