Comparison of Obstetric and Birthweight Characteristics Between the Two Largest Databases of Japanese Twins Measured in Childhood

Abstract

The purpose of this study is to compare obstetric and birthweight data of twin children from the two largest databases in Japan to estimate the difference between them in sample collection. The first group consisted of 1131 twin-pair school applicants, and the second group consisted of members' children from several maternal associations devoted to twins and included 951 pairs. All data were gathered by questionnaire. The mean birth years of the twins in these two databases were 1979 and 1995 respectively. The percentage of mothers treated with ovulation-stimulating drugs or in-vitro fertilization was markedly higher in the maternal associations group. Gestational age was around 1 week less in the maternal associations group, whereas birthweight according to gestational weeks and intrapair relative birth weight difference as a percentage according to zygosity showed little difference between both groups. We conclude that the obstetric and birthweight feature data from both groups should be considered to construct twin growth charts based on the methods of sample selection.

Triplets, birthweight, and handedness

“…adolescent twins (n > 2,000) reported a prevalence of 8.4% and 7.2% for left-handedness in boys and girls, respectively (23). In line with our study in triplets, sex differences in these samples including twins were evident only in the Netherlands (2), but not Japan (23).…”

Nongenetic factors associated with human handedness and footedness in Japanese twin children

“…None of the subjects in either group were severely retarded from the medical viewpoint with regards to physical growth and motor and language development at the time of data collection. The characteristics of both databases have been reported in detail elsewhere (9). The zygosity of the twins was determined primarily using a standard questionnaire (10), which was completed by the mothers.…”

“…The zygosity of the twins was determined primarily using a standard questionnaire (10), which was completed by the mothers. For the school applicant group, zygosity was also diagnosed using various DNA/genetic markers for those twin pairs who were actually admitted to the school, and this zygosity was obtained prior to that obtained using the questionnaire (9).…”

Twin Database of the Secondary School Attached to the Faculty of Education of the University of Tokyo

“…This selection bias would be fatal to some study designs. It has been found, however, that the birthweight according to gestational weeks was not different from that of the general twin population in Japan (Kato, 2004;Ooki & Asaka, 2005).…”

“…No subjects showed apparent growth retardation at 11 to 12 years of age. This dataset undoubtedly represents one of the largest and most thorough sets of accurate growth data on twins in Japan (Ooki & Asaka, 2005), especially since zygosity testing is very rare in Japan. The basic characteristics of the subjects in the applicants' database are presented in Table 1.…”