Multiple births from medically assisted reproduction: contribution of different types of procedures and trends over time.

OBJECTIVE: To evaluate the relative impact of different strategies of medically assisted reproduction (MAR), i.e. first line treatment (ovarian stimulation with or without intrauterine insemination) and in vitro fertilization (IVF) procedures (conventional IVF or intracytoplasmic sperm injection), on the risk of multiple births. STUDY DESIGN: We utilized the health care utilization databases of the Lombardy region to identify births resulting from MAR between 2007 and 2022. We gathered data on the total number of multiple births and calculated the prevalence rate by dividing the number of multiples by the total number of births. To examine the temporal trend in the proportion of multiple births after MAR over time, a linear regression model was employed separately for different types of techniques and in strata of maternal age. RESULTS: A total of 30,900 births after MAR were included; 4485 (14.5 %) first line treatments and 26,415 (85.5 %) IVF techniques. Overall, 4823 (15.6 %) multiple births were identified. The frequency of multiple births over the study period decreased from 22.0 % in 2007 to 8.7 % in 2022 (p < 0.01). Multiple births from first line treatments were stable ranging from 13.5 % in 2007-2008 to 12.0 % in 2021-2022 (p = 0.29). Multiple births from IVF procedures decreased from 23.8 % in 2007-2008 to 8.4 % in 2021-2022 (p < 0.01). Stratifying for maternal age (i.e. < 35 and ≥ 35 years), the trends remained consistent. CONCLUSIONS: The reduction in multiple births has been influenced by changes in IVF strategy and procedures. The decline has been gradual but steady since 2009, when a law restricting embryo freezing was repealed in Italy. In contrast, the proportion of multiple births resulting from first line treatments has remained constant over time. Despite declining, multiple births from MAR remained about one order of magnitude higher than those from spontaneous pregnancies.

Assisted Reproductive Technology, Multiple Births, and Perinatal Outcomes in Taiwan from 2001 to 2020.

OBJECTIVE: To investigate the effect of the Assisted Reproduction Act, implemented in 2007 in Taiwan to reduce the number of embryos to transfer, on the trends over time regarding the rate of multiple births, preterm delivery, low birth weight (LBW), and small for gestational age (SGA) among deliveries using assisted reproductive technology (ART). STUDY DESIGN: From the Birth Reporting Registry and the Assisted Reproduction Registry, we retrieved data of 4 016 530 live birth deliveries between 2001 and 2020; among them 71 000 (1.77%) were after ART. We calculated the rate of multiples and perinatal outcomes per 1000 deliveries annually from 2001 to 2020 for deliveries using and not using ART and computed the population attributable risk. We performed interrupted time series to assess the effect of the intervention, ie, the Assisted Reproduction Act. RESULTS: The proportion of deliveries following ART was 0.57% in 2001 and increased to 4.03% in 2020. After the intervention, there were decreasing trends over time for rates of multiples (-10.63 per year, P < .001), preterm delivery (-6.74, P = .003), LBW (-9.38, P < .001), and SGA (-4.48, P = .001) among ART deliveries. There was also an immediate decrease right after intervention (-53.45, P = .005) for SGA after ART. The population attributable risk trends before and after intervention were both increasing for all outcomes. CONCLUSIONS: The Assisted Reproduction Act in Taiwan was associated with a decreasing trend of multiples, preterm delivery, LBW, and SGA over time since 2008 among ART deliveries. In particular, there was an immediate decrease of SGA right after the intervention.

Celebrating 30 years of ART in Latin America; and the 2018 report.

RESEARCH QUESTION: What are the trends in patient characteristics, effectiveness and safety of assisted reproductive technology (ART) performed in Latin America over the past three decades, as well as the detailed outcomes of procedures initiated in 2018? DESIGN: Retrospective collection of multinational data including epidemiology and outcomes of ART performed between 1990 and 2018. RESULTS: Over these 30 years we report 955,117 initiated cycles, 191,191 deliveries and 238,045 live births. In 1990, 66.5% of women were ≤34 years and 8.7% ≥40 years; in 2018, 26.4% of women were ≤34 years and 32.0% were ≥40 years. In 1990, 60.4% of transfers included ≥3 embryos, falling to 13.5% in 2018, and single embryo transfer (SET) increased from 13.8% to 30.4% between 1990 and 2018. Delivery rate per fresh transfer increased from approximately 17% in the 1990s to 25% in 2018, with a meaningful drop in high-order multiples, from 5-9% in the 1990s to 0.4% in 2018. This drop is associated with increasing use of frozen embryo transfer (FET) (57% in 2018) compared with 10% in 2000. In 2018, delivery rate in FET was 28.3%, reaching 31.2% in freeze-all cycles; and the cumulative live birth rate (fresh + FET) was 41.9%. Elective SET also increased, from 0.9% in 2010 to 10% in 2018. The delivery rate in elective SET (31.7%) was only 5.4% lower than elective double embryo transfer (DET) (37.1%); however, multiple births increased from 2.1% to 25.5% twins and 0.4% triplets in elective DET. CONCLUSION: The Latin American Registry of Assisted Reproduction (RLA) celebrates 30 years of voluntary reporting from a total of nearly 200 centres in 15 countries. This South-South Cooperation network has proven to be an efficient and safe system for technological transfer and regional growth.

Births: Final Data for 2019.

Objectives-This report presents 2019 data on U.S. births according to a wide variety of characteristics. Trends in fertility patterns and maternal and infant characteristics are described and interpreted. Methods-Descriptive tabulations of data reported on the birth certificates of the 3.75 million births that occurred in 2019 are presented. Data are presented for maternal age, livebirth order, race and Hispanic origin, marital status, tobacco use, prenatal care, source of payment for the delivery, method of delivery, gestational age, birthweight, and plurality. Selected data by mother's state of residence and birth rates by age are also shown. Trend data for 2010 through 2019 are presented for selected items. Trend data by race and Hispanic origin are shown for 2016-2019. Results-A total of 3,747,540 births were registered in the United States in 2019, down 1% from 2018. The general fertility rate declined from 2018 to 58.3 births per 1,000 women aged 15-44 in 2019. The birth rate for females aged 15-19 fell 4% between 2018 and 2019. Birth rates declined for women aged 20-34 and increased for women aged 35-44 for 2018-2019. The total fertility rate declined to 1,706.0 births per 1,000 women in 2019. Birth rates declined for both married and unmarried women from 2018 to 2019. The percentage of women who began prenatal care in the first trimester of pregnancy rose to 77.6% in 2019; the percentage of all women who smoked during pregnancy declined to 6.0%. The cesarean delivery rate decreased to 31.7% in 2019 (Figure 1). Medicaid was the source of payment for 42.1% of all births in 2019. The preterm birth rate rose for the fifth straight year to 10.23% in 2019; the rate of low birthweight was essentially unchanged from 2018 at 8.31%. Twin and triplet and higher-order multiple birth rates both declined in 2019 compared with 2018.

Decreasing cerebral palsy prevalence in multiple births in the modern era: a population cohort study of European data.

Multiple births (twins or higher order multiples) are increasing in developed countries and may present higher risk for cerebral palsy (CP). However, few studies can reliably investigate trends over time because these outcomes are relatively rare. OBJECTIVE: We pooled data from European CP registers to investigate CP birth prevalence and its trends among single and multiple births born between 1990 and 2008. DESIGN: Population cohort study. SETTING: 12 population-based registers from the Surveillance of Cerebral Palsy in Europe collaboration. PARTICIPANTS: 4 446 125 single and multiple live births, of whom 8416 (0.19%) had CP of prenatal or perinatal origin. MAIN OUTCOMES: CP diagnosis ascertained in childhood using harmonised methods; CP subtype; Motor impairment severity among CP cases. RESULTS: The rate of multiple births increased from 1990. Multiples displayed higher risk for CP (RR=4.27, 95% CI 4.00 to 4.57). For singletons and multiples alike, risk for CP was higher among births of lower gestational age (GA) or birth weight (BW). However, CP birth prevalence declined significantly among very preterm (<32 weeks) and very low BW (<1500 g) multiples. Singletons and multiples with CP displayed similar severity of motor impairment. CONCLUSIONS: Between 1990 and 2008, CP birth prevalence decreased steadily among multiples with low GA or BW. Furthermore, multiples with CP display similar profiles of severe motor impairment compared with CP singletons. Improvements in management of preterm birth since the 1990s may also have been responsible for providing better prospects for multiples.

Outcomes of Infants with Very Low Birth Weight Associated with Birthplace Difference: A Retrospective Cohort Study of Births in Japan and California.

OBJECTIVE: To determine whether outcomes among infants with very low birth weight (VLBW) vary according to the birthplace (Japan or California) controlling for maternal ethnicity. STUDY DESIGN: Severe intraventricular hemorrhage (IVH) and mortality were ascertained for infants with VLBW born at 24-29 weeks of gestation during 2008-2017 and retrospectively analyzed by the country of birth for mothers and infants (Japan or California). RESULTS: Rates of severe IVH, mortality, or combined IVH/mortality were lower in the 24 095 infants born in Japan (5.1%, 5.0%, 8.8% respectively) compared with infants born in California either to 157 mothers with Japanese ethnicity (12.5%, 9.7%, 17.8%) or to a comparison group of 6173 non-Hispanic white mothers (8.4%, 8.8%, 14.6%). ORs for adverse outcomes were increased for infants born in California to mothers with Japanese ethnicity compared with infants born in Japan for severe IVH (OR, 3.31; 95% CI, 1.93-5.68), mortality (3.73; 95% CI, 2.03-6.86), and the combined outcome (3.26; 95% CI, 2.02-5.27). The odds of these outcomes also were increased for infants born in California to non-Hispanic white mothers compared with infants born in Japan. Outcomes of infants born in California did not differ by Japanese or non-Hispanic white maternal ethnicity. CONCLUSIONS: Low rates of severe IVH and mortality for infants with VLBW born in Japan were not seen in infants born in California to mothers with Japanese ethnicity. Differences in systems of regional perinatal care, social environment, and the quality of perinatal care may partially account for these differences in outcomes.

Survival and early complications of preterm infants with birthweight less than 500 grams during a 10-year period in Hungary.

BACKGROUND: There are limited data available on the survival and early complications of preterm infants with less than 500 g birthweight. To estimate the outcomes for these infants, it is important for caregivers to be aware of perinatal factors that may affect survival. OBJECTIVES: We assessed the mortality and certain early complications of preterm infants born with less than 500 g in Hungary between 2006 and 2015. METHODS: We reviewed data of 486 infants from the database of the Hungarian Central Statistical Office and in parallel of 407 infants from the "NICU database." The study period was divided into two epochs: 2006-2010 and 2011-2015. RESULTS: The survival was 27.1% in the first epoch and 39.1% in the second epoch, and the incidence of early complications was slightly higher in the second epoch. In the surviving group (first and second epoch combined), gestational age (25.1 vs 23.7 weeks), birthweight (458 vs 447 g) antenatal steroid treatment (66.3% vs 52.3%), surfactant therapy (95.1% vs 84.3%), median Apgar scores (6 vs 3 and 8 vs 5 at 1 and 5 minutes, respectively) and proportion of caesarean delivery (89.3% versus 68.5%) were higher than in the non-surviving group (first and second epoch combined). The proportion of multiple births was lower in the surviving group (15.7% vs 33.4%). CONCLUSIONS: Survival of infants with less than 500 g improved between 2006-2010 and 2011-2015 in Hungary. The slightly higher occurrence of early complications might be associated with improving survival.

The New West Japan Twins and Higher Order Multiple Births Registry.

The new West Japan Twins and Higher Order Multiple Births Registry was established by recruiting young twins and multiple births and by referrals from public health centers in the 1990s. The participants included in the survey comprised over 7800 twins and 4241 higher order multiples, and their families. Specifically, the present registry contains one of the largest triplet samples in the world. For these twins and multiples, data on year of delivery, mode of delivery, gestational age, intrapartum complications, longitudinal physical measures, motor milestones, cerebral palsy and feeding methods were obtained from records in the Maternal and Child Health Handbooks and schools. Participating mothers were asked to indicate family structure, parental educational history, maternal sleeping time, maternal health condition, maternal and paternal age at multiple delivery, complications during pregnancy, handedness of multiples and age at menarche of multiples. However, the zygosity differed among the various collaborating public health centers according to factors such as the time of investigation. Follow-up questionnaires have been mailed out every 3-4 years for longitudinal studies. This article describes the goals of this registry, recruitment of multiples and the focus of the study. The goals of this registry are not only to conduct research on human genetics and maternal and child health, but also to contribute to providing appropriate information for families with multiples.

Database of Families with Twins and Higher Order Multiples in Japanese Twins Mothers Clubs.

It is desirable for twin researchers to be aware of the needs and concerns of families of multiples and provide participants with appropriate and useful feedback and advice based on scientific evidence. Our most recent database on families with twins throughout Japan is based on a questionnaire survey conducted in 2016. Mailed questionnaires, consisting of over 500 items, were used to collect the basic data. The response rate was 38% (566/1478). This is part of a nationwide study designed to assess the long-term effect of perinatal conditions on mothers of multiples. Its aim was to study the growth and development of multiples in childhood, and for the creation of a multifetal mother and child health handbook, and to conduct a genetic epidemiologic study to test the developmental origin of health and disease hypothesis. One of the ultimate aims of this research was to provide evidence-based information on parenting of multiples for families with multiples.

Evolución temporal de los partos múltiples en Castilla y León durante 13 años / Multiple birth trends in the region of Castilla y León (Spain) in a 13 year period

Introducción: La prevalencia del embarazo múltiple está experimentando un ascenso en los últimos años, lo que conlleva un aumento de la morbimortalidad fetal y de la morbilidad materna. El objetivo de este estudio es analizar la evolución de los partos múltiples en Castilla y León durante 13 años y sus implicaciones maternas y fetales. Material y métodos: Estudio de asociación cruzada, sobre el conjunto mínimo básico de datos (CMBD), de altas hospitalarias de la red Sanidad de Castilla y León (SACYL) entre 2001 y 2013. Se realizó un análisis de tendencias mediante regresión lineal de joinpoint, un análisis ritmométrico y un análisis multivariante mediante regresión logística binaria. Resultados: A lo largo de los 13 años de estudio se observa una tendencia creciente en la proporción de partos múltiples, en contraste con los únicos, con un porcentaje anual de cambio del 3,4% (IC del 95%: 2,5-4,4%). Se encontró asociación estadística entre la edad materna, la tolerancia anormal a la glucosa, el parto operatorio, la macrosomía fetal, el parto prematuro, la muerte fetal, las malposiciones fetales, la fecundación in vitro y los estados hipertensivos maternos y el parto gemelar, destacando que la fecundación in vitro se asocia con un exceso de riesgo de 9,3 veces de parto múltiple (IC del 95%: 7,4-11,5), así como la edad de la madre se asocia con un exceso de riesgo del 5% por cada año de edad (OR: 1,05; IC 95%: 1,04-1,05). No se evidenció estacionalidad en los partos múltiples en contraposición con los únicos. Conclusiones: Los partos múltiples experimentaron un continuo ascenso, sin seguir un ritmo estacional, asociados a la extensión del uso de las técnicas de reproducción asistida y al retraso en la edad de la maternidad, lo que conlleva mayor morbimortalidad fetal y materna

Introduction: Multiple pregnancy has increased in prevalence in the last few years, which could lead to more foetal and maternal morbidity issues. The aim of this study is to describe the trend of multiple pregnancy deliveries in Castilla y León during the last 13years and the subsequent impact on foetal and maternal health. Material and methods: Data was collected from the hospital discharge reports registered in the Regional Health-care database (SACYL: Health care in Castilla y León) between 2001 and 2013. A cross sectional descriptive study was conducted, including trend analysis with log-linear joint point model, a rhythm metric study, as well as a risk assessment with multivariate analysis. Results: A pronounced upward trend was observed in the proportion of multiple deliveries in this time period, compared to single ones, with an annual percentage change of 3.4% (95% CI: 2.5-4.4). Multiple pregnancy was significantly correlated with advanced maternal age, abnormal glucose tolerance, dystocia and caesarean section delivery, premature birth, foetal malposition, foetal macrosomia, stillbirth, in vitro fertilisation, and hypertensive episodes of pregnancy. In vitro fertilization showed a 9.3 fold increased risk in multiple pregnancy (95% CI: 7.4-11.5), with maternal age increasing the risk up to 5% per year of age (OR: 1.05: 95%CI: 1.04-1.05). No seasonal rhythm was observed in multiple deliveries compared with single ones. Conclusion: Multiple pregnancy has experienced a continuous increase, with no seasonal trend, and is associated with the increase in assisted reproductive technology and advanced maternal age. This involves more problems regarding foetal and maternal morbidity and mortality

Maternal reproductive history: trends and inequalities in four population-based birth cohorts in Pelotas, Brazil, 1982-2015.

BACKGROUND: Brazil experienced important progress in maternal and child health in recent decades. We aimed at describing secular trends as well as socioeconomic and ethnic inequalities in reproductive history indicators (birth spacing, previous adverse perinatal outcome, parity and multiple births) over a 33-year span. METHODS: Four population-based birth cohort studies included all hospital births in 1982, 1993, 2004 and 2015 in Pelotas, Southern Brazil. Information on reproductive history was collected through interviews. Indicators were stratified by family income quintiles and skin colour. Absolute and relative measures of inequality were calculated. RESULTS: From 1982 to 2015, the proportion of primiparae increased from 39.2% to 49.6%, and median birth interval increased by 23.2 months. Poor women were more likely to report short intervals and higher parity, although reductions were observed in all income and ethnic groups. History of previous low birthweight was inversely related to income and increased by 7.7% points (pp) over time-more rapidly in the richest (12.1 pp) than in the poorest quintile (0.4 pp). Multiple births increased from 1.7% to 2.7%, with the highest increase observed among the richest quintile and for white women (220% and 70% increase, respectively). Absolute and relative income and ethnic-related inequalities for short birth intervals increased, whereas inequalities for previous low birthweight decreased over time. CONCLUSIONS: In this 33-year period there were increases in birth intervals, multiple births and reports of previous low-birthweight infants. These trends may be explained by increased family planning coverage, assisted reproduction and a rise in preterm births, respectively. Our results show that socioeconomic and ethnic inequalities in health are dynamic and vary over time, within the same location.

Births: Final Data for 2018.

Objectives-This report presents 2018 data on U.S. births according to a wide variety of characteristics. Trends in fertility patterns and maternal and infant characteristics are described and interpreted. Methods-Descriptive tabulations of data reported on the birth certificates of the 3.79 million births that occurred in 2018 are presented. Data are presented for maternal age, live-birth order, race and Hispanic origin, marital status, tobacco use, prenatal care, source of payment for the delivery, method of delivery, gestational age, birthweight, and plurality. Selected data by mother's state of residence and birth rates by age also are shown. Trend data for 2010 through 2018 are presented for selected items. Trend data by race and Hispanic origin are shown for 2016-2018. Results-3,791,712 births were registered in the United States in 2018, down 2% from 2017. Compared with rates in 2017, the general fertility rate declined to 59.1 births per 1,000 women aged 15-44. The birth rate for females aged 15-19 fell 7% in 2018. Birth rates declined for women aged 20-34 and increased for women aged 35-44. The total fertility rate declined to 1,729.5 births per 1,000 women in 2018. Birth rates for both married and unmarried women declined from 2017 to 2018. The percentage of women who began prenatal care in the first trimester of pregnancy rose to 77.5% in 2018; the percentage of all women who smoked during pregnancy declined to 6.5%. The cesarean delivery rate decreased to 31.9% in 2018 following an increase in 2017. Medicaid was the source of payment for 42.3% of all 2018 births, down 2% from 2017. The preterm birth rate rose for the fourth straight year to 10.02% in 2018; the rate of low birthweight was unchanged at 8.28%. Twin and triplet and higher-order multiple birth rates declined in 2018 (Figure 1).

[Multiple birth trends in the region of Castilla y León (Spain) in a 13 year period]. / Evolución temporal de los partos múltiples en Castilla y León durante 13 años.

INTRODUCTION: Multiple pregnancy has increased in prevalence in the last few years, which could lead to more foetal and maternal morbidity issues. The aim of this study is to describe the trend of multiple pregnancy deliveries in Castilla y León during the last 13years and the subsequent impact on foetal and maternal health. MATERIAL AND METHODS: Data was collected from the hospital discharge reports registered in the Regional Health-care database (SACYL: Health care in Castilla y León) between 2001 and 2013. A cross sectional descriptive study was conducted, including trend analysis with log-linear joint point model, a rhythm metric study, as well as a risk assessment with multivariate analysis. RESULTS: A pronounced upward trend was observed in the proportion of multiple deliveries in this time period, compared to single ones, with an annual percentage change of 3.4% (95% CI: 2.5-4.4). Multiple pregnancy was significantly correlated with advanced maternal age, abnormal glucose tolerance, dystocia and caesarean section delivery, premature birth, foetal malposition, foetal macrosomia, stillbirth, in vitro fertilisation, and hypertensive episodes of pregnancy. In vitro fertilization showed a 9.3 fold increased risk in multiple pregnancy (95% CI: 7.4-11.5), with maternal age increasing the risk up to 5% per year of age (OR: 1.05: 95%CI: 1.04-1.05). No seasonal rhythm was observed in multiple deliveries compared with single ones. CONCLUSION: Multiple pregnancy has experienced a continuous increase, with no seasonal trend, and is associated with the increase in assisted reproductive technology and advanced maternal age. This involves more problems regarding foetal and maternal morbidity and mortality.

Delayed Childbearing as a Growing, Previously Unrecognized Contributor to the National Plural Birth Excess.

OBJECTIVE: To establish the annual and cumulative multiyear contribution of delayed childbearing to the national plural birth excess. METHODS: Using publicly available national birth data reported by the National Center for Health Statistics, we estimated the contribution of delayed childbearing to the national plural birth excess through 2016. To this end, the observed as well as the maternal age- and race-adjusted national plural birth rates were assessed before (1949-1966; n=71,570,717) and during (1971-2016; n=166,817,655) the assisted reproduction era. Comparable estimates through 2025 relied on simulated projections. RESULTS: The relative risk estimates of unassisted plural births by maternal age before the assisted reproduction era (1949-1966) proved unimodal and race-dependent. The risk of unassisted plural births in 35- to 39-year-old black women proved 2.75-fold higher than that of 15- to 19-year-old counterparts (39.81/1,000 to 14.48/1,000; 95% CI 2.67-2.83). A 2.47-fold risk increment was noted for comparably aged white women (28.76/1,000 to 11.63/1,000; 95% CI 2.43-2.52). Similar age-dependent risk increments were obtained for twin and higher order births. An increasingly prominent delayed childbearing trend during the assisted reproduction era (1971-2016) gave rise to 255,964 (95% CI 134,746-375,581) and 66,271 (95% CI 34,099-96,197) unassisted plural births by white and black women, respectively. In 2016 alone, delayed childbearing accounted for 24% (95% CI 15-32%) and 38% (95% CI 28-47%) of the national plural birth excess for white and black women, respectively. By 2025, delayed childbearing could account for as much as 46% (95% CI 32-60%) and 40% (95% CI 30-53%) of the national plural birth excess for white and black women, respectively. CONCLUSION: Delayed childbearing, a growing contributor to the national plural birth excess previously solely ascribed to assisted reproduction, warrants greater consideration in future clinical, analytic, and policy deliberations as well as in individual family planning decisions.

Births: Final Data for 2016.

This report presents 2016 data on U.S. births according to a wide variety of characteristics. Trends in fertility patterns and maternal and infant characteristics are described and interpreted.Descriptive tabulations of data reported on the birth certificates of the 3.95 million births that occurred in 2016 are presented. Data are presented for maternal age, live-birth order, race and Hispanic origin, marital status, tobacco use, prenatal care, source of payment for the delivery, method of delivery, gestational age, birthweight, and plurality. Selected data by mother's state of residence and birth rates by age also are shown. Trend data for 2010-2016 are presented for selected items. A total of 3,945,875 births were registered in the United States in 2016, down 1% from 2015. Compared with rates in 2015, the general fertility rate declined to 62.0 per 1,000 women aged 15-44. The birth rate for females aged 15-19 fell 9% in 2016. Birth rates declined for women in their 20s but increased for women intheir 30s and early 40s. The total fertility rate declined to 1,820.5 births per 1,000 women in 2016. The birth rate for unmarried women declined, while the rate for married women increased. More than three-quarters of women began prenatal care in the firsttrimester of pregnancy (77.1%) in 2016, while 7.2% of all women smoked during pregnancy. The cesarean delivery rate declined for the fourth year in a row. Medicaid was the source of payment for 42.6% of all 2016 births. The preterm birth rate rose for the second straight year, and the rate of low birthweight increased 1%. Twin and triplet and higher-order multiple birth rates declined, although the changes were not statistically significant.

Aspects of the History of Twin Research: Statistical Congresses in the 19th Century and Hellin's Law.

In the 19th century, a series of international statistical congresses began that were important for population studies, including twin research. The introduction of common rules for the national demographic registers enabled scientists to contribute to the genesis of statistical research. The congress in St. Petersburg in 1872, in particular, focused on the movements of the population, and how they should be registered. Among the facts to be recorded were in multiple births, the sex and number of children born alive or still-born, whether legitimate or illegitimate, and the age of the mother at the date of the births. During the history of twin research, Hellin's law has played a central role because it is an approximately correct association between the rates of multiple maternities. It has been mathematically proven that Hellin's law does not hold as a general rule. Analyses show divergences from the law that are difficult to explain and/or eliminate. Varying improvements of this law have been proposed. The majority of all studies of Hellin's law are based on empirical rates of multiple maternities, ignoring random errors. Such studies can never confirm the law, but only identify errors with respect to Hellin's law that are too large to be characterized as random. It is of particular interest to note and explain why the rates of higher multiple maternities are sometimes too high or too low when Hellin's law is used as a benchmark. Studies have shown that there were investigators before Hellin who have contributed substantially to Hellin's law. In this article, we re-examine some old data sets and contributions in which Hellin's law has been evaluated and also analyze recent data.