There were 183 deaths in England and Wales in 2024 of babies who died before their first birthday and whose cause remained unexplained after investigation. The Office for National Statistics (ONS) dataset published on 1 October 2026 says the 2024 count is provisional. Of the total, 107 were coded as sudden infant deaths and 76 as deaths with an unascertained cause. The ONS groups these two classifications together as unexplained infant deaths. “Infant” here means a child aged under one year. The count covers deaths occurring in England and Wales, even when the baby’s mother usually lived elsewhere. It is not a count of every infant death with no causal explanation in ordinary language; it is limited to two categories identified in the ONS coding and post-investigation records.

This release also marks a change in publication format. On 1 October, the ONS discontinued the narrative bulletin and published the updated material as a dataset with tables; the statistics remain designated accredited official statistics. The workbook cover says the 2024 figures use records received up to 26 June 2026. The 2024 figure is therefore still provisional. In the same workbook, the 2023 count was finalised after being revised upward by 30, from an earlier provisional 164 to 194. This revision matters for comparison: the 2024 count of 183 is 11 below the current final 2023 total. It does not mean that the 2024 count is final; additional late registrations can still arrive.

The ONS rate uses live births occurring in the same calendar year as the denominator. There were 594,677 live births in 2024, so 183 unexplained infant deaths equate to 0.31 deaths per 1,000 live births. In 2023, 591,073 live births and a final count of 194 deaths produced a rate of 0.33. This is a rate per births, not the raw number of deaths and not an individual baby’s personal risk. The denominator is also not the total number of infants living in the country. Matching the definitions and years of numerator and denominator makes annual rates comparable; counts alone do not account for changes in the number of births. The ONS does not publish subgroup rates based on fewer than three deaths and marks some small cells as unreliable.

The two underlying classifications also need to be kept distinct. Sudden infant deaths are coded to ICD-10 R95; this can include wording such as sudden infant death, “cot death”, SIDS or similar terms on the death certificate. R99 is the code for other ill-defined and unspecified causes of mortality; according to the data notes, it covers records where the only stated cause was unascertained. The ONS says certification practices can blur the distinction between these categories, which is why both have been included in the combined unexplained-death analysis since 2004. In 2024, 107 cases were coded R95 and 76 R99. These statistical classifications do not provide a clinical explanation of cause or an assessment of preventability. They cannot support conclusions about family behaviour or the circumstances of an individual case.

The age breakdown shows when the deaths occurred, but does not by itself explain why. In 2024, 41 deaths occurred in the first 28 days after birth, while 142 occurred from 28 days up to the first birthday. The latter is called the post-neonatal period. Within it, 43 deaths were recorded between 28 days and two completed months, 30 between two and three months, and 20 between three and four months. These age bands partition the same total of 183; they should not be added to it as if they were extra cases. The ONS dataset links death records to birth records where possible to analyse characteristics including birthweight and parental information, but small numbers can make subgroup rates unreliable. Occupational classifications are also coded for a 10% sample of birth records.

Late registration is especially important because most unexplained infant deaths are referred to a coroner and the death registration can take longer than usual. The ONS extracts its data around 18 months after the reference year ends, aiming to capture most deaths for that year. A small number of registrations may still arrive after the cut-off. The figures are organised by the year the death occurred, so they are not directly interchangeable with general death tables organised by the year a death was registered. The ONS also excludes deaths of babies usually resident in England and Wales that occurred elsewhere. The count of 183 should therefore be read together with its defined coverage and extract date, and the 2023 revision should not be confused with that year’s earlier provisional estimate.