Higher Prevalence of Left-Handedness in Twins? Not After Controlling Birth Time Confounders.
Pregnancy- and birth-related factors may have an effect on handedness. Compared with singletons, twins have a lower birth weight, shorter gestational age, and are at higher risk for birth complications. We tested whether the prevalence of left-handedness is higher among twins than singletons, and if so, whether that difference is fully explained by pregnancy and birth-related differences between twins and singletons. We analyzed Finnish population-based datasets; included were 8,786 twins and 5,892 singletons with information on birth weight (n = 12,381), Apgar scores (n = 11,129), and gestational age (n = 11,811). Two twin cohorts were involved: FinnTwin12 included twins born during 1983-1987, and FinnTwin16 included twins born during 1974-1979. We had two comparison groups of singletons: 4,101 individuals born during 1986-1988 and enrolled in the Helsinki Ultrasound Trial, and 1,791 individuals who were partners of FinnTwin16 twins. We used logistic regression models with writing hand as the outcome for comparison and evaluating effects of covariates. Left-handedness was more common in twins (9.67%) than in singletons (8.27%; p = .004). However, Apgar scores were associated with handedness, and after controlling for covariates, we found no difference in the prevalence of left-handedness between twins and singletons. Increased left-handedness among twins, often reported by others, was evident in our data, but only among our older twin cohorts, and that association disappeared after removing effects of perinatal covariates.
Department of Public Health,University of Helsinki,Helsinki,Finland.
Kauko
K
Heikkilä
Department of Public Health,University of Helsinki,Helsinki,Finland.
Eero
E
Vuoksimaa
Department of Obstetrics and Gynecology,Helsinki University Hospital,Helsinki,Finland.
Aulikki
A
Saari-Kemppainen
Department of Public Health,University of Helsinki,Helsinki,Finland.
Jaakko
J
Kaprio
Department of Psychological & Brain Sciences,Indiana University,Bloomington,IN,USA.
Richard J
RJ
Rose
Department of Public Health,University of Helsinki,Helsinki,Finland.
Jari
J
Haukka
Department of Public Health,University of Helsinki,Helsinki,Finland.
Janne
J
Pitkäniemi
Department of Child Neurology,University of Helsinki,Helsinki,Finland.
Matti
M
Iivanainen
D000293:Adolescent; D000328:Adult; D001034:Apgar Score; D001724:Birth Weight; D005260:Female; D005387:Finland; D007839:Functional Laterality; D005865:Gestational Age; D006801:Humans; D008297:Male; D014427:Twins; D044465:White People; D055815:Young Adult
handedness; prenatal covariates; singletons; twins