Data and metadata

Download the most recent version of the HMBD

HMBD (v.1) - last update: 18/07/2023 [ZIP | 140.0 K.o.]

11/08/2022: The variable Flag was removed in this data update, as we are currently replacing it by the variable Footnotes. These variables are available in the country-specific input data files. 

The data available in the HMBD have been verified and corrected if necessary, e.g. when inconsistencies were identified in the input data. In addition, the values for certain variables in the HMBD are the result of calculations based on the verified and corrected input data available for each country and source.  Detailed calculations by country can be consulted in the R-code files.

See the description of the variables available in the HMBD

Table 1. Variables available in the HMBD
Variable name Description
Country Country name
Source Code of the data source. The complete list of references is available in the documentation of the HMBD. 
Year Year of reference of the data

Indicates whether the cases with still born children are included in the data:

0 = No (stillbirths not included);

1 = Yes (stillbirths included); 

2 = Mixed (stillbirths included in some cases only); 

99 = Information not available

Singletons Number of single deliveries
Twin_deliveries Number of twin deliveries
Triplet_deliveries* Number of triplet deliveries
Quadruplet_plus_deliveries* Number of deliveries involving four or more children
Multiple_deliveries Total number of multiple deliveries (i.e. the sum of twin, triplet, and quadruplet + deliveries)
Multiple_children Number of children born from multiple deliveries (twin babies, triplet babies, etc.)
Total_deliveries Total number of deliveries (i.e., single and multiple deliveries combined)
Twinning_rate Number of twin deliveries / total number of deliveries, per 1,000.
Multiple_rate Number of multiple deliveries / total number of deliveries, per 1,000.

Indicates caution. For the cases with Flag = 1, data users are advised to read the notes and warnings for the concerned year and/or data source available in the country-specific metadata file (sheet ’metadata - sources & notes’): 

0 = No warnings identified

1 = Warnings should be consulted

* In some cases, the column Triplet_deliveries may also include the number of quadruplets and more children. This occurs when it is impossible to distinguish the deliveries by number of children (among the deliveries involving at least three children) in the original data sources. These cases are indicated in the country-specific metadata files.

** The variable Flag, available in previous releases of the HMBD, will be replaced by the variable Footnotes (examples are available for those countries with metadata files using the new format, see Metadata section).


Metadata and input data by country

A Australia, Austria
C Canada, Chile, Czech Republic
D Denmark
E England and Wales
F Finland, France
G Germany, Greece
I Iceland, Italy
J Japan
L Lithuania
N Netherlands, New Zealand, Norway
R Republic of Korea
S Scotland, Spain, Sweden, Switzerland
U United States, Uruguay

We are currently introducing a new format for the metadata files. Metadata with the new format are already available for Australia, Austria, the Czech Republic, England and Wales, France, New Zealand, Spain, the United States, and Uruguay. For the other countries, the new format will be implemented gradually. 

Supplemental data

The references to other data sources with detailed data on multiple births according to certain characteristics (sex-composition, mother’s age, etc.) are available here. This list is not exhaustive, and it is frequently updated.

Explore the data in the HMBD

HMBD data explorer: This tool allows you to easily explore the data by country in the HMBD

A detailed description of the HMBD is available in:

Torres, C., Caporali, A., Pison, G. (2023). The Human Multiple Births Database (HMBD): An international database on twin and other multiple births. Demographic Research, 48(4): 89-106.

DOI: 10.4054/DemRes.2023.48.4

How to cite the data of the HMBD?

See the recommended citation