The cognitive cost of being a twin: evidence from comparisons within families in the Aberdeen children of the 1950s cohort study

Georgina A Ronalds; Bianca L De Stavola; David A Leon

doi:10.1136/bmj.38633.594387.3A

The cognitive cost of being a twin: evidence from comparisons within families in the Aberdeen children of the 1950s cohort study

Georgina A Ronalds
, Bianca L De Stavola
, David A Leon

Aberdeen Children of the 1950s

Research output: Contribution to journal › Article › peer-review

75 Citations (Scopus)

Abstract

OBJECTIVES: To determine whether twins have lower IQ scores in childhood than singletons in the same family and, if so, whether differences in fetal growth explain this deficit.

DESIGN: Cohort study.

SETTING: Scotland.

PARTICIPANTS: 9832 singletons and 236 twins born in Aberdeen between 1950 and 1956.

RESULTS: At age 7, the mean IQ score of twins was 5.3 points lower (95% confidence interval 1.5 to 9.1) and at age 9, 6.0 points lower (1.7 to 10.2) than that of singletons in the same family. Adjustment for sex, mother's age, and number of older siblings had little effect on these differences. Further adjustment for birth weight and gestational age attenuated the IQ difference between twins and singletons: the difference in mean IQ was 2.6 points (-1.5 to 6.7) at age 7 and 4.1 points (-0.5 to 8.8) at age 9.

CONCLUSIONS: Twins have substantially lower IQ in childhood than singletons in the same family. This effect cannot be explained by confounding due to socioeconomic, maternal, or other family characteristics, or by recruitment bias. The reduced prenatal growth and shorter gestations of twins may explain an important part of their lower IQ in childhood.

Original language	English
Article number	1306
Number of pages	5
Journal	BMJ (Clinical research ed.)
Volume	331
Issue number	7528
DOIs	https://doi.org/10.1136/bmj.38633.594387.3A
Publication status	Published - 3 Dec 2005

Funding

The Aberdeen children of the 1950s study was funded as a component project (G0828205) of a Medical Research Council Co-operative Group on Life-course and trans-generational influences on disease risk (G9819083) GAR was funded by grant from the Scottish Chief Scientist Office.

Keywords

Adolescent
Adult
Aged
Birth Weight
Child
Cognition Disorders/psychology
Cohort Studies
Educational Status
Family Characteristics
Female
Fetal Growth Retardation/psychology
Humans
Intelligence
Male
Middle Aged
Regression Analysis
Scotland
Twins/psychology

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10.1136/bmj.38633.594387.3A

Cite this

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title = "The cognitive cost of being a twin: evidence from comparisons within families in the Aberdeen children of the 1950s cohort study",

abstract = "OBJECTIVES: To determine whether twins have lower IQ scores in childhood than singletons in the same family and, if so, whether differences in fetal growth explain this deficit.DESIGN: Cohort study.SETTING: Scotland.PARTICIPANTS: 9832 singletons and 236 twins born in Aberdeen between 1950 and 1956.RESULTS: At age 7, the mean IQ score of twins was 5.3 points lower (95\% confidence interval 1.5 to 9.1) and at age 9, 6.0 points lower (1.7 to 10.2) than that of singletons in the same family. Adjustment for sex, mother's age, and number of older siblings had little effect on these differences. Further adjustment for birth weight and gestational age attenuated the IQ difference between twins and singletons: the difference in mean IQ was 2.6 points (-1.5 to 6.7) at age 7 and 4.1 points (-0.5 to 8.8) at age 9.CONCLUSIONS: Twins have substantially lower IQ in childhood than singletons in the same family. This effect cannot be explained by confounding due to socioeconomic, maternal, or other family characteristics, or by recruitment bias. The reduced prenatal growth and shorter gestations of twins may explain an important part of their lower IQ in childhood.",

keywords = "Adolescent, Adult, Aged, Birth Weight, Child, Cognition Disorders/psychology, Cohort Studies, Educational Status, Family Characteristics, Female, Fetal Growth Retardation/psychology, Humans, Intelligence, Male, Middle Aged, Regression Analysis, Scotland, Twins/psychology",

author = "Ronalds, \{Georgina A\} and \{De Stavola\}, \{Bianca L\} and Leon, \{David A\}",

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doi = "10.1136/bmj.38633.594387.3A",

language = "English",

volume = "331",

journal = "BMJ (Clinical research ed.)",

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number = "7528",

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T2 - evidence from comparisons within families in the Aberdeen children of the 1950s cohort study

AU - Ronalds, Georgina A

AU - De Stavola, Bianca L

AU - Leon, David A

PY - 2005/12/3

Y1 - 2005/12/3

N2 - OBJECTIVES: To determine whether twins have lower IQ scores in childhood than singletons in the same family and, if so, whether differences in fetal growth explain this deficit.DESIGN: Cohort study.SETTING: Scotland.PARTICIPANTS: 9832 singletons and 236 twins born in Aberdeen between 1950 and 1956.RESULTS: At age 7, the mean IQ score of twins was 5.3 points lower (95% confidence interval 1.5 to 9.1) and at age 9, 6.0 points lower (1.7 to 10.2) than that of singletons in the same family. Adjustment for sex, mother's age, and number of older siblings had little effect on these differences. Further adjustment for birth weight and gestational age attenuated the IQ difference between twins and singletons: the difference in mean IQ was 2.6 points (-1.5 to 6.7) at age 7 and 4.1 points (-0.5 to 8.8) at age 9.CONCLUSIONS: Twins have substantially lower IQ in childhood than singletons in the same family. This effect cannot be explained by confounding due to socioeconomic, maternal, or other family characteristics, or by recruitment bias. The reduced prenatal growth and shorter gestations of twins may explain an important part of their lower IQ in childhood.

AB - OBJECTIVES: To determine whether twins have lower IQ scores in childhood than singletons in the same family and, if so, whether differences in fetal growth explain this deficit.DESIGN: Cohort study.SETTING: Scotland.PARTICIPANTS: 9832 singletons and 236 twins born in Aberdeen between 1950 and 1956.RESULTS: At age 7, the mean IQ score of twins was 5.3 points lower (95% confidence interval 1.5 to 9.1) and at age 9, 6.0 points lower (1.7 to 10.2) than that of singletons in the same family. Adjustment for sex, mother's age, and number of older siblings had little effect on these differences. Further adjustment for birth weight and gestational age attenuated the IQ difference between twins and singletons: the difference in mean IQ was 2.6 points (-1.5 to 6.7) at age 7 and 4.1 points (-0.5 to 8.8) at age 9.CONCLUSIONS: Twins have substantially lower IQ in childhood than singletons in the same family. This effect cannot be explained by confounding due to socioeconomic, maternal, or other family characteristics, or by recruitment bias. The reduced prenatal growth and shorter gestations of twins may explain an important part of their lower IQ in childhood.

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KW - Cognition Disorders/psychology

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KW - Educational Status

KW - Family Characteristics

KW - Female

KW - Fetal Growth Retardation/psychology

KW - Humans

KW - Intelligence

KW - Male

KW - Middle Aged

KW - Regression Analysis

KW - Scotland

KW - Twins/psychology

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JO - BMJ (Clinical research ed.)

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M1 - 1306

ER -

The cognitive cost of being a twin: evidence from comparisons within families in the Aberdeen children of the 1950s cohort study

Abstract

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Keywords

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