Catalina Torres, Arianna Caporali and Gilles Pison

We’ve been researching developments in birth rates of twins for several years to learn what they are in different countries and understand how they are evolving. The French Institute for Demographic Studies or INED is conducting this project in partnership with France’s Museum of Natural History, and the project is funded by the Agence Nationale de la Recherche.

We worked to obtain all information published by national statistics institutes in their statistical yearbooks and on their contemporary websites, information which we then compiled in a database. INED’s DataLab was involved in the project from the outset. 

For the last 50 years, the frequency of twin and multiple births has been rising in developed countries as never before. In France, for example, the birth rate for twins has doubled, rising from fewer than 9 in a thousand deliveries in the early 1970s to over 17 per thousand in the early 2010s.

Two factors are driving the twin birth boom. First, the probability of being pregnant with twins rises with mothers’ age, and women are having children increasingly late in life. Second, the use of assisted reproduction technology is also rising, and the pregnancies thus obtained are more likely to be multiple that are unassisted pregnancies. 

The twin birth boom is a public health problem. Twins are more fragile than singletons; they are more likely to be premature and underweight. And twin births involve more delivery complications, which can have lasting effects on the twins. 

The database contains time series on annual numbers of singleton, twin, triplet, and quadruplet-or-more births, as well rates of twin and other multiple births, for 25 countries with reliable statistics on the matter. 

The database was designed for complete open access. To facilitate the use of this information, we provide highly detailed documents indicated the quality of each national series, the definitions used, as well as the sources and source locations. The program codes developed for data checking and processing may also be downloaded, enabling users to reconstitute corrected series. We also included an interactive visualization tool, which makes it easier to explore the data online.

We hope the prize will increase visibility for the database. It also encourages us to continue the work and update the data, which will require adding recent data to the series as they’re released by national statistics institutes. And for INED’s DataLab, HMBD stands as a model for developing other databases.

The database mainly targets those parts of the scientific community studying reproduction biology, medicine, and behaviors, and who are particularly interested in birth and family trends, child health, and medically assisted procreation. But it is also for a wider public; groups of parents with twins, for example, who are naturally interested in anything pertaining to multiple births. In fact, two of those groups are project partners: France’s Fédération Jumeaux et Plus [Twins and More], and the International Council of Multiple Birth Organizations, an umbrella organization for national groups across the world.