Alternate Changes in Birth Seasonality of Twins During 1971–1984 in Japan

Nakamura, Izumi; Amau, Y.; Nonaka, Kazuhiro; Miura, Teiji

doi:10.1017/s0001566000006139

Cited by 7 publications

(6 citation statements)

References 17 publications

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“…However, when observed each year, this seasonality was not always found, there being some exceptional years such as 1979, 1980, and 1993. This instability may be consistent with the intermittent appearance of seasonality in twinning reported by Nakamura et al (1987). The present results suggest that there is a basic tendency for multiple ovulation to occur more in October-March, which roughly corresponds to births in July-December.…”

Section: Discussionsupporting

confidence: 89%

“…Imaizumi et al (1980) reported seasonality in the twinning rate in Japan in 1974 through a nationwide survey, noting that there was an elevation in April for both MZ and DZ twin births. Nakamura et al (1987) analyzed data from a Japanese association for the mothers of twins, and found evidence suggesting variation in the seasonality of twinning: no apparent seasonality in some consecutive years and elevation in summerto-fall months in other consecutive years.…”

Section: Discussionmentioning

confidence: 99%

“…In Japan, there have been several reports on this subject (Imaizumi et al 1980;Kamimura 1976;Nakamura et al 1987), but so far the data used have been either for a single year (Imaizumi et al 1980), or only for a limited area (Kamimura 1976), or dependent on a small sample size (Nakamura et al 1987).…”

Section: Introductionmentioning

confidence: 99%

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Monthly trend and seasonal variation in twinning rate in Japan, 1975-1994

Nonaka¹,

Imaizumi

1999

International Journal of Biometeorology

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We examined birth records from Japanese statistics, 1975-1994, to investigate the seasonality of twin births. We could identify 198,924 pairs of twins (97.9% of all the registered twin records) and estimated the numbers of mono- and dizygotic twin pairs. The seasonal index of the twinning rate for each month was calculated by dividing the crude rate by the estimated trend value for the month. There were significant variations in the seasonal index for overall, dizygotic and monozygotic twinning rates. Peak months with values more than 3% higher than expected were July and October-December for dizygotic twins, and April and June for monozygotic twins; these seasonalities were statistically significant by analysis of variance and the patterns were similar in recent years, with a sharp increase in the total twinning rate. When observed year-by-year, however, there were years that did not show these typical seasonalities. It is suggested that the mechanisms for probable seasonal variations in twinning rates are different for dizygotic and monozygotic twin pregnancies, and that factors involved in these variations are not effective every year.

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Section: Discussionsupporting

confidence: 89%

Section: Discussionmentioning

confidence: 99%

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Monthly trend and seasonal variation in twinning rate in Japan, 1975-1994

Nonaka¹,

Imaizumi

1999

International Journal of Biometeorology

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“…Table 2 -Association (OR) of concordant-sex, discordant-sex, and all twin birth events with conception during March-August, by type of analysis Analysis Crude analysis 1 Matched analysis 2 Logistic regression (unconditional) 13 Logistic regression (conditional) [2][3] All n = 2336 OR (95% C.I. )…”

Section: Resultsmentioning

confidence: 99%

“…Although there exists strong support for an inherited susceptibility to twinning [4,14], there are reasons to believe that environmental factors play a role as well. Among the latter are several studies demonstrating cyclic variations in twin births within geographi-cally defined populations [6][7][8]13,[15][16][17]. One interpretation of such patterns is that they reflect changes in ambient luminosity and subsequent promotion of multiple ovulations in women who are genetically predisposed to twinning [1,2,9,12].…”

Section: Introductionmentioning

confidence: 99%

Seasonal Variation of Twin Births in Washington State

Dionne

Söderström

1993

Acta genet. med. gemellol.: twin res.

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Twin births are known to vary across seasons in several countries. It has been hypothesized that this variation may be due to seasonal changes in luminosity leading to pineal gland-mediated multiovulation among susceptible mothers. To describe seasonal variation of twin births in Washington State, all mothers residing in Washington State who gave birth to both a pair of twins and a singleton baby between 1984-1990 (n = 1168) were identified through linkage of computerized State birth certificates. Using a “matched-on-mother” case-control design, the estimated month of conception of twin gestations (the “case” events) were compared to that for their singleton siblings (the “control” events) to determine their relative occurrence during periods of high vs low sunlight in accordance with local climatological data. For the study population as a whole, there was only a slight tendency for twins to have been conceived during the period of high sunlight compared to their singleton siblings (OR = 1.3, 95% C.I. = 1.0-1.7). When stratified by concordant-sex vs discordant-sex, however, more discordant-sex twin pairs were conceived during the light period than corresponding singletons (OR = 1.7, 95% C.I. = 1.0-2.8), whereas no association was found for concordant-sex twins (OR =1.1, 95% C.I. =0.8-1.6). The presence of an association only among discordant-sex twins, all of whom are dizygotic, is consistent with the hypothesis that exposure to sunlight may stimulate multiple ovulation, and thus increase the incidence of twin gestations among twin-prone mothers.

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Low twinning rate and seasonal effects on twinning in a fertile population, the Hutterites

1993

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This paper analyzes from the mid 18th century to 1987 the birth records of the "Dariusleut," one of the three subgroups of the Hutterite population. The aim of this study is to describe several aspects of the twinning rate in a fertile population. The overall rate of twinning was 0.90%: 103 twins among all 11,492 maternities. The rate peaked at the 7th birth order and at the maternal age of 40 years and over. Until the mid 19th century when the Hutterites lived in Russia, the twinning rate was higher (1.5%), and it decreased during the migration period in the second half of the 19th century (0.7%). After the group had settled in the USA and Canada, the population maintained a twinning rate of 1.0% until 1965. After 1965 the rate decreased to 0.7%, partly due to a decline in fertility among women aged 30 years and over. There was a significant seasonal variation: the twinning rate decreased to 0.5% in May-July compared to 1.2% for the other three seasons during the years up to 1965 (P < 0.01), while more recent mothers did not show such a seasonal variation. The incidence of twin births in this population seems to have been influenced by environmental factors, which would change their effect seasonally and secularly.

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Alternate Changes in Birth Seasonality of Twins During 1971–1984 in Japan

Cited by 7 publications

References 17 publications

Monthly trend and seasonal variation in twinning rate in Japan, 1975-1994

Monthly trend and seasonal variation in twinning rate in Japan, 1975-1994

Seasonal Variation of Twin Births in Washington State

Low twinning rate and seasonal effects on twinning in a fertile population, the Hutterites

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