For the first time more babies have been born by couples who are not married or living in civil partnerships in England and Wales.
The latest figures from the Office for National Statistics (ONS), for 2021, show 624,828 live births in the two nations.
Of these, 320,713 (51.3%) were registered to women not wed or in a civil partnership.
The percentage of births registered to cohabiting parents has also increased compared with a decade earlier.
Mothers aged 30 years or over were almost twice as likely to be in a marriage or civil partnership (60.5%) compared with those in their 20s or younger (31.2%) in 2021.
The average age of mothers giving birth rose to 30.9 years in 2021, up from 30.7 the previous year, the ONS said.
The average age of fathers stayed at 33.7 years.
The ONS said 2021 is the first year the number of live births registered outside marriage or civil partnerships has exceeded those registered within them since records began in 1845.
It follows a long-term trend of declining marriage rates and increasing numbers of cohabiting couples seen in recent decades, the ONS added.
The statistics body said that as the full impact of the pandemic on marriage and civil partnership statistics is not yet known, caution should be applied when interpreting its latest figures.
Some 36.5% of all births were registered to parents living together, compared with 31.2% in 2011.
The most popular day for babies to be born was September 27 and the least popular was December 26th.
Stillbirths were most common in women aged 40 and over, with a rate of 5.9 per 1,000 births, the ONS said.
This was followed by women aged under 20, at 5.0 stillbirths per 1,000 births.
A stillbirth is a baby born after 24 or more weeks which did not breathe or show signs of life, the ONS said.
The highest stillbirth rate was among babies from the black ethnic group, at 6.9 per 1,000 births.
Stillbirths remained more common in the most deprived areas, the ONS said, adding that the rates have been higher for mothers living in these areas consistently since 2015.
The stillbirth rate in the 10% most deprived areas in England was 5.6 stillbirths per 1,000 births, compared with 2.7 per 1,000 births in the 10% least deprived areas.
The most popular date of birth in 2021 was September 23 while the least common was December 26.
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