Birth weight discordance of twin pairs and their subsequent growth patterns

Background: Few studies have compared the growth of a twin with its co-twin and particularly in relation to birth weight discordance. Aim: The study investigated how the degree of birth weight discordance affected subsequent growth. Methods: Birth weight discordance of 762 twin pairs was determined. Subsequent weight, height and occipital-frontal head circumference (OFC) measurements were obtained between the ages of 2-9 years. Corresponding standard deviations scores (SDS) were analysed according to birth weight discordance, sex and zygosity. Weight status was taken into account by assigning twins into sub-groups according to whether they were the heavier twin at birth and remained heavier, became the lighter of the twin pair or had the same weight, for subsequent measurements. Results and conclusions: The degree of birth weight discordance had little effect on subsequent growth except in monozygotic (MZ) twins with > 20% discordance. Severe low birth weight (< 1.95 kg) is more significant in suppressing subsequent growth than the degree of discordance per se. A surprisingly high proportion of twins reversed their weight status when reviewed at an older age.