Divergent age patterns of under-5 mortality in south Asia and sub-Saharan Africa: a modelling study.

BACKGROUND: Understanding the age pattern of under-5 mortality is essential for identifying the most vulnerable ages and underlying causes of death, and for assessing why the decline in child mortality is slower in some countries and subnational areas than others. The aim of this study is to detect age patterns of under-5 mortality that are specific to low-income and middle-income countries (LMICs). METHODS: In this modelling study, we used data from 277 Demographic and Health Surveys (DHSs), 58 Health and Demographic Surveillance Systems (HDSSs), two cohort studies, and two sample-registration systems. From these sources, we collected child date of birth and date of death (or age at death) from LMICs between 1966 and 2020. We computed 22 deaths rates from each survey with the following age breakdowns: 0, 7, 14, 21, and 28 days; 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 15, 18, and 21 months; and 2, 3, 4, and 5 years. We assessed how probabilities of dying estimated for the 22 age groups deviated from predictions generated by a vital registration model that reflects the historical mortality of 25 high-income countries. FINDINGS: We calculated mortality rates of 81 LMICs between 1966 and 2020. In contrast with the other regions of the world, we found that under-5 mortality in south Asia and sub-Saharan Africa was characterised by increased mortality at both ends of the age range (ie, younger than 28 days and older than 6 months) at a given level of mortality. Observed mortality in these regions was up to 2 times higher than predicted by the vital registration model for the younger-than-28 days age bracket, and up to 10 times higher than predicted for the older-than-6 months age bracket. This age pattern of under-5 mortality is significant in 17 countries in south Asia and sub-Saharan Africa. Excess mortality in children older than 6 months without excess mortality in children younger than 28 days was found in 38 countries. In south Asia, results were consistent across data sources. In sub-Saharan Africa, excess mortality in children younger than 28 days was found mostly in DHSs; the majority of HDSSs did not show this excess mortality. We have attributed this difference in data sources mainly to omissions of early deaths in HDSSs. INTERPRETATION: In countries with age patterns of under-5 mortality that diverge from predictions, evidence-based public health interventions should focus on the causes of excess of mortality; notably, the effect of fetal growth restriction and infectious diseases. The age pattern of under-5 mortality will be instrumental in assessing progress towards the decline of under-5 mortality and the Sustainable Development Goals. FUNDING: Eunice Kennedy Shriver National Institute of Child Health and Human Development of the National Institutes of Health.

Twin Peaks: more twinning in humans than ever before.

STUDY QUESTION: How many twins are born in human populations and how has this changed over recent decades? SUMMARY ANSWER: Since the 1980s, the global twinning rate has increased by a third, from 9.1 to 12.0 twin deliveries per 1000 deliveries, to about 1.6 million twin pairs each year. WHAT IS KNOWN ALREADY: It was already known that in the 1980s natural twinning rates were low in (East) Asia and South America, at an intermediate level in Europe and North America, and high in many African countries. It was also known that in recent decades, twinning rates have been increasing in the wealthier parts of our world as a result of the rise in medically assisted reproduction (MAR) and delayed childbearing. STUDY DESIGN, SIZE, DURATION: We have brought together all information on national twinning rates available from statistical offices, demographic research institutes, individual survey data and the medical literature for the 1980-1985 and the 2010-2015 periods. PARTICIPANTS/MATERIALS, SETTING, METHODS: For 165 countries, covering over 99% of the global population, we were able to collect or estimate twinning rates for the 2010-2015 period. For 112 countries, we were also able to obtain twinning rates for 1980-1985. MAIN RESULTS AND THE ROLE OF CHANCE: Substantial increases in twinning rates were observed in many countries in Europe, North America and Asia. For 74 out of 112 countries the increase was more than 10%. Africa is still the continent with highest twinning rates, but Europe, North America and Oceania are catching up rapidly. Asia and Africa are currently home to 80% of all twin deliveries in the world. LIMITATIONS, REASONS FOR CAUTION: For some countries, data were derived from reports and papers based on hospital registrations which are less representative for the country as a whole than data based on public administrations and national surveys. WIDER IMPLICATIONS OF THE FINDINGS: The absolute and relative number of twins for the world as a whole is peaking at an unprecedented level. An important reason for this is the tremendous increase in medically assisted reproduction in recent decades. This is highly relevant, as twin deliveries are associated with higher infant and child mortality rates and increased complications for mother and child during pregnancy and during and after delivery. STUDY FUNDING/COMPETING INTEREST(S): The contribution of CM was partially supported by the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Programme (grant No 681546, FAMSIZEMATTERS), Nuffield College, and the Leverhulme Trust. The contribution of GP was partially supported by the French Agence Nationale de la Recherche (grant No ANR-18-CE36-0007-07). The authors declare no conflict of interest. TRIAL REGISTRATION NUMBER: N/A.

Errors in reported ages and dates in surveys of adult mortality: A record linkage study in Niakhar (Senegal).

Sibling survival histories are a major source of adult mortality estimates in countries with incomplete death registration. We evaluate age and date reporting errors in sibling histories collected during a validation study in the Niakhar Health and Demographic Surveillance System (Senegal). Participants were randomly assigned to either the Demographic and Health Survey questionnaire or a questionnaire incorporating an event history calendar, recall cues, and increased probing strategies. We linked 60-62 per cent of survey reports of siblings to the reference database using manual and probabilistic approaches. Both questionnaires showed high sensitivity (>96 per cent) and specificity (>97 per cent) in recording siblings' vital status. Respondents underestimated the age of living siblings, and age at and time since death of deceased siblings. These reporting errors introduced downward biases in mortality estimates. The revised questionnaire improved reporting of age of living siblings but not of age at or timing of deaths.

Inequalities in cause-specific mortality in children and adolescents in the Moramanga health survey, Madagascar.

OBJECTIVES: One child or young adolescent dies every 10 min in Madagascar and large disparities in survival persist. We estimated cause-specific mortality in a cohort of children aged 0-14 in the Moramanga district and explored how causes of death shape these inequalities. METHODS: Children were followed prospectively between 2012 and 2017. Causes of death were established based on verbal autopsies. Incidence rate ratios were estimated in Poisson regression models. RESULTS: The risk of dying before age 15 was 68.1 per thousand live births. Risks of dying were highest in the first year of life (31.2‰) and lowest in children aged 10-14 (6.4‰). The male-to-female sex ratios of mortality increased with age and reached 2.3 among adolescents aged 10-14. Communicable, nutritional and neonatal causes accounted for 79.5% of deaths below age 5 and 47.0% above age 5. Mortality was positively associated with household poverty, lack of education of the household head, and rural residence. CONCLUSIONS: Interventions should be designed with an equity lens to reduce large disparities in survival and be tailored to the needs of each age-group.

Estimating cause-specific mortality in Madagascar: an evaluation of death notification data from the capital city.

BACKGROUND: Trends in cause-specific mortality in most African countries are currently estimated from epidemiological models because the coverage of the civil registration system is low and national statistics on causes of death are unreliable at the national level. We aim to evaluate the performance of the death notification system in Antananarivo, the capital city of Madagascar, to inform cause-of-death statistics. METHODS: Information on the sex of the deceased, dates of birth and death, and underlying cause of death were transcribed from death registers maintained in Antananarivo. Causes of death were coded in ICD-9 and mapped to cause categories from the Global Burden of Disease 2016 Study (GBD). The performance of the notification system was assessed based on the Vital Statistics Performance Index, including six dimensions: completeness of death registration, quality of cause of death reporting, quality of age and sex reporting, internal consistency, level of cause-specific detail, and data availability and timeliness. We redistributed garbage codes and compared cause-specific mortality fractions in death records and estimates from the GBD with concordance correlation coefficients. RESULTS: The death notification system in Antananarivo performed well on most dimensions, although 31% of all deaths registered over the period 1976-2015 were assigned to ICD codes considered as "major garbage codes" in the GBD 2016. The completeness of death notification, estimated with indirect demographic techniques, was higher than 90% in the period 1975-1993, and recent under-five mortality rates were consistent with estimates from Demographic and Health Surveys referring to the capital city. After redistributing garbage codes, cause-specific mortality fractions derived from death notification data were consistent with GBD 2016 for the whole country in the 1990s, with concordance correlation coefficients higher than 90%. There were larger deviations in recent years, with concordance correlation coefficients in 2015 at 0.74 (95% CI 0.66-0.81) for men and 0.81 (95% CI 0.74-0.86) for women. CONCLUSIONS: Death notification in Antananarivo is a low-cost data source allowing real-time mortality monitoring, with a potential to improve disease burden estimates. Further efforts should be directed towards evaluating data quality in urban centers in Madagascar and other African countries to fill important data gaps on causes of death.

Returning home to die or leaving home to seek health care? Location of death of urban and rural residents in Burkina Faso and Senegal.

BACKGROUND: In sub-Saharan Africa, the literature on end of life is limited and focuses on place of death as an indicator of access and utilization of health-care resources. Little is known about population mobility at the end of life. OBJECTIVE: To document the magnitude, motivations and associated factors of short-term mobility before death among adults over 15 years of age in Burkina Faso and Senegal. METHODS: The study was based on deaths of adult residents reported in three Health and Demographic Surveillance System (HDSS) sites in urban (Ouagadougou) and semi-rural areas (Kaya) of Burkina Faso, and rural areas of Senegal (Mlomp). After excluding deaths from external causes, the analysis covered, respectively, 536 and 695 deaths recorded during the period 2012-2015 in Ouagadougou and Kaya. The period was extended to 2000-2015 in Mlomp, with a sample of 708 deaths. Binary logistic regressions were used to examine the effects of socio-demographic characteristics on place of death (health facility or not) and location of death (within or outside the HDSS). RESULTS: In Mlomp, Kaya and Ouagadougou, respectively 20.6%, 5.3% and 5.9% of adults died outside the HDSS site. In Mlomp and Kaya, these deaths were more likely to occur in a health facility than deaths that occurred within the site. The reverse situation was found in Ouagadougou. Age is the strongest determinant of mobility before death in Mlomp and Kaya. In Mlomp, young adults (15-39) were 10 times more likely to die outside the site than adults in the 60-79 age group. In Ouagadougou, non-natives were three times more likely to die outside the city than natives. CONCLUSIONS: At the end of life, some rural residents move to urban areas for medical treatment while some urban dwellers return to their village for supportive care. These movements of dying individuals may affect the estimation of urban/rural mortality differentials.

Improving survey data on pregnancy-related deaths in low-and middle-income countries: a validation study in Senegal.

OBJECTIVE: In low- and middle-income countries (LMICs), siblings' survival histories (SSH) are often used to estimate maternal mortality, but SSH data on causes of death at reproductive ages have seldom been validated. We compared the accuracy of two SSH instruments: the standard questionnaire used during the demographic and health surveys (DHS) and the siblings' survival calendar (SSC), a new questionnaire designed to improve survey reports of deaths among women of reproductive ages. METHODS: We recruited 1189 respondents in a SSH survey in Niakhar, Senegal. Mortality records from a health and demographic surveillance system (HDSS) constituted the reference data set. Respondents were randomly assigned to an interview with the DHS or SSC questionnaires. A total of 164 respondents had a sister who died at reproductive ages over the past 15 years before the survey according to the HDSS. RESULTS: The DHS questionnaire led to selective omissions of deaths: DHS respondents were significantly more likely to report their sister's death if she had died of pregnancy-related causes than if she had died of other causes (96.4% vs. 70.9%, P < 0.007). Among reported deaths, both questionnaires had high sensitivity (>90%) in recording pregnancy-related deaths. But the DHS questionnaire had significantly lower specificity than the SSC (79.5% vs. 95.0%, P = 0.015). The DHS questionnaire overestimated the proportion of deaths due to pregnancy-related causes, whereas the SSC yielded unbiased estimates of this parameter. CONCLUSION: Statistical models informed by SSH data collected using the DHS questionnaire might exaggerate maternal mortality in Senegal and similar settings. A new questionnaire, the SSC, could permit better tracking progress towards the reduction in maternal mortality.

Improving the quality of adult mortality data collected in demographic surveys: validation study of a new siblings' survival questionnaire in Niakhar, Senegal.

BACKGROUND: In countries with limited vital registration, adult mortality is frequently estimated using siblings' survival histories (SSHs) collected during Demographic and Health Surveys (DHS). These data are affected by reporting errors. We developed a new SSH questionnaire, the siblings' survival calendar (SSC). It incorporates supplementary interviewing techniques to limit omissions of siblings and uses an event history calendar to improve reports of dates and ages. We hypothesized that the SSC would improve the quality of adult mortality data. METHODS AND FINDINGS: We conducted a retrospective validation study among the population of the Niakhar Health and Demographic Surveillance System in Senegal. We randomly assigned men and women aged 15-59 y to an interview with either the DHS questionnaire or the SSC. We compared SSHs collected in each group to prospective data on adult mortality collected in Niakhar. The SSC reduced respondents' tendency to round reports of dates and ages to the nearest multiple of five or ten ("heaping"). The SSC also had higher sensitivity in recording adult female deaths: among respondents whose sister(s) had died at an adult age in the past 15 y, 89.6% reported an adult female death during SSC interviews versus 75.6% in DHS interviews (p = 0.027). The specificity of the SSC was similar to that of the DHS questionnaire, i.e., it did not increase the number of false reports of deaths. However, the SSC did not improve the reporting of adult deaths among the brothers of respondents. Study limitations include sample selectivity, limited external validity, and multiple testing. CONCLUSIONS: The SSC has the potential to collect more accurate SSHs than the questionnaire used in DHS. Further research is needed to assess the effects of the SSC on estimates of adult mortality rates. Additional validation studies should be conducted in different social and epidemiological settings. TRIAL REGISTRATION: Controlled-Trials.com ISRCTN06849961

The epidemiological transition in Antananarivo, Madagascar: an assessment based on death registers (1900-2012).

BACKGROUND: Madagascar today has one of the highest life expectancies in sub-Saharan Africa, despite being among the poorest countries in the continent. There are relatively few detailed accounts of the epidemiological transition in this country due to the lack of a comprehensive death registration system at the national level. However, in Madagascar's capital city, death registration was established around the start of the 20th century and is now considered virtually complete. OBJECTIVE: We provide an overview of trends in all-cause and cause-specific mortality in Antananarivo to document the timing and pace of the mortality decline and the changes in the cause-of-death structure. DESIGN: Death registers covering the period 1976-2012 were digitized and the population at risk of dying was estimated from available censuses and surveys. Trends for the period 1900-1976 were partly reconstructed from published sources. RESULTS: The crude death rate stagnated around 30‰ until the 1940s in Antananarivo. Mortality declined rapidly after the World War II and then resurged again in the 1980s as a result of the re-emergence of malaria and the collapse of Madagascar's economy. Over the past 30 years, impressive gains in life expectancy have been registered thanks to the unabated decline in child mortality, despite political instability, a lasting economic crisis and the persistence of high rates of chronic malnutrition. Progress in adult survival has been more modest because reductions in infectious diseases and diseases of the respiratory system have been partly offset by increases in cardiovascular diseases, neoplasms, and other diseases, particularly at age 50 years and over. CONCLUSIONS: The transition in Antananarivo has been protracted and largely dependent on anti-microbial and anti-parasitic medicine. The capital city now faces a double burden of communicable and non-communicable diseases. The ongoing registration of deaths in the capital generates a unique database to evaluate the performance of the health system and measure intervention impacts.

Health & demographic surveillance system profile: Bandafassi Health and Demographic Surveillance System (Bandafassi HDSS), Senegal.

The Bandafassi Health and Demographic Surveillance System (Bandafassi HDSS) is located in south-eastern Senegal, near the borders with Mali and Guinea. The area is 700 km from the national capital, Dakar. The population under surveillance is rural and in 2012 comprised 13 378 inhabitants living in 42 villages. Established in 1970, originally for genetic studies, and initially covering only villages inhabited by one subgroup of the population of the area (the Mandinka), the project was transformed a few years later into a HDSS and then extended to the two other subgroups living in the area: Fula villages in 1975, and Bedik villages in 1980. Data have been collected through annual rounds since the project first began. On each visit, investigators review the composition of all the households, checking the lists of people who were present in each household the previous year and gathering information about births, marriages, migrations and deaths (including their causes) since then. One specific feature of the Bandafassi HDSS is the availability of genealogies.

Reporting errors in siblings' survival histories and their impact on adult mortality estimates: results from a record linkage study in Senegal.

Estimates of adult mortality in countries with limited vital registration (e.g., sub-Saharan Africa) are often derived from information about the survival of a respondent's siblings. We evaluated the completeness and accuracy of such data through a record linkage study conducted in Bandafassi, located in southeastern Senegal. We linked at the individual level retrospective siblings' survival histories (SSH) reported by female respondents (n = 268) to prospective mortality data and genealogies collected through a health and demographic surveillance system (HDSS). Respondents often reported inaccurate lists of siblings. Additions to these lists were uncommon, but omissions were frequent: respondents omitted 3.8 % of their live sisters, 9.1 % of their deceased sisters, and 16.6 % of their sisters who had migrated out of the DSS area. Respondents underestimated the age at death of the siblings they reported during the interview, particularly among siblings who had died at older ages (≥45 years). Restricting SSH data to person-years and events having occurred during a recent reference period reduced list errors but not age and date errors. Overall, SSH data led to a 20 % underestimate of 45 q 15 relative to HDSS data. Our study suggests new quality improvement strategies for SSH data and demonstrates the potential use of HDSS data for the validation of "unconventional" demographic techniques.

Divergences in trends in child and adult mortality in sub-Saharan Africa: survey evidence on the survival of children and siblings.

This paper provides an overview of trends in mortality in children aged under 5 and adults between the ages of 15 and 60 in sub-Saharan Africa, using data on the survival of the children and siblings collected in Demographic and Health Surveys. If conspicuous stalls in the 1990s are disregarded, child mortality levels have generally declined and converged over the last 30-40 years. In contrast, adult mortality in many East and Southern African countries has increased markedly, echoing earlier increases in the incidence of HIV. In recent years, adult mortality levels have begun to decline once again in East Africa, in some instances before the large-scale expansion of antiretroviral therapy programmes. More surprising is the lack of sustained improvements in adult survival in some countries that have not experienced severe HIV epidemics. Because trends in child and adult mortality do not always evolve in tandem, we argue that model-based estimates, inferred by matching indices of child survival onto standard mortality schedules, can be very misleading.

Misclassification of pregnancy-related deaths in adult mortality surveys: case study in Senegal.

OBJECTIVE: In countries with limited vital registration data, maternal mortality levels are often estimated using siblings' survival histories (SSH) collected during retrospective adult mortality surveys. We explored how accurately adult deaths can be classified as pregnancy related using such data. METHOD: The study was conducted in a rural area of south-eastern Senegal with high maternal mortality, Bandafassi. We used data from a demographic surveillance system (DSS) in this area to identify deaths of women at reproductive ages between 2003 and 2009 and to locate the surviving adult sisters of the deceased and interview them. Siblings' survival histories were linked at the individual level to death records, and verbal autopsy data obtained by the demographic surveillance system. We compared the classification of adult female deaths as pregnancy related or not in interviews and DSS records. RESULTS: There were 91 deaths at reproductive ages in the Bandafassi DSS between 2003 and 2009, but only 59 had known surviving sisters. Some deaths were omitted by respondents, or reported as alive or as having occurred during childhood (n = 8). Among deaths reported both in the SSH and DSS data, 94% of deaths classified as pregnancy related in the DSS data were also classified as such by siblings' survival histories. Only 70% of deaths classified as not pregnancy related in the DSS data were also classified as such by siblings' survival histories. CONCLUSION: Misclassifications of pregnancy-related deaths in retrospective adult mortality surveys may affect estimates of pregnancy-related mortality rates.

Religious Differences in Child Vaccination Rates in Urban Africa: Comparison of Population Surveillance Data from Ouagadougou; Burkina Faso

Many studies have shown a significant relationship between religion and health in Western countries. In developing countries; however; there is a dearth of scientific studies on the matter. Using data from the Ouagadougou Health and Demographic Surveillance System; this paper examines religious differences in child vaccination rates in five districts of Ouagadougou; Burkina Faso. It tests the applicability of the selectivity hypothesis; which holds that religious differences in health come from underlying differences in the socioeconomic and demographic composition of religious communities. In our study population; even when socioeconomic and demographic characteristics are taken into account; an effect of religion on child vaccination rates was observed. This suggests that religious disparities in child vaccination rates are not solely due to the makeup of different religious communities; but also to ideological differences and/or to diffusion effects from interactions within religious groups. The religious differences demonstrated here suggest that a greater emphasis should be put on community-based approaches involving religious leaders when addressing health disparities

[Are the attitudes associated with the mother and HIV/AIDS responsible for the rise in infant mortality recorded in Cote d'Ivoire in the 1990s?]. / Les attitudes liées àla mère et le VIH/SIDA sont-ils responsables de la remontée de la mortalité des enfants observée en Côte d'Ivoire durant la décennie 1990?

Demographic and Health Surveys conducted in the 1990s in Côte d'Ivoire suggest a resurgence of mortality during this period. This article examines the responsibility of mother attitudes and HIV/AIDS pandemic in the increase of mortality recorded. The rise in mortality was discernible between the first and second DHS, so we tried to find out whether there have been, between the two periods, negative changes in child survival factors associated with mother attitudes and HIV/AIDS pandemic. Whether it has to do with antenatal visits, birthing places, mother and child vaccination or breastfeeding, there is an improvement in the practices of women mothers. The HIV-related mortality has certainly increased over the decade but the improvement on the part of infant mortality is not statistically significant between the two observations.

[Assessment of 24 years of infant growth monitoring in a rural area of Senegal (1969-1992)]. / Bilan de 24 années de suivi pondéral de nourrissons d'une zone rurale au Sénégal (1969-1992).

UNLABELLED: Undernutrition in young children in developing countries is associated with an increased risk of death. But in several studies, a decrease in mortality was not associated with any decrease in the prevalence of undernutrition. STUDY AREA: A rural population of Casamance (Senegal) has been under yearly demographic surveillance by The French National Institute of Demographic Studies (INED) since 1985. Between 1960-1964 and 1990-1994, under-5 and child (1-4 years) mortality rates dropped from 312 to 127 and from 201 to 68 per 1,000, respectively. Since 1961, French Catholic nuns who are also professional nurses have been in charge of a private village dispensary located in a rural area of Casamance. This dispensary delivers permanent, high quality service and is widely attended. GROWTH MONITORING PROGRAMME: A growth-monitoring programme, supported by Cathwell, was initiated in 1969 for 0-5-year-old children (0-3 from 1985). Children were weighed wearing light clothes to the nearest 10g. Weights were recorded in a register that also contained information concerning identity (name, sex, date of birth) and address. All weights were plotted on growth charts kept by the mothers. During the sessions, the nurses provided nutrition education messages (i.e., preparation of high-energy and nutrient-dense infant gruels using local foods), advice on illness management (oral rehydration during diarrhoea) and hygiene (well and water-jar disinfection, construction of pit-latrines), importance of vaccination. From 1975, they also distributed free chloroquine during the malaria transmission season (May-November) for prevention and early presumptive treatment. Most likely thanks to this programme, infant and child mortality reached a low level at the end of the 1980s. In 1990, plasmodium resistance to chloroquine appeared, increasing malaria mortality. METHODS: All weight measurements taken in 1969-1994 were entered into a database. This paper presents an analysis of weight measurements taken at 3-23 months of age from 1969-1992. A total of 4,636 infants were weighed at least once, but only 3,912 infants (1,983 boys and 1,929 girls) were available for the analysis, 724 being excluded due to missing data. RESULTS: The average coverage of the programme during the month of February was 88% for infants aged 3-23 months. Mean weight was examined at three target ages: 5, 11 and 15 months. Not only did the nutritional status not improve between 1969 and 1989, it even deteriorated in some years for all three age-cohorts. The nutritional status of infants in this community did not differ significantly from that of 12-23 month-old Senegalese children in the 1992-1993 Demographic and Health Survey (DHS). Seasonal differences in mean weight and the prevalence of underweight became significant in the rainy season since 1975. Underweight for the 15-month-old children increased over time during the rainy season. These findings were unexpected, since malaria morbidity is thought to be at least partially responsible for seasonal variations in the nutritional status of young children, and despite the fact that the nurses began a malaria control programme in 1975. CONCLUSION: The rapid transition towards lower childhood mortality observed in this rural area of Casamance (Senegal), was not concomitant with any improvement in infants' nutritional status from 1969 through 1992. Focused public health interventions such as vaccinations and malaria prevention probably did not improve the nutritional status. Paradoxically, growth monitoring may have been more helpful in improving health than growth. Targeted specific nutritional interventions are needed to significantly improve growth of children in this community.

Frequency of twin births in developed countries.

Twinning rates in developed countries have recently registered an increase. At the end of the 1970s, the change in mother's age structure has partially contributed to the growth in the proportion of multiple births. In fact, the evolution of twinning rates is related to the calendar of maternity since, comparatively to younger mothers, older women more frequently have twins. Moreover, the growing frequency of multiple births also depends on fertility treatments, which are largely used in the developed countries. National data from the civil birth registration systems are taken into account in order to describe, in a comparative study, the main trends of twinning rates in the 20th century.