The most popular time of the year for conceiving children has changed from the spring in Victorian times to December, according to research.
A study of around 130 million historic birth records reveals that Victorians typically became pregnant in the spring months.
A surge of almost 20,000 more babies were born in January throughout the 1800s than in any other month, a report by family history website ancestry.co.uk said.
By contrast, December conceptions are more common today, suggesting that the change could be attributed to central heating.
"The cold winter months acted as a natural turn-off for our ancestors, with Victorian women typically wearing multiple layers to bed and sometimes even being sewn into their underclothes for extra warmth," the report said.
"Underwear aside, this trend can also be attributed to the fact that many Victorian weddings took place at Easter because it was one of the few times a year that industrial workers were given a holiday.
"In a society governed by strict social conventions, this was also the first time that many young couples were able to legally consummate their relationship, explaining the increase in January arrivals."