On the standardisation of the twinning rate

Twin Research and Human Genetics, 2016

Strong geographical variations have been noted in the twinning rate (TWR). In general, the rate is high among people of African origin, intermediate among Europeans, and low among most Asiatic populations. In Europe, there tends to be a south–north cline, with a progressive increase in the TWR from south to north and a minimum around the Basque provinces. The highest TWRs in Europe have been found among the Nordic populations. Furthermore, within larger populations, small isolated subpopulations have been identified to have extreme, mainly high, TWRs. In the study of the temporal variation of the TWR in Norway, we consider the period from 1900 to 2014. The regional variation of the TWR in Norway is analyzed for the different counties for two periods, 1916–1926 and 1960–1988. Heterogeneity between the regional TWRs in Norway during 1916–1926 was found, but the goodness of fit for the alternative spatial models was only slight. The optimal regression model for the TWR in Norway has th...

Acta geneticae medicae et gemellologiae, 1995

Twin Research and Human Genetics, 2005

Twin research, 1999

There have been few secular analyses of the seasonal variation in human twinning and the results are conflicting. One reason for this is that the seasonal pattern of twinning varies in different populations and at different periods. Another reason is that the statistical methods used are different. The changing pattern of seasonal variation in twinning rates and total maternities in Denmark was traced for three periods (1855-69, 1870-94, and 1937-84). Two alternative methods of analysis are considered. The method of Walter and Elwood and a trigonometric regression model give closely similar results. The seasonal distribution of twin maternities for the periods in the 19th century showed highly significant departures. For both twin and general maternities, the main peaks can be seen from March to June and a local peak in September. During the springsummer season the twinning rates were higher than the total birth rates, indicating a stronger seasonal variation for the twin maternities than for the general maternities. For 1937-84, there was a similar, but less accentuated, pattern. Studies of other populations are compared with the Danish results. The more accentuated seasonal variation of twinning in the past indicate that some factors in the past affected women during summer-autumn and around Christmas time, making them more fecund and particularly to be more prone to polyovulation and/or more able to complete a gestation with multiple embryos.

Twin Research and Human Genetics, 2013

The French mathematician Bertillon reasoned that the number of dizygotic (DZ) pairs would equal twice the number of twin pairs of unlike sexes. The remaining twin pairs in a sample would presumably be monozygotic (MZ). Weinberg restated this idea and the calculation has come to be known as Weinberg's differential rule (WDR). The keystone of WDR is that DZ twin pairs should be equally likely to be of the same or the opposite sex. Although the probability of a male birth is greater than .5, the reliability of WDR's assumptions has never been conclusively verified or rejected. Let the probability for an opposite-sex (OS) twin maternity be p O , for a same-sex (SS) twin maternity p S and, consequently, the probability for other maternities 1 − p S − p O . The parameter estimatesp O andp S are relative frequencies. Applying WDR, the MZ rate is m = p S − p O and the DZ rate is d = 2 p O , but the estimatesm andd are not relative frequencies.

Twin Research and Human Genetics, 2019

Twinning is rare among humans, but there is much variability among populations. Several studies show that certain demographic and socioeconomic factors, such as maternal age, mother's educational level and income, influence twinning rate. There is no background of analytical studies of twins in Uruguay. To the best of our knowledge, this is the first study that has focused on describing and analyzing Uruguayan twinning rates over a period of 17 years (1999-2015). The birth data were collected from the website of Uruguay's Ministry of Public Health. Economic data were obtained from Uruguay's Instituto Nacional de Estadísti's website for the period 2001-2013, since these variables are defined specifically for that period of time. The statistical software R (The R Project for Statistical Computing) was used. The twinning rate varied from 8.51 to 13 in the studied period. Montevideo has the highest median and the smallest variability in comparison with the other departments. In Uruguay (1999-2015), the highest twinning rate (28.94%) was observed in women aged 45 and older. The analysis also showed a relationship between twin birth rates and the mother's educational level. In three regions of the country (West, Center and East), twin births show a random pattern but in the other two (North and Metropolitan), there is an increasing trend in the number of twins over time. In conclusion, this study recognizes social, economic and demographic factors that influence in the rate of twin births in Uruguay.

Human Reproduction, 2003

BACKGROUND: In the wide-ranging debate about the potential monitors of population fertility, twinning rate has been considered a candidate. In the developed countries, a decline in spontaneous twinning rate began around 1950 and continued until the late 1970s. The decrease in mean maternal age at delivery and the number of children per family have been considered as possible reasons for the decrease. The rise in twinning rates, which began in the 1980s, is probably due to the spread of assisted reproduction, at least for older mothers. METHODS: The temporal trend in twinning rate and the relationship with maternal age at delivery and birth order in the Italian population were analysed. RESULTS: The recent increase in twinning rate can be mainly attributed to the recourse to assisted reproduction techniques, as demonstrated by the twinning frequency among older primiparae. The twinning rate recently observed in young mothers approximates to the value of the 1950s, which is assumed to represent a`natural' fertility condition. CONCLUSIONS: On the assumption that twinning is an indicator of fertility, and hence of population ®tness, the present data seem to suggest that natural fertility has been slightly increasing in the Italian population.

Twin Research and Human Genetics, 2009

Dizygotic twinning rates have changed over time, which has been seen as a sign of a decline in fecundity. Since a woman's birthweight has been shown to be a marker of her fecundity, maternal birthweight may correlate with subsequent twinning rates. In the Danish National Birth Cohort (1996–2002), we examined if maternal birthweight, and whether she was born at term or preterm, correlated with her probability of multiple birth. For 20,719 live born infants, we had self-reported information about maternal birthweight, collected during the first wave of the 7-year follow-up, and information on multiple births from record linkage. The association between maternal birthweight and multiple births was investigated by use of logistic regression and presented as odds ratios (ORs) with 95% confidence intervals (CIs). Compared to women born at term with a birthweight of 3001–4000 g, women with a birthweight > 4500 g appeared to have higher chance of multiple birth while women with a bir...

Twin Research, 1998

The East Fl ander s Pr ospecti ve Tw i n Sur vey (EFPTS), star ted i n 1964, i s uni que among the 17 major Eur opean tw i n r egi ster s because i t i s popul ati on based, the tw i ns (and hi gher or der bi r ths) ar e ascer tai ned at bi r th, basi c per i natal data ar e col l ected, chor i on type i s establ i shed and, w hen appropriate, genetic markers including DNA fingerprints, are determined. The total number of sets i s 5089 tw i n, 158 tr i pl et and 14 of hi gher or der. Zygosi ty has been di agnosed on the basi s of sex, pl acental str uctur e and geneti c mar k er s i n mor e than 95% of pai r s. The EFPTS i s the onl y l ar ge r egi ster that i ncl udes pl acental data and al l ow s di ffer enti ati on of thr ee subtypes of monozygoti c tw i ns based on the ti me of the i ni ti al zygoti c di vi si on: the di chor i oni c-di amni oni c pai r s (ear l y), the monochor i oni c-di amni oni c pai r s (i nter medi ate), and the monochor i oni c-monoamni oni c pai r s (l ate). M ethodol ogy and basi c r esul ts i n tw i ns ar e consi der ed i n thi s ar ti cl e; detai l ed studi es will be r epor ted l ater. The sex pr opor ti on i n di zygoti c (DZ) tw i ns i s the same as i n si ngl etons, w her eas monozygotic (MZ) twins number more girls than boys. The difference in perinatal mortality between DZ and MZ twins is limited to the monochorionic MZ subgroup. Birth weight is highest in DZ twins and diminishes stepwise in MZ dichorionic and MZ monochorionic twins. Duration of pr egnancy fol l ow s the same tr end but i s l i mi ted to a few days. I atr ogeni c pr egnanci es ar e i ncr easi ng to the poi nt of r epr esenti ng al most 50% of the tw i n bi r ths i n 1997.

Acta geneticae medicae et gemellologiae, 1988

Twinning rates were studied in Swedes, Àland Islanders, Finns, Germana, and Dutch during years of starvation when death rates were two to three times higher than average. In contrast to the situation among some animals, this study suggests that nutrition above a certain threshold is unimportant for human reproduction, including twinning. The twinning rates for these different populations display marked temporal differences, but low values in the twinning rate are not consistently associated with periods of epidemics, famine, or similar nutritional stress. After years of privation and/or separation of spouses, a rapid "catch-up effect" can often be seen in the twinning rates, as well as marriage and birth rates. Psychoendocrine factors and interparental immunological conditions that may be involved in this phenomenon are discussed.