Percent of trials with enrollment year preceding registration year (1999-2025)

Published: November 2025, data up to June 2025

The analysis includes data on all retrospective trial registrations reported in the WHO International Clinical Trials Registry Platform (ICTRP) for the period 1999 to mid-2025. Retrospective registration is a registration of a trial after enrollment of the first participant. In general WHO discourages retrospective registration for a number of reasons, although retrospective in a short timeframe (no more than a few weeks from first enrollment) is preferable to no registration at all. See more on scope of ICTRP below.

See also: 

What you see | Scope and limitations | Data sources | Previous versions

What you see

Chart A shows the trial registration for the period 1999 to June 2025 by year, colour-coded by WHO region. Chart B shows the percent of trials with the enrollment year preceding the registration year by WHO region.

Points to note:

• Globally, there has been a steady increase in the number of trial registrations in ICTRP during the 1999–2025 period, with a brief decrease in 2022 and 2023. Trials are predominantly registered in three WHO regions: Western Pacific, Europe and now South-East Asia ahead of Americas. The WHO region in which the fewest trials are registered in ICTRP, is Africa (select Africa in the Region key, chart A, or hover over bar).
• The proportion of trials prospectively registered has improved over the period 2000 - 2024.
• South-East Asia region has the most efficient registration of trials since 2019.
• However in 2024 and 2025 we see an increase in retrospective trial registration, particularly in Eastern Mediterranean and Europe where up to 40% of trials are retrospectively registered. 

To explore the data further

• Hover the cursor on a data element of interest to see more information in a popup window (e.g. a regional segment from the year specific bars in chart A, or a point in a trend line for the number of trials with retrospective registration in a given year in chart B).
  -- For example, hovering on the segment of the bar for the Unknown region in 2022 (chart B) shows that 4,104 trials were registered in that year.
• To filter results by region, click a region from the key (chart A). Chart A will illustrate the number of trial registrations by year and chart B will display the trend line for the percent of trials with enrollment year preceding the registration year for that region.
• Hold the Ctrl key to select more than one region.
• Undo a selection by clicking ‘undo’ or ‘reset’ near the bottom of the page or by clicking the same element again.

Limitations of the data and analysis

• There are several gaps in the ICTRP data source which required data cleaning to uniformly classify data elements when possible. In some cases no information was available, e.g. unknown region and country grouping.
• The data presented in the ICTRP visualizations utilizes classifications that are not mutually exclusive. For example, a registered trial can recruit participants from multiple study sites, located in multiple countries and regions. The number of trials reported across the different visualizations is therefore not equivalent due to some duplication.
• The data is drawn from ICTRP data at the end of June 2025. This enables accurate reporting of data from 2024 to allow for some lag in data entry. This also means that 2025 data is inherently incomplete and is not indicative of the state of 2025.
• The analysis will be updated at regular time points but time lags with the scheduled updates by the data sources are inevitable. Accuracy and completeness of the information is the responsibility of the data source, see  terms and conditions of use.

Data sources

• WHO International Clinical Trials Registry Platform (ICTRP)

Previous versions

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