More babies were born outside marriage or a civil partnership in England and Wales in 2021 than within.
It is the first time that has happened since records began in 1845, the Office for National Statistics (ONS) said.
There were 624,828 live births in 2021, it reported, of which 320,713 (51.3%) were registered to women who were not in a formally recognised relationship.
The figures reflect a long-term trend during which the number of marriages has declined while more couples have decided to cohabit instead.
Age makes a big difference, however. In 2021, new mothers aged 30 and over were almost twice as likely to be married or in a civil partnership (60.5%) than those under 30 (31.2%).
The average age of mothers increased to 30.9 in 2021, while the average age of fathers remained at 33.7.
The most popular date of birth was 23 September, while the least common was 26 December.
Coronavirus may have affected the statistics, the ONS said, causing “delays in birth registrations”.
Birth registration services in England and Wales were “temporarily suspended in March 2020”, it noted.
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Births should normally be registered within 42 days, but in 2020, 42% of registrations came in after that time, while in 2021, 26% arrived after 42 days, the ONS said.
For that reason, it included “all births up to 15 May 2022 in the 2021 dataset”, to ensure the stats were as “complete as possible and comparable with previous years”.
Stillbirths were most common in women aged 40 and over, with a rate of 5.9 per 1,000 births, the ONS said.
That was followed by women aged under 20, at 5.0 stillbirths per 1,000 births.
The highest stillbirth rate was among babies from the black ethnic group, at 6.9 per 1,000 births.
If a baby is born after 24 or more weeks and does not breathe or show signs of life it is an event defined as a stillbirth, the ONS said.
