Image: Yle

“Yesterday when it was -11 degrees Celsius, ten-month old twins Anni and Aatu slept 3.5 hours outside, but this morning they just took a one-hour nap inside,” says mom Outi Rajanen, echoing study findings.

Special precautions should, however, be taken when putting infants to sleep outdoors, notes researcher Marjo Tourula. Babies need to be bundled warmly and should not be left out for extended periods.

According to Tourola, -5C is the optimal temperature for outside slumber. The study indicated that parents seem to know how to dress their babies adequately at this temperature.

The practice of parking sleeping babies outside became widespread nearly a century ago, when it was first promoted by the father of Finland's maternal health clinic system, Arvo Ylppö.