Letters to the Editor

Abstract

We appreciate Dr. Pick's interest in our paper on dissimilar sized twins. It may be as Dr. Pick suggests that some infants of small birth weight for their gestational age grow and develop "normally." Our study has demonstrated the failure of the undersized member of twin pairs to achieve a comparable level of growth and development to that of the co-twin at the time of the study examination. The reasons for this continued disproportion in size are not clear. Further studies are necessary to relate all possible factors concerned in intrauterine growth retardation with the subsequent development of the child.

Birthweight Differences, The Transfusion Syndrome and The Cognitive Development of Monozygotic Twins

“…Some of these are: a) MZ twins with a PDB > 25% and below 2,000 g form a unique group probably affected by the TTS. The heavier twins in this group scored significantly better on the Stanford Binet and PPVT test [3]. b) The heavier twins scored better only on the Performance Scale of the WISC [15].…”

“…Despite a "plea" to the obstetrician by Benirschke [6] and others [20,44] during the 1960s, that such accurate placental data be recorded at birth, the practice is stili not widespread and may be the main reason why most studies of twins either fail to recognize these potentially important differences in the prenatal environment or do not have the necessary placental data to take them into account [8,16]. Even in the 1950s Price [39] warned that interpretations of twin differences are not valid unless intrauterine variations have been considered and others since have reemphasized their warning [3,16,5]. As well as the obvious implications for genetic analysis using twins, intrauterine differences could well be criticai to the long-term cognitive development of twin children.…”

“…However, only very few studies on longer term effects have been conducted, most studies are not recent and they present significant methodological deficiencies. The possible relationship of these weight differences to the transfusion syndrome is rarely explicitly stated and is stili poorly understood by some researchers [3,4]. Even fewer studies have examined the effects of the severity of the syndrome, as indicated by magnitude of weight difference.…”

“…In 1964 the performance of 16 sets of "like sex" twins from 4.5 to 11 yearsof age, where the lighter twin was at least 25% smaller and weighed less than 2,000 g at birth, was examined on the Stanford-Binet IQ test, the Peabody Picture Vocabulary test (PPVT) as well as on speech development and physical growth measures [3]. For the 9 MZ sets (as determined by bloodtyping and physical appearance), they found a significant difference of 6.6 Binet IQ points and 2.7 PPVT IQ points in favour of the heavier twin.…”

“…Kamin, correcting errors, found there was an IQ advantage to the heavier twin of around 5 IQ points which was independent of difference or similarity in BW. However, he falsely equates both Babson's [3] 25% weight difference category and Fujikura and Froelich's [24] 15% PDB group with his 300 g group, and his pooled data stili suffers from the invalidities of different samples and IQ tests. He also denies that the effect found can be attributed to the TTS.…”